CRUSTACEAN PLANE'rON Or' THE ENGLISH LAKE DISTRICT.
4 i 1.
The Crustacean Plankton of the English Lake District.
B~ ROBERT
GURNEP,
n w , F.L.S.
(PLArrx 23 and 3 Text-figures.)
[Read 3rd Mag, 1923.1
THEpublished information with re$ard to the Crustncea of the Lake District
is surprisingly scanty. Mr. Scourfield has included all available records in
his Synopsis of British Entoinostraca (1903-4), but naturally dealt only with
the district as a whole, without comparison of the fauna of the different
lakes. Miss Pratt's paper on the Entornostraca of Lake Bassentliwaite is
the only attempt that has been made to give a comprehensive account of the
Crustacea of any single lake. The phytoplanlrton, on the other hand, is
fairly well-known as a rcsult of the work of Messrs. West and of Dr. Pearsall.
The fo!lowing account of the Crustacea of the district lays no claim to
h i n g exhaustive or even to deal with many of the points of special interest,
but a t least it may serve as a groundwork for comparison with other lake
areas and to draw attention to queslions 011 which further work is required.
The material a t my disposal consists chiefly of a series of plankton samples
taken by Dr. W. H. Penrsall during 1921 and 1922 for the purpose of a
study of the phytoplankton, and I wish to erprcss my thanks to hiin for the
loan of these collections and for thg valuable information which he has
rcadily given to me during the course of the work. I have also myself
visited the district and have made collections in a few of the lakes. During
the aiitumn of 1928 I spent a week in the western part of the district
specially investigating the Crustacen of Ennerdale, Wastw:iter, and Coniston.
While it is probable that tlie collections a t my disposal give a. fairly complete picture of the composition of the crustacean plankton of the various
lakes, it is unfortunately true that the methods which are suitable for the
collection and preservation of phytoplankton arc by 110 nieans so for the
Crustacen ; and for this reason, though Dr. Pearsall's collections extend over
a large part of two years, it is not possible to deduce from them any reliable
conclusions a s to the seasonal distribution and variation of the Entomostraca.
Undoubtedly much further work remains to be done with regard to these
t w o questions, and also in connectiou with the vertical distribution of the
species. It seems also to be probable that the distribution of' the Crustacea
may not be uniforni in some of the larger lakes, and that suoh lakes should
not, therefore, be dealt with as homogtineous units. For instance, the composition of the plankton in the deep Part of Ennerdale is not the same as
:m*
412
MR. It. GIJRNEY ON T H E CRUSTACEAN PLANKTON
that of the shallow western part, and the same may be the case witlh Ullswater, Windermere, and, perhaps, Coniston. 1IlolopetlizLni gibberzinz was not
found in any of Dr. Pearsall’s collections from Windermere, hut it, was taken
there many years ago by Beck, and again in 1912 by Mr. P. A. Buxton.
It may be that it is a permanent inhabitant of the lake, but it is restricted t o
certain parts of it..
FIG.
1.
XRP
of the English Lake District, with mction showing the relation of
scenery and gradients to the underlying rocks.
(By permission of Dr. R’. H. Pearsall ;md the Council of the Royal Society.)
I have thouglit it well to add notes on some of the species composing the
pl;inkton, and on the fauna of some of the high-lying lalielets or tarns, in
order t o give a more complete picture of the crustacean fauna than v;onld he
conveyed by a statement OE the composition of the plankton alone.
IVith the physical conditions of the district and its lalies it is not 11ly
business to deal, Tlie foundation of our linowledge of these lakes was laid
in the survey of Ur. H. H. Mill (1895), and Ur. Pearsall hau, in his papers
on the aquatic flora and pliytoplanliton, added greatly to our Irnowletlge of
the post-Glacial history and present conditions of these lakes. The accompanying i m p clearly shows relations of the lakes, w liich occupy vallej s
radiating from a coxnnion centre.
THE PLANKrON.-(
‘ o m p i i s o n o j the r w i o u s Lakes.
One of the chief results of Dr. Pearsall’s work is that “the stage of
evolution of the lake-basin must be regarded as beiiig tlie fclndaniental factor
itffecting the distribution of the pliytoplanliton, since it is u p o ~this fiictor
that the character of the waters depends” (1921, p. 279), and he has divided
the lakes into groups on the basis of the ariiount of silting of their beds.
These groups are :I. Primitive Lakes.
Wastwater, Ennerdale, Buttermere, and I h m m o c k .
TI. Intermediate Lakes.
Hawes Water, Derwentwater, Basscnthwaite.
TIT. Evolved Lakes.
Coniston, Windermere, Ullswater.
IV. Most evolved Lakes.
Esthwaite (and Grasniere).
The phytoplankton corresponds fairly well with this grouping, the lakes
of the first group containing a Desriiid plankton, while in the remainder
there is a large proportion of Diatoms. But Desniids are also frequent in
Group IT., while Myxophycez form an increasing coniFionent of the plankton
of Groups 111. and IV., and are at tiuies dominant in Esthwaite. As
L)r. Pearsall intends to deal in detail with the plankton as a whole in relation
to its environment, I shall do n o more than attempt to show how far the
distribution of Eutomostraca conforills to this grouping.
Any grouping of these lakes on the basis of their Crustacea is by no means
easy, since, with the exccption of Buttermere and Crummock, which lie in
the same valley and undoubtedly a t one time fornied a single lake, each lake
has its own individual character-so much so that it would probably always
be possible to identify the lake froin which any given representative sample
of plankton was taken.
I n Table 1, T have arranged the lakes in the groups adopted by Dr.
Pearsall, Group I. being the most primitive and least silted, and froin this
table the compositioii of the Crustaceaa plankton can be seen a t a glance.
Every plankton species taken is recorded in the table, b u t those which
occurred on1.y singly in one collection or were evidently not regular constituents of the plankton :ire di,~tinguiahedhy x cross enclosed in a circle.
411
MR. R. GURNEY ON THE CRUSTACEAN PLANKTON
-
F;
42
k
*
c:
5
i
0)
f
E
!i
2F1
c3
*
9
__
3-
1
3
5
__
I
Sida crystallinn . . . . . . . . . .
Uiaphanosoma brachyuruin @
Holopediunh gibberurn . . . . . .
Duphnia hyalinn 8. str. . . . .
,, lacustris . . . . . . . .
,, galeuta . . . . . . . . .
Cerioduphiriu ! p ulc'~ella
qundraiigula '
Bosinina lonyirostris. . . . . . . .
i
Polyp'hen~uspediculus . . . . @
Bythotrephes longimanus . .
Leptodora kindti
+
Limnocalanus inaci*tirus . . . .
Diaptom.us laticcpa . . . . . . . .
gracilis ......
c'yclops leuckarti . . . . . . . . . .
ubysso?wn ........
........
i1
1
.
+
.
Number of species
+
...
.I
+
5
..
9
..
+
+j
11
+I
+
. . ..
I+
. .I . .
.. . . . . . . . . +
.. . . . . .. .'
.. . . . . .. . . . .
.. + +
.. +
..
..
..
..
12
-
..
+
..
9
-
+
3
+
+
+
..
+
t
..
+
+ + +
+
+
+ +;+ + + + +
.. . . . . + + * . +
+
..
..
+
..
+ +
+ + + +
+
.. .. ' +
+ + +
..
;I:
- ~-- - 9
3
5
7
+
+
-
-
9
8
I
It should be noted further that collections have only been taken from the
shore of Buttermere, and that I have only a single collection from Grasmere,
taken i n September 1912. Species which are known to belong t o the littoral
fauna, such as Alonopsis elonyata, are omitted even when they have sometitnes been taken i n the plankton. Chydoms splirtricus, which is often
limnetic in central European lakes, is not found in the plankton of this
district.
It will be seen a t once that the Crustacea do not conforni to Dr. Pearsall's
grouping, and indeed it is diffianlt to trace definite relationFhips a t all.
O F T H E EN(;I,ISH
I A K E UISTHICT.
415
Group I. of the lakes of the deep and rocky type agree in the limited number
of species and the absence of species characteristic of shallow and warn:
waters, and in their predominant zooplankton, whiln Ennerdale and Wastwater
together differ from Butterinere and Cruiniiiock in the entire absence of
Daphnia. Butterinere and ~ ~ r u n i n ~ oare
c k characterized by the doniinancc
in their plankton of the typical form of Daplinia 1iyaZina. But, althougll
Ennerdale and Wastwater are so alike in physical characters, they differ
markedly in their plankton, not only in the species found, but in their
relative abundauce. Ennerdale possesses two striking species, H o l o p e t l i t t ~ ~
yibberunz and Limnocalaiius mucrurus, which are al)sent from Wastwater,
but, on the other lixnd, lacks both LeptocEora lii)ulti and Cyclops abyssorurn,
110th of which are comnion in Wastwater. Further, Bosnaina obttrsirostris il;
xbunrlant in Wastwater, while it is an insignificant coniponent of the plankton
of Ennerdale. It cannot, in fact, be said that the Crustacea indicate ally
greater relationship between these two lakes than between either of them
and certain lakes in other gronps such as Hawcs Water, Ullswater, 01’
Uoniston. I n these two lakes Dr. Pearaall’s grouping is put sharply to the
test, for, so far as physical conditions go, two lakes could hardly be 1nore
alike than these, and their phytoplankton also is very similar.
The mine difficulty is met with in the other groups, though it is true that
Esthwaite has Characters whicli distinguish it very clearly. It has :L very
varied plankton, which contains the “ warm-water ” or lowland Crustacea
JXaphunosonzu brachyuru?n, Cerioduplinia, and Cyclops leucharti; but its chief
claim to dislinction is the presence (in company with B. obtzisirostris) of
l’osnbina Zotigirostris, whicli is a distinctly southern form. (hasmere, except
for containing IIolopetZiunz,is very similar to Esthwaite.
I n Qronp 11.it is clear that Hawes Water cannot be classed with Derwentwater and Bassenthwaite with regard to their Clrustacea. The prcsence of
the northern species Iliaptonws laticeps places it in a class apart, its elevation
of 694 feet giving it almost a position amoiig the mountain tarns. It differs
also from the other two, possibly for t,he same reason, in the different race of
11uphnia inhabiting it, and also in the absence of Sida, Leptodoya, ant1
Cyclops leuckarti.
Dcrwentwater and Bassenthwaite also differ considerably, though forming
part of one drainage system, for the latter lacks any species of Dapl~niaor of
Bosmina, being unique among the lakes in this respect. It is true that both
have been recorded from it, and that a single specimen of Bosmiiia obtusirostris occurred in one sample examined hy me ; but it is evident that, a t the
present time, neither can properly be included in its fauna. The great
abundance of Diuphanosoma in the plankton of both lakes is a striking
feature in common, and the plankton of Bassenthwaite may perhaps be
regarded as that of Derwentwater, in which certain elements have been
suppressed.
416
AIR. It. GURNEY ON THE CRT’STACEAN PLAKKTON
Dr. Pearsall suggests that the impoverishment of the planlston of Bmsenthwaite inay be due to tlie silt from lead mines waslied into the lake during
the past fifteen or twcnty years. I t is quite possible tliat to this-cause is due
the difference between the present plankton ntid the list given by Miss Pratt
in 1898.
