88
I(. I
S
: CONTRIBUTION TO OUR KNOWLEDGE OF MALLOMONAS
A contribution to our knowledge of Mallomonas. By KATHARINE
HARRIS,B.Sc.,
University of Reading
(Communicatedby Prof. Tom HILRRIEI,F.R.S., F.L.S.)
(With 90 Text-figures)
[Read 5 February 19531
ABSTRACT
This paper gives general observations on four species of M d h n a s . The chromatophore
is single in all, but deeply divided into two lobes. The bristles are always hinged and
readily movable. The following new features are described : in M . leboimii, the cyst; in
N . lychenensis, the shredding of the scales and growth of small individuals; in M . teilingii,
the stages leading to cyst development and in M . intemnedia var. gesticululzs var. nov.
the structure of the scale and various growth and reproductive stages.
Two internal parasites, 1 Protozoa, are described, one on M . teilingii and one on
M . intermedia var. gesticululzs. These are of importance in destroying a population and in
forming cysts which have been mistaken for Mallonzrmas cysts, one forming the basis of
a new species of Mal-bmmm.
INTRODUCTION
I have studied the genus of Mallomonas of the Chrysomonadales for several years, largely
from the systematic point of view. During this time I have made the general observations
which are described in this paper,
Samples were collected daily or at longer intervals, in ordinary glass bottles; it was
found that most species could live in such bottles for several days provided they were
kept away from bright light. As a rule the water was centrifuged before examination,
and this seemed to have no ill effect on the Mallomonas.
In order to study the scales, cells were dried on the slide and examined both dry and
mounted in a medium of high refractive index. I found piperine +antimony tribromide
the most satisfactory mountant. Certain species such as M . lychenensis, which do not
collapse on drying, were disintegrated with chloral hydrate, in order to separate the
scales. For this purpose a minute crystal of chloral hydrate, on the tip of a needle, was
added to a nearly dry film containing a living specimen.
When giving measurements in describing a species, I have tried to limit myself to
individuals which I consider mature. However, I know no way of distinguishing mature
from nearly mature individuals, so the lower limit of dimensions is liable to be somewhat
arbitrary.
GENERALNOTES ON SELECTED SPECIES
Mallomonas teilingii Conrad (Conrad, 1933, pp. 45, 63)
My specimens agree closely with the description already given, except that the rear scales
are about half the size of the anterior scales and that the chxomatophore is single with
two lobes (Fig. l),not double.
Season: November to April, most frequent in February and March. Cysts in February
and March.
M . teilingii is fairly common and has been found in twelve different ponds near
Reading, occurring in some of them year after year. Most of these ponds are small ones
overhung by trees, all occur on agricultural land or by roadsides, some are permanent
and some dry up in summer. It has not been found in large lakes or on acid soil. In one
closely observed pond it lasted for about 6 weeks, then encysted and disappeared until
the following year.
I
Fig. 1. M . teilingii. Figs. 2-5. M . intermedia var. gesticulans. Fig. 2. Mature cell. Fig. 3. Bristle
tips. Fig. 4. Cyst in mother cell. Fig. 5. Scales. Figs. 6-8. M . leboimii. Fig. 6. Mature cell,
rather small specimen. Fig. 7. Conrlexion between chromatophore lobes further enlarged.
Fig. 8. Cyst. x 1000, except Fig. 7.
90
K. HARRIS: CONTRIBUTION TO OUR KNOWLEDGE OF MALLOMONAS
Mallomonas intermedia Kisselew var. gesticulans var. nov.
Diagnosis. Differt ab M . intermedia in apicibus nitentibus setarum angustioribus,
acutioribus, et in hypnospora punctata.
Differs from M . intemnedia in having bristles with narrower, more acute apices, and in
the dotted wall of the cyst.
Additional characters : length usually 2 0 4 0 p, rarely larger, scales usually 5-6 y long
by 3.5-4-5 p wide, cyst 1f5-17 p diameter, round, pore small, posterior, rim not prominent.
M . intermdia is incompletely known from Kisselew’s (1931) account, but Lund (1942)
described specimens,which he identified with it, more fully, and I accept the identification.
I presume that Kisselew’s figure of the arrangement of the scales is inaccurate, especially
as regards the two ends of the cell. The chromatophore, described by Kisselew as single,
and by Lund as double, is single and deeply lobed (Fig. 2). The cyst in var. gesticulans
has a posterior pore (Fig. 4), the position of the pore is not given for the Type by Lund,
and has widely spaced not very conspicuous pits.
