<cialogical Journal ofthe Linnean Suciety ( 1984), &
239-259.
I
:
With I 1 figures
Spicule dimensions as taxonomic criteria
in the identification of haplosclerid
sponges from the shores of Anglesey
Mi. CLIFFORD JONES
School of Animal Biology, University College of North Wales,
Bangor, Gwynedd LL57 2UW
The lengths and widths of at least 100 spicules from each of 126 specimens, comprising at least 12
species of haplosclerid sponges, mainly from Church Island and Rhosneigr, Anglesey, North Wales
have been measured. It was found that spicule dimensions by themselves would be unreliable in the
identification of species. T h e sample means, medians and maxima, when plotted using width and
length axes, form specific clusters that overlap, sometimes to a considerable extent. T h e correlation
coefficients for width against length varied widely, even when single species were considered. The
variation arises from differences in the numbers of juvenile spicules in various samples. T h e best
correlation coefficients exceeded 0.8 and the regression constants for linear correlation in such
samples could be useful in the diagnosis and taxonomy of the species. The coefficients of variation
for length and width also yielded parameters for species characterization. In general the coefficient
for length tended to increase as the mean length increased, whereas that for width tended to
decrease with increasing mean width. Some species stood apart from the general trends, however.
T h e coefficients varied widely from one sample to another of the same species, identified using a
variety of diagnostic features. T o some extent the variation was linked with the date of collection.
When all the data were combined, the average coefficient for width decreased markedly in May.
The same was true for two species that were separately considered. T h e decrease was not simply
caused by a change in mean width, changes in standard deviation also being involved. There was a
tendency for certain species, in particular Reniera rosea and Gellius ungulutus, to produce thin spicules
in the spring, which became incorporated distally in the primary spicule bundles in July-August.
KEY WORDS: Sponges
Porifera
~~
-
Haplosclerida
-
spicules
CONTENTS
Introduction .
.
.
Materials and methods.
Results
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
Number of spicules measured per specimen.
Maxima, means, medians, modes and minima
Correlation coefficients and regression lines.
Coefficient of variation
. . . . .
Frequency distributions .
. . . .
Discussion .
.
.
.
.
.
.
.
.
.
Acknowledgrmcnts
. . . . . . .
References.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
. . . . . . . .
.
.
.
.
.
.
.
.
of the frequency distributions .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
239
242
243
243
245
247
249
253
255
257
.
.
258
.
.
INTRODUCTION
The Haplosclerida is a difficult group for the taxonomist (Burton, 1926b;
Bergquist & Warne, 1980) mainly because haplosclerid spicules are usually of
+
0024-4082/84/020219 2 I $03.00/0
239
01984 The Linnean
Society of London
240
W. CLIFFORD JONES
one type only, namely oxeote megascleres, and they vary in size, shape and
arrangement, even in the same specimen. Not infrequently styli and strongyli
may occur, but these are probably imperfectly formed oxea. Microscleres (toxa
and sigmata) are found in some species, for example Gellius ungulutus (Bwk), but
either one or both types may be so reduced in numbers as to be virtually absent
in some specimens (Burton, 1948). The megascleres are joined together by
spongin to form a three-dimensional reticulation, which can vary in the
regularity of the meshes, in the number of spicules abreast in the spicule bundles
and in the relative amount of spongin (Burton, 1926a). When one adds the
general plasticity of form and surface texture evinced by some species and the
variation in colour, it is not surprising that difficulty may be experienced in
identifying specimens and in classification.
I n an attempt to sort out the haplosclerid sponges living in the vicinity of
Bangor, North Wales, I have studied the skeletons of over 125 specimens
collected mostly at low water spring tides and fixed immediately after removal
from the substratum. The identification of species was facilitated by the fauna
lists for Roscoff (BorojeviC, Cabioch & Ltvi, 1968), Plymouth (Russell, 1957),
the North Sea (Arndt, 1935) and Ireland (Stephens, 1912, 1916; van Soest &
Weinberg, 1980). Bowerbank’s treatise ( 1866, 1874, 1882), although
antiquated, has also been consulted and descriptions of the species by Topsent
(1887, 1891) have been of great value. I n addition to identifying the local
species, it was hoped to determine the range of variation in spicule dimensions
per species, a t least for those identified using a variety of diagnostic characters,
not skeletal alone.
Spicule dimensions have traditionally been given in descriptions of sponges.