Group 111. is also by no means a natural group froin the point of view of
the Crustacea, although the fact that it is only in the three lakes-Coniston,
Windermere, and Ullswater-that 1,aphrtia of the yalrata-form occurs, may
i n d i c a t ~a siniilarity of conditions. The pesence of ffolopedium, either
regularly or occasionally, ill Ullswater and Windermere may also be regarded
as evidence of similarity, though the status of the specie3 in the tlist,rict is
rather doubtful. It seeins to me that, if any grouping is to be attenipted on
the hasis of the crustacean planliton, Ullswater aud Hawes Water should be
included in the series of primitive lakes, while Winclerniere, with its Diaplianosoiiia, Ceriodupluhnia, and Cyclops leuckarti, belongs inore nearly to the
Esth waite-Grasmere series. Coniston, with its dominant crustacean plankton,
conies near t’he primitive type, while Derwentwater arid Bassenthwaite lead
on towards the more evolved type of Windermere and Xsthwaite.
It is impossible, without greatly extended kiiowledge oE the food requirements of the ~ntomostraca,to determine what are the factors controlling
their d i s t r i h i o n s in an area such as this. The evideiice is conflicting.
Birge (1898, p. 353) states that hapltnia feed readily on filamentous Diatoms
(e. g. Alelosira) and also on Apliankomenoic and AiiaEmLa, while Biaptomus
prefers B~zubcwuand Apltu~iizoinenonto Diatoms. On the other hand, more
recent investigations lead to Ihe supposition that but little correspondence
will be found between the distribution of the Entotnostraca and the net
phytoplankton, since the Entomostraca appear mainly to feed upon the
minute nannoplankton, which is not taken in the plankton net. Woltereck
(1908) stated that the net plankton is far too large to be taken in by Daphnia,
their food consisting partly of the finest detritus, but mainly of the nannoplankton. The latter he found to be more abundant in the Lunzer Obersee,
where Bapltniu was more flourishing, than in the Untersee, and attributed
this to tlie greater organic contont of the water. This result was confirmed
by experiment, since it was found 1)ossible to niaintaiii limiietic Daphnias in
health 011 a diet of a pure culture of Chlorella.
Naumann * concluded that it was not the A l g ~
theniselves but the detritus
produced from them, and tlie snialler Flagellates, which proyided the food
for the Crustacea, and that the dust-fine organic detritus or peritripton, which
may be introduced into the iake from without, may be of the utmost
importance in the lime-free P a l ~ o z o i cregions. I n such lakes the zooplankton is greatly in excess of the phytoplankton. The lakes of the
*
I have not been able to consult Piaumanii’s paper, but re11 011 a review of it in Arch.
f. Hydrob. xii. 1920, p. 835.
‘$17
OF THE ENGLISH L 4 K E DISTRICT.
lowlands of north and middle Europe are, on the other hand, rich in electrolytes, the phytoplankton is abundant, and the zooplankton feeds on the
detritus derived from it.
Considerations such as these offer a possible clue to the understanding of
the composition of the zooplankton, hut leave untouched the problem of the
distribution of the predaceous Chlocera such as Leptodoru.
The factor which appears chiefly t o influence the distribution of the
Crustacea in this district is depth of water. A fair idea of the relative
depth of the lakes is given by the following table, showing the percelltages
of the area covered by depths of 50 or 100 feet.
.
TABLE?.-Depths
of the Lakes.
Figures from H. R. M111, 189.5.
I
Percentage of area covered by
23
:a
...
219
43
63.6
Ullswater
......
205
35.2
64
Coniston
......
......
184
37.1
60.8
148
54.6
67%
Urummock. . . . . .
144
27
47
..
103
64
98.3
Buttermere . . . .
94
87.8
100
..
..
72
93.9
100
70
94.1
100
Windermere.
Ennerdale
Hawes Water
Derwentwater
Bassenthwaite
~~
I n bome cases this does not give a true impression, since, in the case of
Ennerdale, Windermere, and Ullswater, there are deep and shallow Imins.
Mill divides the lakes into a deep and a shallow class, the latter including
only Derwentwater and Basssnthwaite.
N o w , the species of plankton Crustacea may be roughly arranged as Coldwater, Eurytherm, and Warm-water species, and it is found that the
proportions in which these classes occur in the lakes vary in fxirly close
accordance with the depth. It should be noted that, in the following table,
the lakes are arranged according to the percentage of depth over 100 feet,
but Ennerdale is placed next to Wastwater, in view of the configuration of
its eastern trough. Windermere and Hawes Water are more or less intermediate between the deep and shallow lakes in the character of the plaiihton,
418
MR. H . Gl!RNEY ON THE CllUSTACLAN PLANHTOK
but the foriner should be specially studied with a view to seeing if, as 'is
probably the case, the plankton of the deep and the shallow basin differs in
composition.
TABLE3.-coin position of the Plankton.
1
Wastwates
,
Cold-water Species.
I
Eorythsrm Species.
3
I
3
.,
2
3
-
......
Windermere . . . .
Ullswater . . . . . .
Hswes Water . .
Derwentwnter . .
Bmsenthwaite . .
Coniston
ERthwdte
)
2
3
3
1
-
......
1
~~
Tlw A'orthern &lenient in the Plankton.
The general character of the plankton is very distinct from the Central
European and Baltic types and resembles that of Scotland. Characteristic
of it is the absence of' Daphnias of the cuculhta-group and of Bosmina
longirostris from all the lakes except Esthwaite and Grasmere, and of
C'eriodaphnia from all but Windermere and Eethwaite.
The general abundance of Bosmina obtzrsirostris in itself marks the
plankton as of the northern type, but the following species are also
characteristic of northern or arctic lakes :Holopediuin yibberum.
Daphnia hyalina s. str.
Byt1Lotrephe.s longimarius
Polyphenlus pediculus.
niaptomus laticeps.
Limnocalanus macrurus.
Cyclops abyssorurn.
Biaphanosoma brachyurunt may be looked upon as belonging to a southern,
warm-water, genus, but it is itself so widely distributed throughout Europe,
in cold as well as in warm waters, that little importance can be attached t o
O F T H E lCN(;LISH L A K E UIS'L'HlCT.
'il!]
it in this connection. I t is found only in the summer months and lias an
extremely short life-cycle, a fact which has probably largely assisted it to
accommodate itself to a great variety of waters.
Leptodova kiiidti, although in deep lakes it may have a preference for the
lower or colder strata, is by no means restricted to deep lakes, nor is it
characteristic of northern regions. It may rather be regarded as a southern
element in the fauna.
Although the crustacean plankton of the Lake District has a distinct
northern facies, the absence from it of Diaptomus lwciniatus and 1).wievzejslii,
which are not uncommon in Scotland, is noticeable. The latter is a eurytherni
species of remarkably wide range, but characteristic of pools rather than of
lakes, but the former is a de6nitely arctic-alpine species. Biaptornus laticep
is a member of the group of northern Diaptomus which is widely distributed
in Scotland, but only occurs in this district in Hawes Water and Goats
Water. T t seems probable that it may be a recent immigrant.
Froin the point of view of the (Irustacea the Lake District plankton
certainly belongs to the Scottish Highland type, with the addition of it few
southern forms.
I t inrist be admitted that any discussion as to whether the plankton of any
lake or district has a northern or southern facies is of doubtful value in the
present state of our knowledge of the means of distribution and required
conditions of existence of the different species. Not only is the whole
question of the relation of the present fauna to the effects of the Glacial
period far from being clear, but we have little means of knowing to what
extent the fauna was able to survive that period in its original habitat. I n
the case of the Lake District it seems fairly certain that the present lakebasins were filled with ice, and it is probable that the whole district was
covered with a mantle of ice, so that the present aquatic fauna is entirely of
post-Glacial origin. It has been re-colonised largely by northern species,
because these species find here, under a lowland climate, the conditions
necessary for their existence, which are depth of water, form of lake-basin,
and chemical coinposition of the rocks of the drainage area. The similarity
of the plankton of the Scottish and Cumberland lakes, and of both with
that of some Scandinavian and Irish lakes, may be due in large part to their
being excavated in ancient lime-free rocks rather than to climatic influences.
The similarity between the arctic and alpine fauna of Entomostrana may he
accounted for by unlimited powers of dispersal rather than by the influence
of the Glacial period. It is true that the evidence from other groups is in
favour of the current views as to tho relaiion of the alpine to the arctic
fauna, but we require to know far more about means of dispersal before the
matter can be regarded as decided. I will give two instances within my
own knowledge which illustrate the danger of relying on limited powers of
dispersal and upon the nature of the habitat in speculations regarding
420
MR. R . GLTRNEY ON THE Cl(t1STACEAN PLANKTON
post-Glacial distribution. I n 1907 Aptis can,-rijorn~is,
which had not been seen
in Britain for' over 40 years, was found in Scotland by Mr. Balfour-Browne,
but had again disappeared the following year. Liinnicytliere nairabilis is
claimed by Zscholike as a member of the deepwater fauna of the Swiss lakes,
which is of northern origin and finds only in deep ~ a t e r sthe conditions
necessary for existence in its southern station. But in 1905 I found this
species in a shallow rnin-pool near Biskra in Algeria, and another species,
L. iwisu, in a stream which irrigates the Oasis of Oumach.
The Plankton
oj'
3imerdale T17ateil*.
The discovery of Limnocalanus macr*urusin Ennerdale indicated a t least a
possibility that other '' relict Crustacea might be found there, and made it
most desirable that the lake should be carefully explored. With this
purpose in view I visited the lalie a t the end of September 1932, and made
special efforts to collect the Crustacea of the deep water. The lake is shallow
at, its western end, but the eastern part is a deep narrow trough with a
maximum depth of 148 feet. T h e shores a r e rocky, and with a very steep
slope.
The weather during my stay was unfavourable, but I was able to search a
large part of the deep trough with a coarse tow-net and light dredge, and
also to take plankton samples on three successive niglits. Neither Mysis
relicta nor any Amphipods were taken. This negative result should be tested
by examination of the stomachs of Char (Sulnao alpinus), but I have not
been able to obtain specimens.
Table 4 gives the compositioii of t.he plankton between September 27th
and 29th. It is of course impossible to obtain accurate information as to
the vertical distribution of plankton without the use of a closing net and a
succession of short vertical hauls, but I do not think that such accuracy is, in
general, necessary, and a fair approximation t,o the truth may be got with
less effort and simpler means. My own collections were made with an
ordinary m a l l plankton net, which was let down, together with a weight, to
the required depth and then towed a distance of about 100 yards. Naturally
the net fished both going down and coming up, but the results of the different
hauls are so distinct that t'hey do in my opinion give information as to the
vertical distribution. I have not attempted to compare different hauls by
absolute numbers, but have counted the individuals of each species in the
whole or in part of the collection, and expressed their frequency as percentages
of the whole number of individuals of all species count,ed. This method gives
an accurate statement of the comparative frequency, though not of the absolute
numbers of any species, and it admits of a cornparison being tnade between
samples from the same or different lakes however'they may have been taken.
Siinilar figures are given for Wastwat,er. and Coniston for purposes of
comparison.
''
nv THE
421
ENGLISH LAICE DISTRICT.
TABLE.I-.-Composition of the Plankton of Ennerdale, Wastwater, and
Coniston.
The figures give numbers of individuals of each species per cent. of whole number counted.
-
I
-~~
-
-
~
.
...
Bythotrepltes l u i y i m r c w r s
Bosmina obfusii.ostri8
Diuptonius grncilis
.....
Limi~ocalunusmucrui'us
-
1
I
.
CONISTON.
Oct. 2, 1927.
Snrr*nre.
Surface.
Fine Net. Coarse Net. 60-80 feet.
I
1
Below
100 feet.