It should be noted that there are several distinguishable strains of M . intermedia in the
Reading district besides var. gesticulans. They occur in ponds of other types from the
ponds which have var. gesticulans, and at different seasons, and show minor, but constant,
variations from the Type in the scale, bristle tip, in general appearance and in cyst.
Var. gesticulans has only been found in five ponds near Reading but reappears annually.
All these ponds are small ones on agricultural land and are partly overhung by trees.
One of them dries up each summer. In one closely observed pond var. gesticulans
appeared, swarmed and encysted and disappeared in about a month.
Season: February to June, encysts March to June.
Mallomonas leboimii Bourrelly (see Bourrelly, 1947 ;
and perhaps M . sphagnicola Nygaard, 1949)
The identificationof my specimens was confirmed by M. Bourrelly. They agree perfectly
with Bourrelly’s account but I saw a few larger specimens, up to 85 p long. The cyst
(Fig. 8) has not previously been observed; it is smooth, spherical, 28 p diameter with an
inconspicuous posterior pore. The chromatophore is single, deeply divided into two lobes
(Figs. 6, 7).
M . leboimii has only been found in two groups of ponds, both containing Sphagnum,
on acid peaty soils and not overhung by trees. One group of ponds dries up in summer.
Season: December to May, most common February to March, cyst found in February.
Mallomonas lychenensis Conrad (see Conrad, 1938, 1941 ;
Bourrelly, 1947; also var. tesselata Nygaard 1949)
The Reading specimens (Figs. 9-16) agree well with those described by Conrad and
Bourrelly, but I have noticed a range in the form of the pore of the cyst (Figs. 10-12),
which sometimes approaches Nygaard’s var. tesselata, e.g. Fig. 11. This range is certainly
not due to variation in the maturity of the cyst. I believe that there are a,number of
strains of this species occurring in different ponds.
I am able to add a little to the understanding of the anterior scale, which looks so
different when seen in the living cell from when isolated on the slide. Fig. 14 shows an
anterior scale which has been slightly damaged, so that the transparent semicircular plate,
which usually stands out from the scale (see anterior scales in Fig. 9), is seen lying beside
it in the same plane. It appears that this plate is attached at right angles to the scale
along one side, and is not easily seen when the scale is lying flat on the slide.
M . lychnensis is very common indeed around Reading, and is found in a large variety
of ponds on different soils, but not in large lakes. It has been found in every month of the
year except September, but is most commonly seen in February and March. Cysts may
be found in every month when the species occurs and may persist in the water for weeks
I(. HARRIS : CONTRIBUTION
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OUR KNOWLEDGE OF MALLOMONAS
91
after the motile individuals have disappeared. I n one closely observed pond it appeared,
swarmed, encysted and disappeared three times between February and July, when the
pond dried up. I n other ponds I believe it only makes one appearance in the year.
STAGES
IN THE LIFE CYCLE
No one seems to have kept Mallomonas successfully in culture, though it will often
survive, in slowly diminishing numbers, in a bottle of pond water for a week or two,
occasionally more, even showing a certain amount of development. My description is
based on a series of observations of M . intermedia var. gesticulans taken from a pond a t
intervals of a day or two, and is supported by scattered observations of other species.
The study reveals such a variation in the size and shape of the cells and the distribution
of the bristles that one asks oneself whether there is any possibility of confusion of one
or more species. I do not think this is the case. The material was taken from a wellstudied pond which had been examined from time to time €or years, whose flora was well
known and contained no mature individuals, other than those of var. gesticuluns, to
which the young stages could belong. Intermediates were seen between most of the stages,
and some of the changes took place so quickly that they could be observed in a single
individual on the slide. There is certainly a risk that some of the changes may have been
hastened, or brought about, by the bright illumination or other condition of examination,
and where this seems likely I have mentioned it in my description.
Stage 1. Earliest appearance. Mallonaonm must be present in the pond as a cyst before
it appears as a flagellate, though I have never been fortunate enough to see the germination of the cyst. It seems likely that, after germination, it is present in the water as an
ill-characterized soft-bodied Chrysomonad, for a t the beginning of the Mallomonas season
one may often see such an individual developing scales a t its anterior end (Figs. 18, 19).
These scales are normal in shape, rather delicate and may have bristles or not. The
posterior end of the cell is a t first naked, but later produces scattered scales on the surface
of the protoplasm. Such forms intergrade with the normal M a U m n a s (Figs. 18-21).
I have seen similar forms in M . leboiwtii (Fig. 17) which, being large, shows this stage
particularly well, also in M . lychenensi,s (Fig. 16), and in M . acaroides Perty var. tatrica
Woloszynska (1939), M . doignonii Bourrelly (1951), M . heterospina Lund (1942), and in
two undescribed species.
The Mallomonas may be present in the water in the early and mature stages in small
numbers, for several weeks. It frequently seems to be intermittent in a particular pond,
possibly because it is a small and shifting population. It increases, gradually a t first, and
later rapidly, to a climax which may be called swarming. The method of increase during
this early period is not known.
Stuge 2. Liberation of the probplast. This occurs in a medium-sized cell. Numerous
contractile vacuoles form a t the posterior end of the cell, spreading later to the sides and
anterior end. The protoplast seems to move in its shell as large contractile vacuoles form
and disappear (Figs. 22, 23). The protoplast then withdraws itself from the ends of the
cell and collects in a spherical mass t o w a r b the middle (Fig. 24). Such a sphere is then
liberated through a break in the armour (Fig. 25) or by the complete break-up of the
armour. This process was watched on many occasions and was seen also in M . lychenemis.
The escaping protoplast was about 12 p in diameter, with two or four chromatophore
lobes, and might have or not have a flagellum.
Sometimes the armour broke up before the protoplast had formed itself into a sphere,
and the contents poured out forming an +regular mass of protoplasm surrounded by
large contxactile vacuoles. On one occasion I watched such a mass round itself off and
develop a membrane. It is interesting to compare this with accounts given by Conrad
(1914) for M . mirabilis and Carter (1937)for M . anglica ofthe liberation of the protoplast
in an amoeboid condition. Their figures resemble the appearance of the protoplast as I
saw it, but I did not see any pseudopodia, such as Conrad describes. I did not watch the
92
K. HARRIS: CONTRIBUTION TO OUR KNOWLEDGE O F MALLOMONAS
Figs. 9-28. For legends see p. 93.
K . HARRIS: CONTRIBUTION
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KNOWLEDGE OF MALLOMONAS
93
protoplasts for more than 20 minutes, nor did I keep them in a hanging drop. Except
for these accounts I should have attributed the pouring out of the protoplast from the
cell t o some abnormal condition, precursor of death, but in the light of that work, and
of the single example described above, I am inclined to reserve judgement.
At this time the water was f d of many stages of var. gesticulans, including naked
protoplasts with two or four chromatophore lobes and with or without a flagellum, or
rarely with two flagella. There were also protoplasts which showed a few scales a t the
anterior end, and all stages from this to the round oval Mallomonas cell covered with
scales (Figs. 26-28). I have no direct evidence that one of these stages developed from
another, only the presumptive evidence of intermediate types.
Stage 3 . Longitudinal division. Longitudinal division has been described by Carter
(1937)for M . anglica. I saw it in several species, including M . allorgei (Deflandre) Conrad,
M . lychenensis, M . akrokomos Ruttner, M . acaroides var. tatrica, and it usually took
10-15 minutes. The following account is based on M . intermedia var. gesticulans, and the
figures represent a single individual over a period of 10 minutes (Figs. 29-34). As a rule
the nucleus and chromatophore divide before the flagellum. In this case only two chromatophore lobes were visible at the beginning, and it is possible either that the other two
were obscured from view or that the chromatophore divided later. The scales in the
dividing cell looked loose and irregular, and some bristles came off and floated away as
I watched. As division proceeded new scales formed on the line of fission so quickly that
the protoplasm was never seen without them, and as the daughter cells separated new
rear bristles appeared like viscous threads being drawn out. The scales of the daughter
cells were regular and closely fitting, but I do not know how they were related to the old
ones. No new anterior bristles appeared while I watched.
Stage 4. ‘Small Ovals. ’ The smallest of these cells was 10 x 7 L,L (Figs. 35-37), and all
sues were present between this and ordinary mature cells. Fig. 35 shows what I think
is a n early condition of this stage, showing scales only a t the anterior end and suggesting
that it has arisen from a soft-bodied Chrysomonad. The scales of these ‘Small Ovals’ are
similar to the mature scale but smaller and more delicate (Fig. 38), and two chromatophore lobes were present, whether joined or not was not observed. These individuals seem
to grow into ordinary mature cells, but it was impossible to tell whether a n intermediate
cell such as Fig. 39 had developed from a ‘Small Oval ’ or not. ‘Small Ovals ’ occur only
at the swarming period of var. geaticulans and have not been observed in any other
species, possibly because they closely resemble the ‘Small Spheres’ and may in some
species be indistinguishable from them.