422
MR. R. G U R N E Y OX THE CRUSTACEAX P L A N K T O N
Jt is clear from the table that the plankton is by no means uniform
throughout the lake either vertically or horizontally, neither is it the same
by night and by day.
The chief component of the plankton is Iliaptomus gracilis, which is
distributed throughout the lake, but is relatively more abundant in the
western end than in the deep eastern trough, and has a distinct preference
for the surface. The figures given €or the deep-water snniples must be
discounted to some extent, owing to the fishing of the net going down and
coming up. It is curious that this species seemed to be present in absolutely
smaller numbers on the surface by night than by day.
Limnoralanus is also distributed all over the lake, but is found only in
small numbers in the shallow water. It abounds both on the surface and in
deep water in the eastern trough, and may greatlJ- exceed 1).graciiis in
numbers. Although common a t all times on the surface, it is noticenldy
more abundant during darkness.
Holopedium gibberum is only exceptionally found on the surface by day,
but is common in deep water, and at night forms a large part of the surlace
plankton.
Bosntina obtwirost&, though apparently fairly common at some seasonp,
was almost ahsent froin the lake a t the time of my visit, the few specimens
taken being iri deepwater samples.
A curious feature of the plankton was t l i u appearance of Sida crystallina
on the surface a t night. I t was not taken during tlie day in any collections
in open water, but occurred in three out of four plankton samples taken a t
night. All these samples were taken a t the surface over water 80-120 feet
deep, the only sample in which Sida was not found having been taken in
shallow water. The specimens taken were almost all males.
THE
ENTOMOSTKACA
OF THE TARNS.
The occurrence of Ihaptonzus Zuticqu in Hawes Water and in Goats
Water (as recorded by Bradp) raised the expectation that the fauna of the
high tarns of the district might prove t o include other species representative
of the arctic-alpine Entomostraca which do not occur in the lakes, and, a t
the elid of September 1922, 1 visited some of these tarns and made
collections in them and in pools and bogs up to a n elevation of about 2000
feet. The resnit did not fulfil expectation, since D.Zaticeps was not fonnd in
any tarn other than Goats Water. There was also a notable absence of the
northern forins of Harpaticid, with the exception of Canthocamptus cuspi&?is, which seeins to he comparatively coninion in Sjdiaynvm in running
water where the temperature is low. Nevertheless Z think the results are of
sufficient interest to be given in some detail. The completr list of species is
sl10wn in tabular forill.
OF THE ENGLISH L A K E DISTRICT.
42 3
1. Floutern Turu. This tarn, which is fairly deep and contains trout, lies,
a t :I height of about 1250 feet, just on the east of the watershed between
Ennerdale and Crummoclr valleys, in a deep hollow in the grassy moor. It
is on the edge of the area of the Skiddaw Slates, the granite hill of Great
Borne rising steeply on the south. All around the tnrn is swampy grouud,
with trickling springs and hollows filled with .t$diagnmi.
The water is dark and peaty, and the marginal vegetation consists of
Littorella (dominant) and LobeZia. The tarn drains into c:rummocli.
Seren species only of Entomostraca were taken, Bosminci ohlwiiroslris being
the dominant species. A large proportion of the females were ephippial,
but only one male was seen. Very few females carried summer eggs, PO that
the colony was probably at its maximum and about to die out. Diuptoi)ius
gracilis was abundant, a large proportion being males. All were of a striking
hlue colour, but of quite typical structure.
2. Greeltdale Tarn l i v , at a height of 1320 feet, on the Borrowdale
volcaiiic series a t the head of a glen north of Wastwater. West of it is a
gently sloping moor, while east of it rises the bare rocky Middle Fell. The
tarn is very shallow, with clear wzter and stony bottom, the vegetation
consisting of Lolwlia, Littorella, Pallitriche, My&pliyllum, and fsoetes.
While I was unfortunately unable to take the temperature, I can say that
the water was (Oct. l s t , 1922) so intensely cold that it mas impossible to
wade out and collect in the open. Eleven species of Eritomostraca were
taken, among wliich I)icyAai7osoina braclyurion was the most abundant.
Bosrnina was common, hiit none were ephippial. 1)iuptomus gracilis was
abundant, and here of a fine red colour *, but the majority were imimture.
AZonopsi.s elongata was abundant, but none were sexual.
3. Lerers Water, altitude 1350 feet, lies on the Borrowdale volcanic series,
and is a rather large, nearly circular, tarn in a barren rocky corrie. I t owes
its existence to a morainic dam, but its outlet is artificially controlled and its
level somewhat raised for the supply of water to the Coniston copper works.
The floor and sides of the tarn are rocky and without any vegetation, and
Entoinostraca are almost absent. The only species found in quantity was
Alonopsis elongata, and, liesides this species, only a single individual each of
&s&a
obtusirostris and A i ~ o p w c sliarpic were taken in spite of prolonged
search. On the other band, B. obi7isirostris was found common in quite a
sm:ill pool near the tarn.
Tho lifelessness of this tarn is rather remarkable, a n d I can offcr no
explanation.
4. Low Water, at a height of 1786 feet, lies in a circular corrie beneath
the crags of Coniston Old Man, and is, as Levers Water, imrtly dammed for
+
\Vard (1904) notes specinllj the red coloiir of copepodv in elevated Inkeu,
424
M R . R . GURNEY ON THE CRIJSTACI“AN PLANKTON
the service of the mine?. It also is rocky, deep, and without vegetation, the
water rather dark coloured. The fauna consisted of four species only, and
these in small numbers. Diaptonzus gracilis was here of :I rich red-orange
colour. A curious feature of the fauna was the extreme blackness of the
Alonopsis elongata, which proved to be due to the retention of the old shell
a t moulting. The majority of the individuals showed three old shell valves
adhering and forming “lines of growth.” I n other tarns and in the lakes
similar individuals WPTB occasionally seen, but the feature was pronounced
only in Low Water. Lilljeborg mentions the same thing as characteristic of
specimens of this species from the high north of Sweden, and it is apparently
a character connected in some way with the low temperature of the habikat.
5. Gouts Water, 1646 feet, is a small tarn in a combe on the north-east
side of Coniston Old Man. It owes its existence to a dam of rocks fallen
from Dow Crags, and the water from it soaks through the dam and issues as
a stream some distance below. The water is deep and clear, the shore rocky
and entirely barren. The fauna was found to be very scanty, but six species
were taken, the most noticeable being Diaptomus laticeps, conspicuous from
its red colour.
6 . Highlow Tarn, about 2 miles N.E. of Coniston, at a height of about
600 feet, is mainly of artificial origin, being due to the union of several small
shallow tarns by the damming of the stream. Lying comparatively low,
with shelving banks, its vegetation is rich and includes Nymphma. Consequently its fauna is quite different from that of high tarns. Ceriodaphnia,
Polypliemus, and Bosneina longiyostris are common, and Volv0.2: was present
in such quantity as to give the water a thick grecn colour.
7. Sphagnum pools and sprinLy waters.‘
On the high ground of the Ploutern Pass and round the foot of Coniston
Old Man there is much swampy ground, often with little rills of running
water, and occasional pools largely filled with Sphagnum. The water was
uniformly very cold.
By the outflow of Greendale Tarn there are a number of sniall pools
D
crenerally margined with Sphagnlcm, but one of them, which was of some
depth, was choked with Callitriche and contained some larvz of the Newt
iuolye-cristatus. These larvm were kindly identified for me by Miss J. B.
Procter, who informs me that they were either newly hatched or only a few
days old. This very late hatching is very unusual, and no doubt due to the
coldness of the water.
The Sphugnu~n.in running water was commonly tenanted by Canthocamptus
cuspidatus, a slow-moving pinlr-coloured Harpacticid which is a characteristic
northern species. I n pools and springs the moss contained either C. cuspidatus, C. zschokkei, or C. p y p u w s , but never inore than one species in one
plncc. Several species of ( T ~ / c i o p swere taken, of which the iiiost interesting
is (~'.rerziistzi.7, which i m s coininon in pools on Floutern Pass and was also
found by Greendale Tarn. It was sotne~vliatunexpected to find C. na)zus in
pools on Floutern Pass sinco I regird this species as a warm-water form.
It is worth noticing tliat, A c u n t h o l e b e ~ i scwt3irostris w:is only found in ttyo
high-lying pools. This is :I species found in lime-free hog waters, b u t it is
cyidrntly not a cold-water northern forin. AZmm mstica and Cllyydorus y i p :ire species ot' similnr preferencc, ant1 were found rather infrequently 011 the
high ground.
TABLE5.-The
Crnstacea of the Tarns,
__~__-__--__-_
........
C'eriotlnphnicz pulchelln . . . . . . . . . . . .
Bosminu lo?igirostris . . . . . . . . . . . . . .
Diuphcinosonzu brnchyuiwu
~
,,
obtusirostris
. hkry/cercu.s lamellatus
..............
..............
.4ri*oprixs h a r p . . . . . . . . . . . . . . . . . .
,410iiopsis elongnta . . . . . . . . . . . . . . . .
Alonn rrJ9ini.s ......................
Aloiirlln m n n ....................
,l
excisu ....................
Grriptolebrris testudinarin . . . . . . . . . .
P ~ l ~ ~ p A e ?pedicdus
~riis
..............
Cyclops leclcknrti . . . . . . . . . . . . . . . . . .
,, ugilis ....................
,, uiiiclis ....................
l,
.fc?tscus ....................
Ili(rptoiii~isyi.ricilis . . . . . . . . . . . . . . . .
,,
Iutieqis . . . . . . . . . . . . . . . l . .
Cunlhocimptus zschokkei . . . . . . . . . . . .
+
+..
+
+
..
+
..
..
+
+
+
+
+
+
+. . +
+
..
+
+ +
..
..
+
*.
..
..
,
..
+
..
*.
+
+
Highlow Tar11 has all the chnrncters of a lowland pool, but the remaining
tarns described are probably fairly representative of all the high-lying waters
of the district. Those exanlined fall into two groups, of the peaty and the
rocky type, the former representcd by Floutern and Greendale Tarns and
the latter by Levers \Vatel, Low Water, and Goats Water. Floutern and
Gtrecadale Tarns have a relatively rich Entomostt~acanfauna characterized
LINN. J0URN.-ZOOLOGY,
VOL. XXSV.
31
426
IMR. R . GURNEY ON THE CRWTACEAN PLANKTON
by ~ i a p h a ~ i o s o ~ while
n a , the rocky tarns of Coniston have a very scanty
fauna, both of species and individuals. The brilliant colour, either red or
blue, of D.gracilis in these high tarns is very striking.
The means of dispersal of the species is a problem of some obscurity. All
the tarns are of comparatively recent origin, owing their existence to
morainic dams o r rock-falls, and each, as a rule, occupies the head of a
lateral valley.
Keilhack, studying high-lying waters in the Dauphin6 Alps, coiicluded
that distribution of species wiis effected Ly migratory birds, antl that wafersheds rarely, if ever, exert any influence on distribntion. While it is
impossible to offer any other sntiyfactory explanation, the agency of birds,
especially in the Lakelnnd area, seems to be of doubtful efficacy. A detailed
survey of the tarns of this coinpact and uniform district, with special
reference to the dissemination of species, would probably lead to results of
great general interest.
Notes
01%
some
qf the Species.
LIMNOCALANES
MACRURUS, Xars.