Stage 5. ‘Small spheres. ’ These are spherical motile cells from 8 to 13 ,LL in diameter
with small delicate scales (Figs. 4 0 4 2 ) . They are distinguishable from the ‘Small Ovals’
only in their shape. They may have either two or four chromatophore lobes. The specimens of M . lychenensis, shown in Figs. 49, 50, may represent this stage and I have also
seen it in M . acaroides var. tatrica.
I saw one ‘Small Sphere’ of var. yesticuhns burst, liberating its contents, which
immediately divided into two parts which rounded off forming two non-motile protoplasts (Figs. 4346). This process was observed many times in M . acuroides var. tatrica,
the two new protoplasts always showing characteristic markings a t one end. This process
must be regarded with reserve and may be an abnormal one leading to death. Clearly,
however, the presence of four chromatophore lobes suggests that division is imminent and
Figs. 9-16. M. lychenensis. Fig. 9. Mature cell. Figs. 1&12. Cysts. Fig. 13. Body scales.
Fig. 14. Anterior scale damaged so that silica plate is i
n same plane as scale. Fig. 15. Rear
scales. Fig. 16. Immature cell. Fig. 17. M. Zeboimii, immature cell. Figs. 18-28. M . intermedia var. gesticulans. Figs. 18-21. Inmature to nearly mature cells. Figs. 22, 23. Figures
from same cell preparing to liberate protoplast. Fig. 24. Spherical protoplast ready for liberation. Fig. 25. Liberation of protoplast. Fig. 26. Naked protoplast with two flagella. Figs. 27, 28.
Protoplasts producing scales. x 1000.
49
Figs. 29-47. M. intermedia var. gesticulam. Figs. 29-34. Stages in longitudinal division taken from
the wane individuel. Figs. 35-37. ‘Small Ovals.’ Fig. 38. Scale of ‘Small Ovals’. Fig. 39.
Intermediate size between ‘Small Ovals’ and mature cell. Figs. 40, 41. ‘Small Spheres.’
Fig. 42. Scales of ‘Small Spheres’. Figs. 43-46. ‘ S d Sphere’ liberating its contents which
divide, taken from same cell. Fig. 47. Precyst stage. Figs. 48-61. M. lychenewis. Fig. 48.
Shedding of the scales. Figs. 49, 60. Small individuals. Fig. 61. Precyst stage also showing
shedding of the scales. x 1000.
K. HARRIS : CONTRIBUTION TO OUR KNOWLEDGE OF MALLOMONAS
95
the immediate separation of the liberated protoplast into two parts suggests that it had
actually divided before it left the cell armour. The two protoplasts seen in Fig. 46 bear
a resemblance to the young cell in Fig. 35.
Stage 6. Precyst stage. Individuals o f var. gesticulam, stages 1 to 5, were all abundant
during the first 10 days of the swarming period. After this they became relatively rare
but the mature ones became more abundant, and the average sue of the population
gradually increased. Large round leueosin bodies, associated with strings of globules,
became very conspicuous and four chromatophore lobes were often present (Fig. 47),
see also Fig. 51 of M . lychenensis and Fig. 52 of M . teilingii.
Stage 7. Cyst formation. Cyst formation was studied most fully in M . teilingii (Figs.
52-58), but follows the same course in id1 species. The membrane of the developing cyst
is formed within the protoplast of the mother cell and the protoplast passes into it
through the pore, which in M . teilingii is anterior. This type of reproduction is common
among the Chrysophyceae, and has been observed for Mallomonas by Carter (1937).
As the protoplast passes through the pore it is surrounded on the outside by a covering
of foamy cytoplasm full of small contractile vacuoles (Fig. 55). The membrane of the
incipient cyst usually becomes thickened early and may show the mature ornamentation
before the protoplast has entered it (Fig. 55), but in other cases the membrane remains
thin until after the contents have entered it and the thickening and ornamentation
presumably occur later (Fig. 57). Fig. 56 shows an intermediate condition.
The fully formed cyst may contain two or four chromatophore lobes (see Fig. 58, of
M . teilingii with two lobes and Fig. 8 of M . leboirnii with four lobes). I was not able t o
see whether the lobes were joined. The nucleus was not observed, but Conrad (1914)
noted two nuclei in the cyst of M . mirabilis.
PROTOPLASMIC STRUCTURE
A number of features can be distinguished in the living Mallomonas cell.
The flagellum arises from a small granule which is situated outside the main protoplasm of the cell. This is the ‘perle’ of Hourrelly & Chadefaud (1951). The large nucleus,
occasionally showing a nucleolus, is usually seen at the anterior end of the cell but is
sometimes centrally placed.
The chromatophore is single, deeply divided into two lobes by clefts a t the front and
rear ends, and in the mature cell is folded round the central cavity of the cell. This is true
of all the species which I have examined, some twenty-five. The two lobes may be broad
and spirally twisted, completely enveloping the cell as in M . teiliwii and M . intermedia
var. gesticuluns (Figs. 1, 2), or they may be straight as described by Bourrelly (1951) for
M . doignonii. I have seen individuals of M . doignonii where the chromatophore lobes are
narrow and almost strap-shaped so that they only occupy one side of the cell. I n an
immature cell the chromatophore may be smaller (compare Figs. 6 and 17 both of
M . leboimii, and see also Fig. 16 of an immature M . lychenensis). The two lobes may be
joined only by an exceedingly narrow bridge of coloured plastid material which is flanked
on either side by specialized but colourless protoplasm. This is shown in Fig. 7 for
22. leboimii and has also been seen in another undescribed species of the same group.
Contractile vacuoles are usually situated in the cleft between the lobes and in the space
between the free edges of the chromatophores as well as in the extreme rear (Figs. 2,
6 and 17).
This description may be compared with the study of M . insignis by Bourrelly & Chadefaud (1951) from which, however, it differs in the interpretation of certain features.
THE TRIPAR~TE S C ~ EAND BRISTLE
Two of the species described here have a scale which I have called (tripartite’. There
is a large group of species which have this type of scale, including M . intermedia
and its varieties, and M . leboimii, M . acaroides and M . tonsurata Teiling. The scale
(0
59
Figs. 52-58. M . teilingii. Figs. 52-51. Stagesin cyst formation. Fig. 58. Cyst. Figs. 59-66. M . interw d i a var. gesticulam. Figs. 59-63. Tripartite scale. Fig. 59. Isolated scale. Fig. 60. Damaged
scale showing detatched flange. Figs. 61, 62. Longitudinal section of scale and bristle with foot
in different positions, diagrammatic. Fig. 63. Reconstruction of scale, diagrammatic. Figs. 64,
65, 66. Dried individuals showing arrangement of scales. Fig. 66. Half of bristle only shown.
x 1000 except Figs. 59-63. Figs. 59, 60-62, x 2000, Fig. 63, x 4000.
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K. HARRIS : CONTRIBUTION TO OUR KNOWLEDGE O F MALLOMONAS
consists of three parts here called the ‘shield’, the ‘dome’ axid the ‘flange’. Fig. 63 shows
a diagrammatic reconstruction of the scale, Fig. 59 shows the isolated scale as seen on the
slide, Fig. 60 shows a scale in which the dome has been lost and the flange has become
detached but lies beside the shield, and Figs. 61, 62 show, diagrammatically, two
longitudinal sections through the scale. The shield is a roughly triangular plate of silica,
slightly thickened a t the edges and somewhat hollowed on its outer side. The dome is a
hollow silica hemisphere projecting obliquely outwards from the shield and forming a
conspicuous knob in the profile view of the cell. The base, or ‘foot ’, of the bristle comes
in contact with the dome, to which it is held, probably by protoplasm, which acts as
a hinge and renders the bristle capable of active movement. Sometimes the whole foot is
in contact with the dome and sometimes only its tip (Figs. 6l,62). These details may often
be seen by focusing on the scales a t the anterior end of M . intermedia var. gesticulans or
M . bboimii (Figs. 2, 6 and 17). The flange is a delicate silica margin along the two sides
of the shield farthest from the dome. It projects obliquely inwards in the intact armour
and is entirely covered by the shields of the neighbouring scales. I n a dry preparation
the dome and flange appear darker than the shield and may for this reason be thought
to be thicker, but this dark appearance is due to the angle a t which the light strikes the
oblique surface, and not, I think, to the thickness of the silica.
In M . intermedia var. gesticulans and 31.leboimii the bristle, as has been seen, is joined
to the scale by a movable hinge. This hinge is not as clear in all species as it is in those
with tripartite scales, but I believe it must exist, in some form, in all bristle-bearing
species, since all are able to move their bristles actively. The bristle movements are most
striking, however, in the larger species with tripartite scales, and M . i%termedia var.
gesticulans was so called because of the way in which it moved its bristles. In a motionless
cell most of the bristles radiate, while in a quickly moving cell most trail, as though
passively; in both motionless and moving cell, however, one or more bristles may point
in a different direction from the rest. Movements are most obvious in such bristles and
a forward-pointing bristle may move slowly from side to side as though acting as a
feeler. I n a stationary cell caught in bits of debris, one sometimes sees a bristle change
its position, moving through an angle of 90” in a second or so. Pig. 4 shows the armour
of the mother cell with regularly radiating bristles, and may be compared with Figs. 2,
17 (stationary cells) or 21 (moving cell) where the living bristles cross each other and some
of the forward-pointing might be expected to show active movement.