The oecurreiice of this fine Cantropagid in Ennerdnle is rather a startling
discovery, and raises 1woblt:ins of exceptional interest. It was first recognized
in a collection made I)y Dr. Pesrsall on Sept. 23, 1921, the sample containing five specimens. As a result of this discovery Dr. Pearsall arranged
for a series of collections to be made in the lake, and I also visited it myself
on Sept. 27, 1922, hut, although'1 am able 'to give some account of its
distribution in the lalie antl its seasonal c,ycle, the facts are by n o means
cornplete, and can only be n.scertained by quantitative methods with suitable
apparatus. So far as information goes at present, the species is very abundant in the lake and occurs in every part of it, a t all events in autumn, which
is the period of niaximutn development ; but it is far more abundant in the
deep eastern trough, and occurs only in small numbers in the shallow western
end. All previous observations, hy Elmian and others, agree in showing
that L. ~ Z U C ~ Z L ~ ZisL Sonly exceptionally found a t the surface, and is almost
entirely confined to water below a depth of 5 metres. Further, the iliaxiinurn
temperature of water in which it livrs is 14O (j., but even when the temperatare is lower than this it does n o t come to the surface. I n Ennerdale this is
not the case. The first co1lect)ion i n which it occurred was made on thr
suri'ace (in stormy weather it is true), the temperature of the water being
14.4O C., and my owii collections between Sept. 27 and 29 proved that it lived
at that time in considerable numbers a t the surfiice, allhough it certainly was
inore abundant in deeper water, down t o ahout SO fcet. I t is impossible to
give exact figures, since I had no closing net at my disposal, but the figures
given in Table 2 (p. 417) will serve to show the distribution at that tinie
with, I heliere, a sufficient approximation to the truth. I was unfortunately
uiiable to take teniperature olservntions.
427
OF T H E ENGLTSH LAKE DISTRICT.
Diurnal migration of t,hc specirs was strongly niarlted at tlie tinie of my
visit. On t,hree successive niglits surfiice plankton sainples were taken over
t!ie s1l:illow and ~netlinm(50-70 feet) depths, and in each case Limnocalanus
was I'onntl iu niuch greater numbers than duriug the day. The figures in
tlie t:iGle do not bring ouh this fact SO clearly as would bave been the case if
:ibsolut,e numbers could have been given, but the difference between day :tnd
night plankton was quite obvious and striking on the spot.
So f a r as concerns seasonal clist;.il~ution,the facts with regard to Limnod ( o i ~ i . sin Ennerdnle are somewhat uncertain.
Ekman has shown that in
the B:il tic lakes tliere is only one breeding-period-in
autumn. Young
:11)p!:ir first in March, and by &lay the first-hatched young are fully grown.
But there is then :L jvriod of about five months during which little or no
growth t:iBes place and t!ie genitd organs remained undevelopccl. Sexual
m:ituritjy is roached in autumn, and breeding begins in Noveniber at a
temperature of about 7' C. The adults of the previous year die of? in
spring and all h a w disappeared by May.
Ur. Pe;irsall's collections may be regarded as indir:at,ing a similar life-cycle
in Ennerdale, but are by no means conclusive. Neit.her j o u n g nor adult
were taken on Feb. 18, 1922, but two adults and ni:iny young were found in
a sample froni the shallow end of the lake on April 20, though, curiously
enough, none at all were talien in a deep-water collection on the same day.
In .June and J u l y no young, hnt a very few adults, were takeu ; but in
Ortober adults were coninion in 60 ftJet of water. It seems safe to say that
youiig are only found in spring, and that adults are abundant, and even the
coriiinonest plank ton species, in Sc1)teml)or and October.
llie interest of this species lies more, however, in its geographical distri11
bution and its origin as a nieniber of the fresh-water fauna, and it is necessary
tjo go into this question in sonic detail since its occurrence in Ennerdale
raises a particular difficult geological 1iroblem.
Elinian has dealt exhaustively with the structure and distribution of
L. ,~tucrtwris(l913), particularly with reEerence to the Baltic area, and his
resiilts m a y he summarizc~tlas follows :I. L. r n a c ~ ~ z ~ rof~ c xfresh-water lakes is not specifically separahlc from
I,. yvimaltlii, which inliabits brwlcisli water in the B d t i c and Caspian Seas
:itid along the coast,s of Alaska and Siberia.
The differences are :((I) Shape of head, the dorsal contour being more swollen in L. wacriirus.
( h ) In L. p i m d t l i i the last thoracic segment is rather triangular or
I'ointed, or may liavo a minute hook-like projection, whereas it
is rounded in L. m w m r u s .
Tlie antennrr are longer i n L. grimaldii.
(ti) The I'urcal rcinii of L. yvimaltlii are longer than in L. viac~-urus.
TVliile the t.wo extreines are readily distinguished, they are united by
local v:irietiea presenting every iriternlecliatc condition.
( ( a j
31 *
428
MR. It. G U R N E Y ON T H E CRVSTACEAN PLANRTOS
2. In Europe L. m w r t w u . ~is only fourid in lakes which can he proved to
have been separated froin the sea in post-Glacial times. I t is therefore a
'' relict " form in the strictest sense. It ha3 not arrived in any of the lakcs
it now inhabits by active migration.
3. The shape of the head in L. iiiacmrtis, while not a t all variable among
iudividnals iii any given lake, varies greatly according to the locality, and
it can be shown that those lakes (in Europe) which cont:tin the extreme
fresh-water form have been separated longest from the sea, whilst in more
rece~ntlalies the Linaizocalunus approaches more nearly to the gritnuldi
form.
4. I t is evident that L. glriincr2cZii is the parent form, and that L. ?nacvurus
is a variant from it which has arisen indcpendently in ninny places, the effect
of the change of mediuni being always in the same direction. 1
5 . The first step in the traiisforination occurred in the Baltic during the
'i Ancylus Lake" period, and the Baltic lakes in which Li~nnocalanusoccurs
are relicts of the Ancyliis lake.
With the most interesting speculations of Ekrnan on the snbject of the
origin of species founded on thesc facts w 0 have no concern here.
Now, while it seems to nie that Eknian's conclusions with regard to the
Li~nnoc~alanus
of the Baltic area and of the Caspian Sea are entirely well
founded, there are certain criticisms to be made, and it is difficult to extend
his explanation to the Liiimoculaiazts of Ennerdale and the lakes of North
America in which it occurs.
I n the first place I cannot nnreservcdly accept Ekman's basis of measurement, of the head forin on which much of his argnment depends. Ekinan
has adopted the following syst,eni of measurement :(1) Head-length-to the dorsal groove immediately in front of the inandibular muscle. (See test-fig. 2.)
(2) Hend-height-B-expressed
as a percentage of half the head-length.
(3) Height of vertex above or below the dorsal line of t,he thorax expressed
as a percentage of half the heacl-length.
The last ineasuretnent is negative in all the griinaldii forms, ant1 positive
only in the extreme vzacrurus forins where the dorsal contour of the head
swells up above the dorsal line of the thorax.
Wliile the first and second iiiea~iireineiit~
are fairly definite and extraordinarily constxnt, the third seems to me so uncertain as to be of little value,
since (as Ekman Itns hiinself pointed out) tlie selection of a dorsal horizontal
base-line is a matter of guess-work. I have been quite unable to fiud agreement between his own figures for this character and the drawings of the
specimens from wliicli the measurements were taken ; in fact, these measurements cmnot, as I believe, give a real definition of the shape of the head,
which can only be shown in a drawing. Still, f o r purposes of Comparison,
I give, in Table 6, measurements taken hp Elman's methods for the
Ennerdalo and other forms.
429
O F THE ENGLISH LAKE DISTMCT.
It is evident that, if L. g h i t a l d i i be the parent forin, those races wliicli
approach it iiiost nearly in b h a p of head a i d in other respects may Le regarded
as iiiost nearly related, and comeclueiitly inore iwently beparated from it.
It is therefore of some interest to apply Eknian's sjsteni of i i i e a s ~ i ~ i ~ i e i i t
to races other than those of the Baltic region, and to see if by that tiieniis
any clue to their age may be found.
FIti,
3.
Limzocnlroius v~ucvto'usfponi Ennerdale, showing method of measurenient.
A. Bead-length. B. Head-height. C. Crown-level.
TABLE6.-Measurernents
of Liwizocalanus inacvwus and L. grimalilii.
Figurea ninrked
* are taken from Ekman, 1914.
Crownleyel.
Headheight.
------Ennerdale . .
. . . ... . . , . , .
U.S.A.--Green
- - ~ -
157
-26
131
126
- IG
110
137
+4.4
141.4
I -11.5
l"2.5
d
.,. .. 9
d
Insjon . , . . . . , . 0
3~eden-Malaren
,,
0
,
.. .. 0
134
. ,.,.. 9
140
Lalie
d
,,
,,
Lake Erie
1,alie C'anandaigoa
I
d
9
. .. . . . . . . . . .
9
-17
113
- 16
-13
1 I!)
118
I
d
Caspian Sea,
A&B.
R.
2.59
1
13.5
141
15.8
-
I
1
65*
-26r;
430
MR. It. GURNEY ON THE CliUSThUEAN PLANKTON
I possess a few specimen^ of L. yrimaldii from the C’aspian Sea which
were given to me by the late Canon Norman soine years ago, and by the
kindness of Dr. C’. Juday I have had the opportunity of examining
L.macrurus from Green Lake, Lalie Erie, and Lake Canandaigua (one of
the Finger Lakes east of Lake Ontario). Dr. S. Elrmxn also has been good
enorigh to send me specimens from Lakes Miilnren and Insjiin in Sweden.
Measurements of these races are given in Table 6.
So far as the numerical expression of the head-form goes, the Ennerdale
race cannot be coinpared with any of the Baltic races, since in none of thein
is 90 great a head-height accompanied by so low a crown-level. The only
race with similar liead-height (Lalie Mjiisenj has a dorsal swelling rising
above the horizontal dorsal line. On the other hand, the high, evenlyrounded dorsal outline rather closely resembles Ekinan’s figure of the race
froin Unden in Sweden, though that race has a crown-height according to
his measurements of only - 6. I t seems that in respect of this character the
Ennerdale race stands soniewhat apat t, but that it inust have been evolved
from the yirnaldii-type a t a con~par;itiveiyremote period.
The North American races differ but little in head-form, and conform inore
closely to the Baltic type. Both have a posterior inore or less horizontal part
with an anterior descending slope, arid agree very closely in appearance with
the Malaren forin, though the measurenients do not agree very well with
those given for that race (Pl. 23. fig. 6). But, as coinpared with the Ennerdale race (Pl. 23. fig. l), specimens from North Anierica certainly approach
far more nearly to the grimaldii type, and are consequently to be regarded as
of more recent origin.
This conclusion is strengthened by a consideration of the other characters
in which the two fornis differ.
(1) The true grimddii forin of the Arctic Ocean (examples from J a n a
River) nieasure over 3 mm., while the somewhat niodified form of the Baltic
inay also attain 3 inin. (Gulf of Finland). I t is, 011 the other hand, roughly
true of the Baltic area that the oldest fresh-water races are the sniallest
(Soinmen 1.87 mm., Unden 1 - 7 2 inin.). Stnnll size is therefore to s o n i ~
extent evidence of prolonged sojourn in fresh water. I n respect of this
character the Ennerdale race (2.113 inm.) holds a inore or less middle position.
The race from Lake Erie, 011 the other hand, is one of the largest known
(2.86 mm.), greatly exceeding any other fresh-water race and exceeded only
by those of North Siberia and the Gulf of Finlmd in salt water. The
Green Lake form, though similar io structure, is but lit,tle larger than that
of the Ennerdale race.