A few species of Mallomonas possess spines which are quite distinct from bristles, being
prolongations of the scale margin, and immovable.
SHEDDING
OF SCALES I V MALLOMONAS LYCHENENSIS
M . lychenensis and a small group of allied species, including M . allorgei and M . anglim,
have scales which do not overlap but are joined a t the edges to form a rigid armour.
Carter (1937) has described how M . anglica renews its armour from within, leaving
fragments of the old armour adhering to its outer membrane. The same process may be
seen in M . lychenensis, sometimes a single scale or group of scales is shed and sometimes
the whole armour is thrown off (Figs. 48, 51). The process occurs chiefly during the
swarming season, probably because this is a time when cells change their shape rapidly,
either by growth in length or by the development of leucosin bodies within the cell.
I have seen the same sort of shedding of scales in another species (undescribed), of the
same group, and should expect it to occur in M . allorgei which however is not common in
this district.
SCALE ARRANGEMENT
The scales of the Mallomonas armour vary in size and sometimes shape, according to their
position on the cell, and will be referred to as the ‘anterior’ scales, immediately Smrounding the flagellum, the ‘body’ scales, Over the greater part of the cell and ‘posterior’
scales, a t the extreme rear.
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K. HAJUZIS : CONTRIBUTION TO OUR KNOWLEDGE OF MALLOMONAS
The anterior scales may differ more or less from the body scales and are a useful
diagnostic feature. In M . teilingii they differ only in bearing bristles, being indistinguishable in size and shape from the body scales, in H.lyckmmis the anterior scales are
highly specialized in shape and are the only scales to bear bristles, while in M . interd i a var. gaticulans and in M . leboimii they tend to be slightly larger than the body
scales, the domes point forwards instead of across the cell (Figs. 65, 66), but they show
no sharp distinction from the scales immediately behind them.
The anterior scales are the first to be developed in the soft-bodied Mallomonas of both
stages 1 and 2 (Figs. 16-19, 28), and may develop to their mature size even in quite
small cells (Figs. 49, 50) in certain species, while in other species they remain comparatively small in the immature cells as in M . intermedia var. gesticulam.
The body scales are the most easily seen of all the scales and therefore the chief
diagnostic feature. They may be nearly uniform in size all over the cell as in M . Eychenensis
(Figs. 9,48-€iO), or they may be larger in front than in the rear as in M . intermedia var.
gesticulam.
The rear scales are minute and may form a group sharply differentiatedfrom the body
scales, both in size and shape, as in M . lychenensis, or they may intergrade into the body
scales as in M . i n t e d i a var. gesticulans. They are too small to have much diagnostic
value.
PARASITES
Mallonurnas is subject to a number of parasites. The two which I have studied are of
importance because they may devastate a population and because certain infected
individuals have been mistaken for normal stages of MauonzOnas development.
Parasite of Mallomonas intermedia var. gesticulans
In warm weather in early June large quantities of M . i n t e m d i a var. gmticulum, infected
by a parasite, were found in a shallowpond. Samples ofthis pond were examined daily for
6 days, by which time nearly all the Mallonzonas and the parasite had encysted. Almost
the whole population was devastated by this parasite, only three or four normal cysts
being found among many hundreds ofparasite cysts. In another pond, some weeks earlier,
and in cooler weather, a few early stages ofthe parasite were found on the same species of
M d h 7 u t s . Here the attack proved abortive, only the early sbges and no cysts being
observed, while the Ndlomonas developed normally.
A similar parasite has been observed on another strain of M . intermedia (undescribed).
Teiling (1946, pp. 70 and 86) gives a figure and description of a ‘dauerspore’in M . elongata
Beverdin which I believe to be a parasite cyst allied to the one described here.
The parasite was fist seen as a colourless nearly spherical zoospore which swam up to
the Mallomonas, always an immature specimen, and sought to attach itself with rapid
jerky movements, the rear ofthe parasite being in contact with the Mallomonas (Fig. 67).
This stage was not observed in detail, and only a few examples were seen. A n early stage
of infection is seen in Fig. 68 and here the parasite is a long oval colourless organism,
narrowing to a neck where it is attached to the host. The parasite cytoplasm passes
through the cell armour into the cytoplasmic lining, where it spreads. keeping outside the
chromatophores. Later it spreads outside the armour as well as inside it, obliterating the
scales and bristle bases (Pigs. 69, 70). It seems to spread mostly towards the rear of the
cell, and when the parasite cytoplasm reaches this end it grows inwards between the lobes
of the chromatophore and forms a coarsely granular mass (Figs. 71, 72). The finely
granular cytoplasm on the outside of the armour now withdraws into the cell, where the
parasite grows, gradually filling the space and digesting the chromatophore. One t o three
parasites may attack a single host. When nearly full-grown the parasite forms a round
or oval body surrounded by a thin wall (Figs. 73, 75). From this stage three types of
development appear to be possible.
Figs. 67-80. M . intermedia var. gesticularw infected by parasite. Fig. 67. Motile parasite attacking
Mallomonas cell. Fig. 68. Two attached parasites spreading outside chromatophores. Figs. 69,
70. Parasite spreading all through cell and oitside armour. Figs. 71, 72. Parasite forming
granular maas at base of cell. Fig. 73. Immature parasite cyst. Figs. 74, 75. Mature parasite
cysts type I. Fig. 76. Isolated parasite cyst type I. Fig. 77. Empty shell of cyst type I.
Fig. 78. M a l l o m o m armour vacated by parasite cyst. Fig. 79. Parasite cyst type 2; with
non-motile reproductive bodies. Fig. 80.. Parasite cyst type 3, with motile reproductive bodies.
x 1000.
c2
100
I(. HARRIS: CONTRIBUTION TO
OUR KNOWLEDGE OF MALLOMONAS
Type 1. The commonest type of development is for the protoplasm to contract away
fiom the thin wall and form a second thicker wall, after which it contracts a little further
leaving a space a t both ends (Figs. 74,75). Both this space and the one between the walls
appear to be fullof water. The protoplasmic mass is closely packed with refractive granules
and shows one or two brown bodies in the middle, which are the remnants of the chromatophores. The inner wall and its contents form a sporangium which is liberated, leaving
the outer wall inside the Mallomonas cell wall (Figs. 75,78). The fate of the sporangium
is unknown but occasionally, a t any rate, it bursts, liberating its contents, since a number
of empty shells were found in the water. Three small colourless spheres and the remnants
of the chromatophore were found in one of these empty shells (Fig. 77).
Type 2. In a few individuals the protoplasm, after forming its fist wall, divides into
a large number of colourless spheres. These were observed to escape as non-motile bodies
(Fig. 79). Their further development is unknown.
Type 3. I n a single individual the parasite, after forming its first wall, gave rise to six
actively motile zoospores which moved rapidly round the cavity. They remained enclosed
for about 10 minutes when the individual was lost. It was impossible to see their
flagellum (Fig. 80).
It would be reaaonable to regard types 2 and 3 as sporangia furnishing soft-bodied
reproductive units for rapid reproduction. The possibility also exists that one or more
differentparasites may be present and produce different types of sporangium.
The parasite of Mallomonas teilingii
A few infected individualsare usually to be found in any large population of M . teilingii,
and occasionally the parasite becomes epidemic and may destroy the greater part of the
population. I first mistook this parasite for a stage in the life history of M . teilingii, and
the mature cysts have been described by Nygaard (1949) under the name of M . tridentatu.
He did not, however, see the early stages of development, and from a study of this and
comparison with the normal cyst development, it is clear that the condition is an
abnormal on0 due to a parasitic infection.
The first sign that something is wrong with the cell of M . teilingii is shown by the
breaking and folding of the chromatophores, the presence of one or more groups of
granules in the cell, and the division of the cytoplasm into two or more parts. Fig. 81
shows this, each of the three portions into which the cell is divided has a central body
which suggests a nucleus, but I hesitate to call it one. As the condition advances granules
collectin groups in the rear divisionsof the cell ;the front division is usually free from these
granules (Fig. 82). The apparently uninfected portion at the anterior end then becomes
separated from the rest (Fig. 83), and the infected portion forms one, two or three ovals
or spheres according, probably, to the number of infections (Figs. 84,85). Each sphere
or oval consists of a central mass of granules surrounded by broken portions of the chromatophores, which may become disk-shaped and be interspersed with scattered granules.
There is no rigid wall as yet round the parasite. When three spheres are present they may
be arranged as shown in Fig. 85, or in a single row. The anterior portion of the cell
remains separate with an active flagellum and frequently contains a leucosin body at its
base. The infected portion now elongates and surrounds itself with a thick wall of the
shape shown in Figs. 86-88 which may be called the tridentata cyst. The anterior portion
of the original Mallomonas may die, as shown in Fig. 86, or may continue to live. Fig. 89
shows this portion attached to an empty Mallomonas armour from which the tridentata
cyst has escaped, and Fig. 90 shows it escaping from such an armour. I have never seen
the condition with two or three infections develop beyond the stage shown in Fig. 85,
but I have seen the infected portions burst the armour and escape at about this stage,
and I think it possible that they may continue their development in the water.