( 2 ) The antenna in the true grimaldii form reaches to the base of the furca
or even further (PI. 23. fig. 5 ) , whcrens i n typical 1,.nincruius it does not
extend further than tlie first ;ibdontinal segment. 111 this respect the Xnnerdale race belongs to the extreme fresh-water type, while those froin Korth
OF T H E ENGLISH LAKE DISTRICT.
431
Ainerica liavc the antenn:c ,slightly longer. Xu the Miilaren race, wliicli is
one of the m o s t primitive forms, the antennae in tlie female may reach to the
base of the furc:t.
(3) The longtli of the furcal rami in proportion to the whole body differs
in different lakes, hut the published iiiforination on this point is too scanty
to adinit of a definite conclusion as to whether there is any connection
between the shortness of the furca and the length of sojourn in fresh water.
Thc furcal rawi of the Ennertlale and the American forms are notably
shorter than those of the yritnaldii form froin the Caspian, but, on the other
haud, both the Milareii aiid the Insjiin races have these rami as long as or
longer than those of iny Caspian specimens.
(4) The pointed triauguliir forin of the lateral expausion of the last thoracic
segment has been given by Prof. Sars as one of the distinctive characters of
L. grimnltiii, since in a11 the fresh-wat,er races this segment is simply rounded.
I fiiid in m y Caspian Sea specinieiis that this segment is produced laterally
iuto a very well-defined point (Pl. 23. fig. 5 ) , and it is important to note that
a similar point is to be found in some of the specimens from Green Lake and
from Lakc Canandaigua, and ~ e i yrarely also in those froin Lake Erie,
while the Ennerdale race has tlie segment simply rounded. This character,
sinall as it may appear, seems to l ~ of
c importance in indic-ating relationship
with the parent forin, and tlie North Anierica!i race must for this reason also
be regarded as of compar;tt.ively rccent origin. The primitive Miilaren race
has this segment geiierally very slightly angular, and occasionally there is a
definite point as in L. griinaldii (Pl. 23.fig. 8).
I t is remarkable that, in spite of tlie coiisiderable differences in general
body-form between the brackish and fresh-water races of Liniizocaluncts,
there is no appreciable d i ~ e r e n c eto Le found between any of the appendagcs
of tlie two forms, except as regards the length of tlie iintennules. I have
coinpared the appendages of the seven races available to me, and find the
agreement perfect in almost every detail. There is, h w e v e r , one very slight
ditfereiice which may be peculiar to the Caspian race, namely the absence of
a spine on tlie outer distal angle of the first joint of tile esopodite in tlie
right fifth foot of tlie m:ile. Prof. Sars does not figure :I spine in this
position, neither was it present in a specimen examined by me, but it is
present in all other races of which figures are published.
Having dealt, so f a r as I am able, with the biology arid ctriicture of the
Ennerdale and North American races of Lii,zicoculanus in comparison with
others, there reiiiaiiis the consideration of the qurstion :i,s to whether these
races call be regarded as (‘ relicts” in the same sense as those of the Baltic
area.
I t must be admittetl that in neitlicr citse can any definile answer be given.
There can be little doulh that the whole of the Lake1;iiid area was
coinpletely covered by ice during the Glacial period, tliough the view that
432
MH. 11. G U R N E Y ON THE CRUSTACEAN PLANKTON
the lakes tlielnselves are glacially-eroded rock-basins is not universally
admitted. I n any case, however, the fauna must have reached these lakes
after tlie withdrawal of the ice.
According to Clifton Ward (1876) tlie passing of the Glacial period was
immediately followed by a submergence of tlie whole district by as much as
2000 feet, which would leave only the highest ground projecting as o
number of sinall islands in the iuidst of an arctic sex. If a submergence to
this or to a much smaller extent can be admitted, then L. ?nacvu?*usmight
well be a relict of this sea left in Ennerdale. Unfortunately Ward's
conclusions are not admitted hy geologists of the present day, though I have
not been able to find in any Merature availnble tjo me any serious discussion
of the question of pout-Glacial changes of level in this district. The matter
is hardly referred t o in M a d s ' Geology of the Lake District,' but
apparently he does not admit a submergence of more than a few feet', which
could not have made any inaterial difference to the distriLution of land and sea.
If a submergence to a n extent sufficient to bring the sea in the first
instance into direct connectiou with the Eunerdale basin cannot be conceded,
there are only two alternatives. Either the interpretation of the geological
facts is wrong: or a marine species has either been able to migrate for miles
up a rushing stream of fresh water or has been transported directly into the
lake. No biologist would for a moment consider such migration or transference to be even conceivable. It must be remembered that .we are dealing
with a species which occurs in this one lnlie only in the British Isles and
cannot have been transported to its present habitat from auy other lake in
Britain.
Even if Clifton Ward's great subinergence could be proved t,rue, it is still
a little doubtful if it would satisfactorily explain the facts. Our Irnowledge
of marine relicts seeins to point to the conclusion that tr~isformationof
marine species i n to fresh-wa ter relicts has rarely happened, and only in cases
where very large areas of water have been involved. ' h i s tlie L . mucrurus
of the Baltic area owe their origin to the transformation of the Yoldia Sea
into the Ancylus Lake, rather than to the separation of lalies from the Yoldia
Sea itself. In other wprds, L. yri~naltlii w:is transformed into a form of
L. wiaerurzts in h e Ancylus Lalie xiid not, in the first instance, in the
existing inland lakes. Similarly, we sliould not expect that a rare of
L. griinaldii could have survived in so sinall a lake its Ennerdale itself even
if it could be shown that t'he lake had itself been cut off from the sea.
To explain the occurrence of this species in Ennerdale in the same way as
its ~ccurrencein the Baltic lakes, it is inore reasonable to assume that the
Irish Sea itself has passed through a history somewhat siniilar to that of the
Baltic, having h e n chnnged from an arctic sea containing L. yrim11Zilii to a
fresh or brackish water, ant1 'finally to its present condition, a n d that during
tlie second phase L. pitni.ddi2' became in lmrt transformed i n the direction of'
L. ?nacrurus. Further, that conditions were such that, on the renewed
O F TIIE ENGLISH LAKE DISTRICT.
4%
~ntr:inceof salt water, immigratlion into Ennerdale was possible. I must
f r e e l j admit that such a supposition i s not supported hy the geologicd
evidence, but it does not appear to me to be a n altogether i i n p o d h
assuinptioii in view of t>hefollowing facts.
There is evidence of a subsidencc of land i t u m ~ d i a t e l yaEt,er tlie withdrawal
of the ice, and oE a later elevation at, a time when tlie subinerged peat-beds
and forests were formed. B u t the ;iniouiit of the latter elevation is uncertain,
and there is no positive evidence of a rise of more than 60 fret. O n the
other 11:iiid~tlie occurrence in Irelaad ( I f tlie Red Deer and Tieindeer seem to
necessitate the supposition that tliere was sonie land connection b e t ~ v e r n
England and Ireland iii neolithic time, and, as Jukes-Browie has poiiited out,
firstly i t is possihle that this elevation iiiay have heen greater than has been
supposed, and secondly i t is very probable tlint tlie floor of tlie Irish Sea,
wliich was tliicldy covered hy drift, has been greatly eroded aiid re-modelled.
It inay consequently have beeu a t so tnuch higher a level that :t comparatively
sniall elevation m:ty have sufficed to effect a land connection with partial or
complete damming off of tlie sea.
13r. Scharff has assunied the existence of a great lake occupying the
trough of tlic Irish Sea to explain tlie present distribution of the genus
C o r q o u t r s in Britain and Ireland, a n d it' such R lake could have originated
by freshening of a Glacial sea, not only might 1,.g ~ i n i a l d i have
i
been therein
isolated and transformed, but also dlysis oculuta could in this map have been
changed into JI.relicta aiid have reached its present station in Lough Neagli.
l'licre are two obvious objections, naniely that 111. re2icta does not live in
Ennerdale and L. m u ( ~ ~ t ~does
r u s not occur in Lougli Neagli. Pnrther, that
conditions which would :illow the latter to reach Ennerdale should also allow
i t to reach Wastwater aiid perhaps otlier lakes. To these objections not
inuch importance need be attached until niore is known of t,he conditions
which deterniine the distribution of fresh-water (lrust:icea. Not only does
tlie plankton of Lough Neagli differ radically froni that of the English lalrcs
in geiicral, bii t these lalres difler unaccountably among theniselves, aiid
TTastwzter a i d Ennerdale, alike as they seem to be i n physical condit~ions,
contain quite dif!ierent plankton. Hence i t cannot he assumed that a species
would establish itself in every lalie t o wllicli i t had access.
It is equally diflicult to explain the distribution of' LimnocaZu7lus in North
America. I t s distribution follows rather closely tliat, of' illysis relictu, as
shown in Table 7, page 434.
L. niuc'rurzis therefore occurs, in all tlie great 1;ikes and in L: number of
lalies belonging to the sitine drainage syst,em, but not, so far :IS I can find, in
any lakes outside this region.
S o far as the origin of tliese species is coiicerned, tlie view o i ~ c cheld that
the Great Lakes were themselves at one time invatled by the sea and that
111. relicts is a true relict within them has been generally abandoned, but a t
the saine time there appears to be 110 doubt that tlie sea did, a t a late stage
434
MR. R. GURNEY ON TIIE CRTJSTACEAN PLANKTON
in the post-Glacial history of the region, penetrate u p the St. Lawrence
valley and flood the basins of Iiake Ontario and of Lake Champlain. At
this time there existed an eastern outlet from Lake Huron through the
Ottawa valley. The marine deposits of this stage are found a t a height of
400-500 feet by Lake Champlain and at 600 feet near the east end of Lake
Ontario. I t would appear that we have here all the conditions necessary for
the isolation and modification of these two “ relict ” species, but thero are
Lalie Ontario
,,
,,
,,
,,
,,
,,
* . . .,. . . . .
Michigan . . . . . . . .
Superinr . . . . . . . .
Huron
..........
?
+
+
-
S t . Clair . . . . . . . .
Erie . . . . . . . . . . . .
+
..........
..........
+
+
+
+
+
Geneva
Green Lake
l‘he Fiirger Lakes :U:ina,nctaigua. . . . . .
+
owasco . . . . . . . . . .
Smeca . . . . . . . . . .
-
+
++
+
......
-
t
..........
Iieulia . . . . . . . . . .
Chgupa
Skaneateles
+
two great difficulties in the way, iinniely the absence of Jlysis d i c t a froin
Lakes Ontario and Champlain and the existence a t or before that time of the
Ningara Falls, which wotild be an effective bar to migration into the other
lakes. On the other hand, the absence of a species froin a lake a t the
present day does not necessarily prove that it has never existed there, and
the occurrence of both species in the Finger Lakes, which forin part of the
drainage system of Ontario, seeins t o be good evidence that they have
reached these lakes from Ontario. Their penetration into the other Great
Lakes must, one must suppose, have taken place by way of the Ottana connection, and in any case we are forced to assume for L. I I I U C T ~ I ~ a* ~capacity
.IS
for active migration up rivers which is denied by Elmian.
* S o far a8 I h o w , there is no published record of the occurrence of Liniizocalantrs in
Lake Ontario, but Dr. C. Judny informs me that he 118sfound it in n planlitoii eatnple from
this Inke token by Dr. I?. A . Clement in October 1922. I am greatly indebted to Dr Juday
for this information.
OF THE ENGLISEI LAKE DISTRICT.
435
Tile rehelit dihcovery of another species of the genus ( L .joliaiistwi, Marsh)
a tundra pool in A1:iska seeins to raise a new problern altogether. But
Biarali's description is very short, and it is not clear th:it t,liis new species is
really distinct from L. g~inzulu'iior L. i ~ ~ a ~ w i the
~ w os n, l j casential difl'cronce
nientioned being the shortiiess of the furcal rami. I t is important that this
species should be fully described and its distributioii ascertained.
iii
D I A P T O m S LATICEPS, ~ U Y S .
Syn. D. hircus, Brady.
Brady's sl)ecies, I ) . /tircus, was established in 3 891 on specimens taken
froiii Goats Water, au elevated tar11 on the slopes of Coniston Old Man.
There can be no doubt that his species is identical with 11. Zaticeps, from
which it diff ers in no esseat'ial charact,er.
It is an arctic and alpine species occurring inainly in Scandinavia, but
recorded fruiii Akniolinsk in Russia, the Julian Alps, Serbia, and
Herzegovina. It has also been taken in several lakes in Scotland and in
1rel:tnd.
The only lake in the Lake District in which the species is found is Hawes
Water, which is the highest of' all (694 feet), and for that reason inay have
a different teinperature. It seemed likely that 1).laticpps might be conii~oii
iii the high tarns of the district, but, as Z'have said in 1 1 1 ~notes on these
tarns? this is not the case. OK)the other hand, our lrnowledge of the fauna of
these t:irns is very incomplete, and it may prove to occur in the tarns of
Harter Fell arid to have reached Hawes Wilier from tlience.
CTCLOPS
ABYSSORUM, Sam.
This species has been found in all the lakes cxainined with the exception
of Ennerdale, Derwentwat,er, Bassenth waitc, and Eatliwaite. In Ennerdale
no liinnetic species of C 7 y l o l ~ swas seen in any of the s:iinples talien either
by Ur. Peawall or myself, but Brady has recorded the occurrence there of
C'. ricirivs. The occurrence of tliat species in the planliton of this district
seems most unlikely, and il, is inore probable that Brady had specimens of
('. a b y s s o ~ i , ~in
n , which case the species once inhabited Ennerdale but has
now disappeared.
Prof'. Brady has recorded the occurrence of this species in Windermere
and Coiiiston in deep water in Aug. 1883, and Prof. Sam, in his ' Cruatacea
of' Norway,' describes i t as iiiliabising only the deeper layers of water. My
own collectioiis in Wastwater and Coniston show that,, though it is found in
autumn 011 the surface, it is distinctly more abundant in deeper water, and
its absence f'roin Uerwcntwater, Baasenthwaite, and Estliwvaitt is no doubt
largely due to their sinall depth. It is replaced in these 1:ilics hy C. leitckartl.
In 1911 a few specimens wcrc taken by me in Bassenthwaite, but it is
evidently not an established iiiember of the plankton in that lake.
436
MR. R. GlTnNEY ON THE CRUSTACEAX PLANKTO3
The seasoual cycle of the species cannot be determined wit'h certainty
froni Dr. Pearsall's collections, which werc niostly taken on the surfam, ant1
therefore are unreliable in tlie case oE a deep-water species ; but :t careful
conip:irison of the records froni the different lakes leads to the conclusion
that there is only one period of breeding, naniely in Ihe autumn, and that
the adults die after breeding, the species passing the winter either in the
forin of resting-eggs or as nauplii. In all the lakes mature specimens were
rare or absent in spring and early suinnier, but were abundant in collections
made between August ant1 Noveinber. Fenides bearing eggs were found in
Hawes Water in August, but in the other lakes only in Septeniber or
October. If this is a true statement of the breeding cycle, it resembles very
closely the cycle in 1,.))1UcTU)'Us--niiotEier cold-water northern form. On the
TABLE8.-Measurenients
I
I
of Cyclops ul~ysso~*um.
I
Length Furca.
(including Per cent. Outerfiirca). of body. most.
1
- -- - - - I~
Wastwitter
Cruiumock
Conistoil
Ullswater
. .. ...
. .. . . .
. .. . . , , .
. .. . . , . .
1'35 m m
13 3
100
413
1.43
133
1)
402
1.44
13.7
1.42
11.6
IIawes Water . . . . 1.46
., .
.. , , . . . .
13.8
,,
),
))
394
388
~
1
8eta 3.
'er cent
,f body,
1
--
481
191
34.4
481
186
35.3
485
190
563
456
190
33
379
250
31
323
169
31
443
190
I
329
1
I
Windermere . . .
1.77
11.8
I,
316
Grasmere
1.68
14.9
1)
341
I
~
33.5
--
other hand, Sclieffelt (1908) and Burclrliardt (1900) found two breedingperiods in tlie Cyclops of the st~eizuus-groupstudied by them in the Black
Forest aiid Swiss Lalies respectively. It is not, however, clear with what
race or species these :iutEiors wme dealing, since the species of this group
recognized by Snrs and Lilljeborg as distinct have not been gencrally
admitted, and maiiy writers have followed Schmeil in including all within
the species C. strenerus. It seems certain that the three species C. lucustw's,
C. scutifw, and C'. ~ i c i t i i i sshould be maiutained. Whether C. abyssomm is
sufficiently distinct froiii C. strenuus as defined by Sars is rather more.
uncertnin, but the evidence goes to show that it is a lininetic and cold-water
representative of C'. stwuuus, which it is convenient to distinguish. It is
readily distinguished froni typical C. strelams by the greater length of the
nntennzc?of the furcal rmii, aiid of tjhe furcal sctz. The niuch greater
O F THE ENGLISH L14KE DISTRICT.
48 7
relative length of the innermost setn in C. u.byssorzm is per’haps t h e easiest
character by which the species may be separated, but Prof. Sars has
mumerated a nuniber of details uliereiii the species differ. It is to be hoped
that Prof. Sars’ limitation of these species will he followed, since i t i.; most
prob:i,ble tbnt they will be found t,o have different life-cycles and tliff’erent
habitats and distribution. The general adoption of Sch~neil’sdefinition of
C. strenuus has made comparison of stateinents with regard to these questions
nnrcliable and indeed valueless. So far as puldished information goes, i t
seems that (7. ulyssorunz is confined to northerii lakes, and is absent from
Swiss lakes, where apparently a form resenibling C. scutijer takes its place.
The Lalie District species is undoubtedly C. abyssomni, though the form
of the receptaculum_differs to some extent from Prof. Bars’ description and
agrees more closely with that of C. lacustris.
Those who ( e . 9 . Graeter, 1903j accept the species C. strenuus in its wider
sense lay great stress on its vm-iahility, and it might be supposed, if tlicir
view is corrkct, that great differences would be found betwcen individuals
from different lakes. This is far from being the case. I n general forin of
body-particularly
in the expansion of the last thoracic segment-there
is,
so f a r as I can find, no appreciable variation. I n size, in the length of the
furca and t h e relative length of the furcxl wtz there a r e differences, I)nt
they a r e not great. I n Table 8 I have given mensurements of individuals
from seven of t>helakes. These are, in the case of the first four, averages
from tell specimens, but in the remniiider of from two to six.
It will be seen that thc srnallcst specimens are from Wastwater and the
largest from Windermere and Grasmere, which is hardly according to
expectation. Those from t h e “ primiiive ” lakes agree in having t,he longest
s e w , together with rather long furca, but thc longest furca is found in
Grasmere. The differences are, however, by no means sufficient to bridgct
the gap between C. streimus a n d C‘. nbjssorum.
It is rather remarliable t,hat the colour of‘ the Lal&lld individaals is
commonly a very pronounced yellow. The species has not, i n fact, a t all the
general appearance of a limnetic form. but rather of a n i n h : ~ ~ ~ i t aofn tp 1 d s
: r i d ditches.
( :YCLOPS YEKITSTUS,
Xormuu
(C. Sisott.
S p . C. ciinitcts, Graeter, 1908.
( ~ y c l o p renzrstiis
s
was described i n 1906 * froin specimens taken from
~ n a r s h yground on Exmoor. It has since heen found by Mr. I). J. Scourfield
on Exmoor and Dartmoor, and hy 1110 in the Bog of Allen, near Newbridge
i n Ireland. It appears to be a species confined to lime-free waters. and may
I)e included among what may be c:ilIed the Sphagnophil Entomostraca, such
as d cantholebr ris ctrrrirostris, Chjltlorirs piS9er,BIomria bvet*&es, etc.
*
Crustacea of Devon and CornwalI,’ p. 180 (London, 1906)
438
MR. R. GURNEY ON T E E CRUSTACEAN PLANKTON
The description given by Norman and Scott is not altogether complete,
inasmuch as no mention is made of the peculiar marlrings 011 the integunirnt,
which are quite distinctive, and the allusion to the swimming-feet as being
similar to those of C. vernalis is misleading. I t secins therefore advis:ible
to supplement their description to some extent.
Thc most characteristic feature of the species is t.he very pronounced
crenulation of the niargins oE the abdominal segments and (to a less extent)
of the last thoracic segment. The surface of the integnnient of the thorax
is niarked by delicate s t r k which give it the appearance of being minutely
wrinkled, while the surface, both dorsal and ventrill, of the abdominal segments is either striated or ornamented with lines of minute pits similar to
those found in C. diuplianits. Thcse pits seem to run, a t least on the dorsal
surface, on the crest of low ridges, which can be distinctly seen in side view.
The furcal mini are provided, as i n C. &ridis, with cilia on their inner
margins, but these cilia are in groups and do not form a cont,inuous
fringe. Usually the anal opercnlum is very prominent.
The swimming-legs differ marlredly froin those of C. zw*nalis not only in
their more robust form, but also in the number of spines and set= 011 the
terminal joint of the outer rainus (see Table 9). But C. vernalis is subject
to some variation in respect of the number of spines, and it is not unusual to
find individuals with a spine-like formula of 3.4.4. 4.as in ('. venustus ; but in
these cases the number of setw is not increased. C. vernalis also resembles
C. veiiustus in frequently having the cut,icle of the abdominal segnients
pitted. The two species are, however, quite distinct, the form of the furca
alone sufficing to distinguish them, apart froin the differences in the form of
the swimming-legs and the excassive pitting of the cuticle in C. venzistw.
The resemblance to C. capillatus, Sars, is somewhat closer. The antennx
are 12-,jointed in each species ; the form of the receptaculum and the 5th leg
is closely similar, and the spine- and seta-formula of the legs is identical.
On the other hand, the legs of C. capillatus are distinctly more slender, and
the furcal rami much more elongated and smooth on their innnr edge.
Further, though the abdominal segment.s show a slight toothing of the
posterior margins, this is not pronounced, and I have not been ahle to detect
any surface pitting in speciinens froni Norway which I collected many years
ago in the Romsdal.
There remains for comparison the specins described by Graeter in 1908
under the name of C. cdrinitzis. M. Chappuis has been kind enough to send
me a mounted specimen of' this species, and a n examination of this specimen
and of the published descriptions of Graeter and (Jhappuis convinces me that
the two species are identical. They agree in the following characters,
wherein they differ froin most other species :(1) Antennule of 12 joints.
(2) Furcal raini short, slightly divergent, with groups of cilia on their
inner edge.
439
O F THE ENGLISH LAKE DISTRlCT.
(3) Median seta of the fiircal rarni of unnsnnl length.
(4) Outer seta of the furca of hnlf (c?*initics)* or scarcely inore tlinn half
(aenusfus) the length of the inner seta.