A very similar parasite attacks M . heterospina, but as I have not seen the resting cyst
I cannot say whether it is the same species.
I(. HARRIS : CONTRIBUTION
1'0 OUR KNOWLF,DOE OF MALLOMONAS
101
Nygaard (1949, p. 135, fig. 71) shows an incompletely described species referred to as
N.sp.I, which, from the figures, appears to be infected by a parasite of the tridentatu type.
No cyst is shown, but the shape of the anterior portion of the cell contents of several cells
recalls Figs. 83 and 84 of M. teilingii.
, r e -
"\I
I
89
Figs. 81-90. M . teilingii infected by parasite. Pigs. 81-85. Stages after infection. Pigs. 86-88.
Mature cyst. In Fig. 86, the M a l l m n a s protoplasm has died; in Fig. 87 it is still active. Figs. 89,
90, escape of remnant of Mallomonas protoplasm.
I think that both the parasite of M . intermedia var. gesticulans and of M . teilingii need
further study before they can be classified. In both, the chromatophore is taken into the
body of the parasite and this is distinctly a feature of a Protozoa rather than a unicellular
fungus.
SUMMARY
1. Certain aspects of the ecology,structure and life history of four species of Mallomonas
are described.
2. M . intermedia Kisselew var. gesticulans var. nov. and the cyst of M . leboimii
Bourrelly are described.
102
K. HARRIS: CONTRIBUTION TO OUR ENOWLEDUE OF MBLLOMONAS
3. The chromatophore in all four species is single and deeply lobed.
4. Several stages of the life cycle of M . i n t e r d i a var. gesticulans and M . lychenensis
Conrad are described (someof them seem to be new), and also cyst formationin M . teilingii
Conrad.
5. The tripartite. scale and bristle attachment, and also the movement of bristles, are
described for M . i n t e d i a var. gesticuhns.
6. The scale arrangement is described for X . intemzedia var. gesticulans and M . lychenensis Conrad, and the shedding of the scales for M . lychenensis.
7 . Two internal parasites are described, one affectingH.interm.edia var. gesticulans and
one affecting M . teilingii.
REFERENCES
BOURREILY,
P. (1947). Alges m e 8 et nouvelles des mares de la For& de Fontainebleau. Rev. gdn. Bot.
54, 309, 310.
BOURRELI;P,
P. (1951). Une nouvelle espbce de Chrysomonadine: Malldoigrronii. Bull. SOC.
bot. Fr. nos. P 6 , 156.
BOURRELLY,
P. & CELADEFAUD, M. (1951). Sur les oaractbres d’un Mallontonas et les &init& des
ChrysophycBes. C.R. A d . Sci., Paris, 232, 434-435.
CARTER, N. (1937). Pseudomallomonas anglica. New Phytol. 36,57.
C o r n , W. (1914). Contributions & 1’6tude des Flagellates. I. Stades amiboides et palmellaires chez
Mallomrmas mirabi2is nsp. Arch. Protwtenk. 34, 82-89.
CONRAD,W. (1933). Reviaion du &nre Mallontonas Perty (1851)incl. PseudomaUMnona8 Chodat
(1920). Mdm. Mus. Hist. nat. Belg. 56, 1-82.
Co-,
W. (1938). Notes Protistologiques. Bull. Mus. Hist. Nat. Belg. 14, no. 20.
Co-,
W.(1941). Flagellates d’une mare d’hdennes. Bull. Mus. Hist. Nat. Bdg. 17, no. 39.
IEL8S-W,
J. A. (1931). Zur Morphologie einiger neuer und seltener Vertreter des pflanzlichen
Microplankton. Arch. Protistenk. 73, 237, 238.
L m ,J. W. G. (1942). Contributions to our knowledge of British Chrysophyceae. New Phytol. 41,
274-92.
NYGAARD,
G . (1949). Hydrobiological studies on some Danish ponds and lakes. 11.K. danske videmk.
Sekk. Skr. 7,no. 1.
TEILING,E. (1946). Zur Phytoplanktonflora Schedens. Bot. Nother, H. I,61-88.
WOLOSZYNSKA,
J. (1939). Die Algen der Tatraseen und Tiimpel. Acta SOC.Bot. Polon. 16, 1.