(5) Swiinoiing-legs with the same spine- and setn-formula t -a forinula
only found otherwise in
capillatus, Sars.
(I.
Graeter states that the abdominal segments are jagged a n d that the surface
of the cuticle is pitted over the whole body, hut I have not been able to see
this in the specimen, owing,' no doubt, to its transp:irency.
Since Grader's name is later than that of Noriiiari and Scott, I hare
tlierrfore regarded it as a synonym of C . wizustiis.
I t is evident that this species and ('. vii*idis are very closely related, ns ha.:
already been pointed out hoth by Graeter and hy Chappuis, but they are
certainly distinct.
This species was found to be not uncorii~non in & " " ~ / ~ a p upools
m
near
Greeiidnle Tarn and on Floutern Pass.
TABLE9.--Showing
spines and s e t 2 on last joint nf the exopodite
in species of the C. airidis-group.
-
~
-
~
l
Leg 1
:3
)
~.
4
4 : :
5
4
4
3
4
4
4
4
SZDA
CRTSTALLTNA, 0. P.Mitell.
B. o.ystal/ina is a littoral species not properly, or :it least generally,
belonging to the l)lanktcrn, thougll f recluently recorded :is occurring in o p i i
\later. I n tlic Ldic of Gencv:~, Lake C'oi110, Ldre Maggiore, and otlier
* I n the specimen which I have exmined this seta is more than hnlf the length of the
inner seta, and so agrees completely with C. oeiutstus.
t 111 the specimen at m y disposal it is impossible to corint the spines and set= with
certniiity on all legs. 1have given in the table only those whicli ere beyond doubt.
420
nm.it.
GURNEY ON THE CRUSTACEAN PLANKTON
large Swiss lakes, however, it appears to be a regular ineniber of the
plankton, arid Burclihardt has described the form there found as a distinct
species-8. limnetica, characterized chiefly by the absence of a nnchal organ.
In the Lake District it was found in small numbers i n tlie majority of the
collections froin Derwentwater, so that it may probably he regarded as really
liinnetic there, wheieas the few records of' it from Bassenthwaite may be due
siinply to migration from the littoral region. The sanie is thc case with
Estliwaite and Grasmere. On the other hand, my csperience of night
collecting in Ennertlale seems to show that this species, though reniaining
in the littoral region during the day, may take to the open water at night.
(See p. 482.)
All the specimens froin tlie Lake Distikt, were of the typical form, with
well-developed nuchal o r p n .
HOLOPEDIUM
GIBBERTM, Zaddach.
The distribution of IIoZope7etdiuna in the Lake District is somewhat peculiar.
I t is recorded by Beck from Easedale Tarn (915 feet) and from Windermere,
and it also occurs in Qrasmere (P. A. Buxton, Sept. 1912) and Rydal Water
(D. J. Scourfield). In Ullswater it was foand in Sept. 1912 and on Aug. 20,
2920, but not in any other collection made by Dr. Pearsall. I n Ennerdale
it was present in very small numbers in three out of seven collections taken
by him, but was abundant in my own collections in Sept. 1922. .So far as
is known a t present it does not occur in any other lake in the district.
Ensodale Tarn, Qrasmere, Rydal, and Windermere forin part of the same
(lrxinage system. The fact that it has SO rarely been taken in Windermere
lnnv possibly be due to its being occasionally carried into the Inlie, but not
becoining establislieci there ; but it is more probable that it is not uniforinly
distributed in the lake, and also that, being a deep-water form, i t is not
taken in surface phnkton. I n Ennerdale it is fairly evenly distributed in
both shallow and deep parts, but it is rare on the surface during the daytime, preferring deep \\ ater. At night, however, it is abundant on the surface.
This preference for the deeper layers of water does not appear to be
gellerally characteristic of the species, since ScheEelt (1908) states that it is
foulld at the surface at all times; but he also found it to be unevenly distributed and to occur in swarms. Lilljeborg notes the same thing in
Sweden.
I t is generally regarded as a " Glacial relict," being confined to northern
regions or to cold water.
The yeinis DAPHMA.
The increase of knowledge of local and seasonal variation among the
litnnetic Daphnias has led to the general recognition that any division into
well-defined species is impossible. All are therefore regnrded as belonging
to one species, 1). Zonyispb~u,within M. liicli an alniost infinite numLer of
-.
subspecies,” varieties,” :inid ‘‘ forms ” have heen described. I (lo uot
propose to discuss the question of the sy st.ernatic arrangement of t1ie.e
Daphnias, but it seeins to nie that the enlargement of the significance of t’lie
11;\111e I).
Zoqispir~nin this sense Ins serious disndvnnt:iges, and that tlie
suggestion of Langhans that a new name, D.wriabilis, should be introduced
to iiiclndc the whole series OF thrsc. varia!)le Duphnias might with admiitage
be adopted. The question can, however, hardly be regardeJ a3 6 tinlly
settled, and, for tlie present, it is iiiore satisfactory to acceilt Lilljehrg’s
long is pi^?^, Iiyalina, and cucitllatu, whilst fully recognising that the three :we
nirited by transitional forms.
All tlie lininetic D:iplinias 01‘ the 1:ikes belong to the “ species ’’ ligcdir?a
with its “ subspecies ” gcileatu :dl~ccnst~)*is.Beck lias recorded the occurrelic0 of I,. ocoilluta (under the name Ifyalotluphrtiu beroli/ieitsisj, but this
species lias been seen in tlie district by 110 one else, and it is probal)le that
lie was mistaken. Dapltnia is :tbs+iit altogether from IVastwater and
Ennerdale Water, mcl apparently ;LI.<Onormally from B:issenthwait,e. There
:ire none from the latter lake either i n Dr. Pcarsall’s collections or my o w n ,
and Rlr. Scourfield informs me t h t he : L ~ Ofailed to find it there. On t,he
other hand, Miss Pratt records hoth 1). p i i l and
~ ~ I ) . lon,qispinn as occ-urring
in April 1898, so that apparently sonlo spccies occtirs there a t times. As
Bassenthwaite rect:ives the overflow from Derwerit>waterwhich contains an
abundance of Dnphnia, it is very rem:~rkablcthat the same f o r m skioultl not
establish itself in B:issrnthwaitr.
The distrihution of the diEort1nt f o r m of Duphniu in the district seelris to
hear little or 110 rulxtion to the h i n a g e system. While Riit8terniereand
(Irnrninock, which wrre originally united into one lake, botli contaiii tile
t,ypic:d
hyyalim, which occurs in these 1:tBes only, the Ikqd/uk/, of
Esthwaite i s quite clifterent from that of Windermere, into which Estliwsiite
drains, and the same form, 11. ytrleuta, inlialits \TTindermere and Coniston,
which are not connected in any way.
/-
n.
DAPHNIAHYALINA s. str., in Butterinere and Crummoclr.
In the form from these two lnlies the front of the head is usually very
nearly straight or slightly concave (test-fig. 3, A) : but it is very variable,
and may occasionally be distinctly couwx as in I). /wlZticidu. In a collection
made on Sug. 27, 1920, seyernl specimens were seen with the front of the
forin shown in text-fig. 3, €3. An rxactly similar varidy i s i1lustr:itctl by
Lil1,jeborg (1900, pl. xv. fig. 4) a4 “ , f o m i a rrvtiwtrlis nzo~st~osa.” It is
characteristic of tlie (hummock Daphnias that the shell->pine forins a considerable angle with the body axis-from 20’-40”.
Although I r e p r t l this
form o f I)apliniu as properly referablt1 to 1).hyalinn s. str., Lilljeborg, i n
some respects the population is transitional on tlie one hand to [). Zutwstris
and on the other i o
pellut+la.
n.
LTNN. J0PRN.-ZOOLCGY,
YOL. Y S S V .
3‘1
442
NR. R .
wmm
nN THE CRUSTACEAN PLANKTON
I n a plankton sample of Sept. 1912 a single specimen was met with which
obviously helongs to I ) . yaleata (text-fig. 8, C). I (lo not think that this
specimen can be regarded as a sport or mutation froin D.Ayyalina, but rather
as an instance of the transport of an ephippium from Coniston or Windermere. IF this be so it goes to sliow that these lakes are not so isolated as
would appear, and t,hat,intrrchange of species is not infrequent. Tf, in spite
of such interchange, t,he Daphnias inhabiting the different lakes remain
distinct, it is evident that the local races are established by right of survival,
and it, leads one to suppose that., di&cult as they may be to separate, yet they
may represent fixed species. Our conception of species is deterniined inaiiily
by oiir ability to discriminate individuals hy fixed and measurable standards ;
but not only are physiological differences largely ignored or are unmeasurable,
hit two races separatetl on1.y ty niinimnl niean differences may be just ;IS
real specific units as those distinguished by obvious characters i n all individuals. The evidence goes to show that a, single lake as a rule is inhabited
by one race of limnetic .l)aplmia only, and, although within such a race
extreme forms are commonly found, it is obviously of no use to give these
variants names, as has frequently been done in the past. But, with tliat
exception, i t seems advisable in t'he present. state of knowledge to recognize
all well-marked races as distinct rather than to treat all as variants of one
collective species. The question of real Fpecific distinction cannot, I think,
be determined by laboratory experiment,, neither is the fact that the winter
forms of L number of Daphnias can he shown to be morphologically
identical prove anything more than close relationship.
If the many
forms of 1)aplmia are to be regarded as variants of one species originating
under the influence of external condition?, the reappearance in widel!separated areas and m d e r conditions which can hardly lie imagined to he
identical of precisely the same form-e. g. I ) . yaleatn in Winderinere and i n
Clentwl Asia-is difficult or impossible t,o understand. It must, be admitted
that the whole problem of specific validity is raised b j the genus B a p h i a irl
its acutest form, and is f a r from heing solved.
DAPHNIA
LACPSTRIS, Sa)*s.
1. Esthwaite and Hawes R a t e r .
The Daphnias of Esthwaite illwtrate reniarlrably well the impossibility of
drawing any definite distinvtion between the various fornis now grou1,t.d
within the species I).Zm~yis/tina. Wliilr some individuals talien in Esthwaite
in July 1921 were indistinguiahable fro1111). longispiria forms yosea, having
the crest interrupted over the eye and the general forin of that species, tile
usuaI type of f)uplt)zia present in t1i:it and in other collections helongs to
I / , 11pli1mvar. lacusti&. I was a t first inclined t o suppose that two distinct
races were preseiit, but the tws forms glade so completely one into the other
that they must hc regarded as one. The outline of the head may b2
coii:pIeteI~rounded, or niay show :t scarcely noticeable dorsal angle, while j l l
.
otherd, and esprcially in young speciincns, this angle is lroduced into :I
siiiall papilliforin projection. The crest is generally continuous over the eye,
hut is often so inconspicuous as to be seen with clificdty, while soluetinles it
is interrupted as in U . h y i s p i m ~
An exactly similar h ~ h / t z (JC'C111'9
' ~
in Hawes Water, but in such sn~all
nutnbers that I have not had niucli material for esaininat,ion. Nearly ti11 tlic
specimens seen have the head quite rounded, but occasionally there is a
slight trace of the dorsal angle so often seen in Esthwaite spccimens,
This form seeins to be the same as that which is found in Loch Leven and
Loch Lomond in Scotland, and was described by Richard (1896, p. 307) as
U. Zacust& var. ricina, with the escel)tion tllat the posterior $ p i n ( b in tile
Lalie District forni is usually directed inore or less dorsally.
444
MR. It. GURNEY O N THE C R I X T A C E A N PLAYKTON
Burclrhardt’s P. h p h l folma Iitceyrzerisis fro111 the Lake of Lucerne is
evidently the same variety. I n one individual from Esthwaite the dorm1
projection of tlic head is tlenticulate as figured by Rurckhardt for his fornia
jzi rwsica.
I Jer wen tma t p r .
The Daplinias from Derivelitwater rather closely resemble 1).Iigalirra s. str.,
hut should, I think, rather be included in U . laczcstris by reason of the
concave front and rather liiglicr head. The dorsal angle characteristic of
thc form froin Esthwaite and Nawes Water is occasionnlly, but very rarely,
seen in Derwentwater.
DAPIINIA
C;ALEA1’.4, S’
tll’S.
The typical form of B. galrata occurs throughout the year in Coniston,
I
Winderinere, and Ullswater, being most abundant in the former. Although
Dr. Paarsall’s samples cover every seasoii in the Scar, I have not found
ephippial females in any of them, SO that the species appears to be acyclic.
The same appears to be the case with the B. Zacustris of Esthwaite, Hawes
Water, and Derwentwater, but in Cruinmocli’and Buttermere there is a
distinct sexual phase in D.hyuliua in October, though, even here, the species
persists through the winter.
Daplinia-Seasonal Variation.
The material a t iriy disposal does not admit of any positive statement with
regard to seasonal variation of form, but such variation is very slight if it
occurs at all. With regard to D.galeatu, in which it could most easily be
detected, I have found on the one hand crests equally as high in winter as in
summer, and individuals with a quite round head in J u l y and August. I
have no doubt that a sinall variation of head-form, and of size of hody, could
be shown statistically with sufficient material, but the variation is certainly
not so proriounced as to be appreciable to the eye.
I n this respect also the plankton of these litkes differs markedly from the
Danish and Central European lakes, and approaches the nortliei~~i
type.
BOSMINA
OBTUSIROSTRIS, Xars.
The identity of the northern races of B. caregoni with these occurring in
the alpine lakes is now established, and, according to Riihe, the united species
ahould be known iinder the name of B. coyegoni-loiigislvina. As, however,
the naiue B. loyispincr has generally been used in a inore restricted sense,
:ind is so used by Lilljeborg, and as the name B. obt,usirostris has been
universally used for the northern Eornis wilh short niucro, I prefer to retain
i t in Lilljeliorg’s sense.
1 ti the Lake District this species occurs, often in great ahundance, in nearly
all t,lie lakes. Its apparent! abseiice Ironi Butterinere may be due to the fact
that the collections were made from the shore only ; but,, although a single
specimen was fouiid in Bassenthwaite in October 1921, it is certainly not
established there.
It would he of interest to ascertain if there are any coiistant differeiiws
between the Bosniinas of the diff'erent lakes, but this can only be doiie satisfactorily by measurements of large numbers of specimens carried out 011 the
system laid down by Burckhardt,, and my niaterial does not :idniit of such
treatlnent, since the necessary number of well-preserved sl"hieiis j,s n o t
available from all the lakes at the same seasons. Since tlierc. is verv great
wriability within the populatioIi of a lake with regard to length of ant,rnn:i
and of n~ucro,t,he selectioii of single individuals for nieasurement or
illusiration is likely to be n~isleading, but it is not entirely without value,
-~.i\\.initerniere
Esthmaite
. . . . .I
,
., . . . . . .
310
328
21. vii.
3 . ix.
1Jerwei:twatt.r . . . . 17. v.
.
Ullswater , . . . . . . 1.vii. ,
' IInwes Water . . . . 11. rii. 1
Coniston . . , , . . . , 6.vii.
81
390
430
9;'
~
Ennerdale . . . . . . . . 28. ix. ,
Witstwater.. . . . . . . 30. ix.
I
1 Cruinmock. . . . , . . . 12. vii.
I
I Flouter11 Tam . . . . 37. ix.
Goats W a t e r . . . . . 3. x. '
.
393
543
505
327
490
,
I
~
45
152
123
38
~-
and a table of nreasurement.s of individuals chosen as being so far as could
be judged typical of the population is here given. The example given from
Esthwaite is above and that) from Erincrdale below the average size, but
typical of form. This: table shows that the Bosininas of the two primitive
lakes Chunnnock and Wastwater are not only very much larger than all
others, but have longer uiucro and antenna (text-fig. 3 , U). On the other
hand, those froin Ennerdale, which inight be expected to be similar to thosse
froin Wastwater, are, in fact, conspicuous for their very short antenna and
inucro and are not particularly large. Herein is another strong point of
difference hetween these two apparently similar lakes. In the remainder
of the lakes the differences shown bet>ween t,be Bosrninas are not, I think,
outside the limits of their ordinary variation witliin a single population.
Thc specimens froni Floutern Tarn and Goats Water are not only the
~ii~allest,
]Jut I ~ v rLe
e shortest iniicro.
For the reasons given ahove I have also been unable to study the seasorial
variation. I have, it is true, made a n attempt to do so with material from
Couibton, but the numbers available and sufficiently well preserved are not
enough to give R satisfactory result. They teiid to show that there is a
variation, but that it is very sinall.
The species is found at all tiiiies of the year, and. except, in Wastwater
and the tarns, t8hereseem to be no pronounced sexual periods. Ephippial
females have been seen in collections from Windermere (Sept aud Oct. 1921),
Crummock (Oct. 1921), Uerwentwater (NOT‘.1921), and Wastwater (Sept.
and Oct. 1921 and 1922). In Wastwater alone do ephippial females form
any considerable proportion of the population. On Sept. 30, 1922, 31 per
cent. of females were ephippial, but not a single male was seen. I n Coniston
a i d Ullswater tliere seems to be no sexual phase.
BOSMINA
LONGIROYTRIS, 0. E: M r r l l .
This species only occurs in Esthwaite and Grasniere, both beiiig lakes of
the “evolved ” type; but., whereas it appears to be the only species of
l’osmiiu in Grasmere, in Esthwaite it is found in company with U . obtusirostris, an unusual association which is also found in Lough Neagh and has
been commented on by Uakin aiid Latnrche.
Miss Pratt states that it was common in Bawenthwaite in 1898, but it, was
not found in any of Dr. Pearsall’s collections from that lake. Miss Pratt’s
list of Crustacea froin Basvenlhwaite differs in so ni;inj respects from my
own that one can only conclude that conrlitions must have clianged very
greatly since 1898.
The Esthwaite forni is quite typical, but in Mept. 1921 +.heantenns of the
adults were found to Le unusually short, and many were even of the lorui
described by Lilljeborg under the name of B. breviwr7iis Hellich. It
appeared in the collections first in April and increased in numbers till June.
I n July nuinbers decreased, and in August it was very rare. I n September
it was agaiii present in abundance, and large numbers of’ feinales bore
ephippia. It was not toimd in collections made in October and November.
LITERATURE
REFERXED
TO.
BECK,C.-On some new Cldocera of the Eaglisli Lakes. Journ. R. Dlic. Soc. (3)iii. 1883,
p. 777.
BIRQE,E. A . -Plankton Studios on Lake Mendota. 11. Trails. ll.isc. Acad. xi. 1898,
p. 374.
BBADY,
G. S.-Notes on the Crustacean fauna of the English Lakes. lntellectual Observer,
xii. 1868, p. 416*.
BRADY,
G. S.-British species of Entomostracri belonging to Bapkain aiid other allied
genera. Nat. €list. ‘Trans. Sorthd. and Durham, siii. 1898, p. 317.
*
I have not been able to consult this paper.
BURPKHARDT,
G.--l'auuistische
und syatematische Studien iiber das Zooplankton der
griisseren Seen der Bchweiz iind itires Grenzgehietes. Rev. Suisse Zool. vii. 1899.
I)ARIN, W. J., and I,ATARCWW,X--'l'he I'lankton of r,oiqh Neugh. Proc. It. Irish h a d .
xxx. 1913.
EIINAN,S.-Studien iiber die marinen Nelikte der riortleiiropaischeii Binnenge\vasser.TI. Die Variation der Iiopfform bei Ll?nnocalanus gvimaldii ( De Guerne) uncl
I;. rnacrumy, Sars. Int. Rev. Ges. Hydrob. mid Aydroz. vi. 1914, p. 335.
GRSETWR,&k.-Die Copepoden der Uiiigehng roil Basel. Bev. Suisse Zool. xi. 1903.
GRAETER,E.-Ein nener Hijhlencopepode C~~clups
c r i m h s , n. sp. Zoul. Anz. xxxiii. 1908,
p. 45.
MARR,J. E.-The Geology of the Lake District. Cambridge, 1916.
MILL. €1. R.-Rathymetrical Surve:; of the English Lakes. Geog. Journ. iv. 1894, p. 237 ;
vi. 1895, pp. 46 Lk 138.
NAITIIANN,
E.-Ueber die natiirliche Niihrung des limnischen Zooplanktons. Lunds Unir.
krsslrrift, N.F. Avd. 1,Rd. 14, nn. 31, 1918.
PRARRAJ.L,
W. H.--The aquatic vegetation of the English I d e s . Journ. of Ecology, viii.
1920, p. 163.
I'IARSAI~L,W. €1.-The development of vegetation in the English Lakes considrred i n
relatioil to the general evolutioii of Glacial lakes and rock-basins. Proc. Coy. Soc.
ser. B, xcii. 1921, p. 2.59.
~ ' R A T T ,E. M.-The
Entomostraca of Lake Bassenthwaite. Aim. Mag. Nat. Hist. (7) ii.
1898, p. 46.
RICHARD,
J.-Revision des CladocBreu. Ann. Sci. Nltt. Zool. (8) v . 1896.
S(-HEFFELT,
E. Die Copepoden und Cladoceren des siidlicheii Schwarzwaldes. Arch. 1'.
Ilydrob. iv. 1908.
SCOWLFIEI.~,
I). J.-Synopsis of the Icnomn species of British fresh-water Entomostraca.
,lourn. Quek. Nic. Club, (2) viii. 1903,p. 631.
n'ann, J. CLIFTON-The Geology of the northern part of tile Engh:h Lalie Tlistrict. &in.
G d . Surr. London, 187ti.
\ V , \ R ~IT.
. TI.-A biological reconnaissance of some elevated lakes in the Sierra3 and
Iloclties. Trans. Amer. Mic. SOC.s s v . 1904.
\Voi.rrI.:tticcic,
R-Die nstiirliclie Niilirung pelagisclien Clidocer~iiund die Rolle des Zeiitrifupenplanlitoiis in Siisswuserr. hit. Kev. ges. TIytlrob. ~ i n dIIydrox. i . I9!ltc?
1'. 871.
ISSPLAN.ITION O F I'I~ATE 23.
Liirznoccrkmts iiincrui~us,Sars.
Fig. 1. Side view of female from Ennerdale Wntrr.
2. Fifth leg of fenial~.
3. b'ifth leg of male.
4. Oiiter bralich of right fifth leg of male.
5. Side view of female froin the C'~ispianSea ( L .pi?)zaIdii),
6. Side T. iew of inale from 1,nlte Erie.
7. Head of feinde from Insjon, Sweden.
3. Side view of last thoracic sc.gnieiit of male froin 1,altr Rlalaren, Hn-eden
CRUSTACEAN PLANKTON
JOURN. LINN.SOC.,ZOOLVOL. XXXV. PL. 23.
FROM
THE E N G L I S H LAKES.