I n recent times, commonly the maximum, mean and minimum values of length
and width have been separately recorded, when it would have been more
helpful to know the width of the longest and the length of the narrowest
spicules. Ltvi (quoted by Griessinger, 1971) suggested that in Renieru cruteru the
spicule volume might be constant, longer spicules tending to be thinner and
shorter ones stouter. However, Griessinger (1971) was unable to confirm this for
the Mediterranean renierids and haliclonids. More recently the standard
deviations and standard errors of the means have been stated (e.g. Fry, 1970;
Rutzler, 1981), also the coefficient of variation for length (Griessinger, 1971) or
both length and width (Hartman, 1958). The coefficient of variation (standard
deviation x 1OO/mean) is a dimensionless indicator of variability. Frequency
distributions of spicule lengths in specimens of Ophlitaspongiu seriuta have also
been compared using in particular the Kolmogorov-Smirnov non-parametric
test by Fry (1970).
Hartman ( 1958) calculated the coefficients of variation for 100-spicule samples
of Huliclona cunuliculata and obtained values of 5.8 (length) and 16.7 (width).
Griessinger ( 1971), using 150-350-spicule samples, obtained values of 8, 8, 9
and 1 1 for four other haliclonid species with mean spicule lengths of 90, 1 10, 150
and 245 pm respectively. These species had spicule networks ranging from ‘very
regular’, through ‘regular’, then ‘confused’ to ‘dense and confused’. It seemed
that the coefficient did not reflect closely the skeletal arrangement, but was
better correlated with spicule size. However, he stressed that these tentative
conclusions required to be confirmed. For the styli of Hymeniucidon perleve Stone
(1970a) discovered that the coefficients varied with the month when the
specimen was collected. The coefficient for length ranged from 17.6 to 28.4 and
SP1CUL.E DIMENSIONS IN HAPLOSCLEKID SPOSGES
2-1I
that for width from 31.7 to 55.6. The mean lengths and widths of the 40-spicule
samples derived from 10 sponges each month also varied. I t seems likely in view
of these results that the coefficient of variation is characteristic for certain
species, but attention has to be paid to whether it is correlated with mean length
(respectively, mean width), whether it varies seasonally for a given species and
whether the seasonal variation is due to variation in mean length (width) or
differences in the standard deviation.
A property which does not appear to have been considered as a possible
diagnostic character for species discrimination is the degree of correlation
between spicule length and width. Rutzler (1981) plotted mean widths against
mean lengths to facilitate the distinction of species of Ulosa, but one could go
further. For a single growing spicule the relationship between width and length
could well be linear, at least over much of the growing period. The hydrated
silica, or spicopal, is laid down by a process of accretion that appears to be
periodic (see reviews by Jones, 1979 and Hartman, 1981), resulting in the
formation of a concentric lamination. The lamellae extend all round the spicule,
with the exception of the extreme tips, through which the fine organic axial
filament protrudes, at least in so-called ‘open’ spicules (Minchin, 1909).
Growth in both width and length therefore involves the same increase in
number of lamellae in the same time, and, even though the lamellar thickness at
the ends of the spicule, measured in the direction of the longitudinal axis, may
not be the same as the thickness measured transversely in the middle of the
spicule, nevertheless, the proportional relationship between them would be
expected to be constant. The resulting linear correlation between width and
length would only apply to the spicopal; prior to the secretion of hydrated silica
th’e organic axial filament is laid down as a slender rodlet in the vacuole
contained in the cytoplasm of the sclerocyte and the accretion of the spicopal
on.ly occurs when this has reached a certain length (approximately 40 pm in the
freshwater sponge Ephydatia jluuiutilis (Weissenfels & Landschoff, 1977)). Thus,
because only the spicopal survives boiling with fuming nitric acid (the treatment
used in the isolation of the spicules), the minimum widths and lengths in spicule
samples will not approximate to zero. For the same reason one can neglect the
observation of Weissenfels & Landschoff (1977) that the growth of the oxea of
Ephydutia Juviatilis takes place by alternating increases in length and width,
because the former concern only the organic axial filament; spicopal secretion is
periodic, as stated above. A linear correlation between length and the width of
the spicopal is to be expected.
Spicule lengths and widths vary widely within a single species and from one
species to another. Presumably variation arises from differences in the rate of
growth in length of the axial filament and the timing when spicopal secretion
commences. The shape of the vacuole may also affect the relative thicknesses of
lamellae at the middle and ends of the spicule; much would depend on whether
the spicule were sharply or bluntly pointed at either end. Within a given
specimen there may be variations between sclerocytes, some producing longer,
narrower spicules and others shorter, stouter ones. The abundance of
mitochondria per sclerocyte may vary or the ease of access of nutrients, so that
spicopal secretion relative to the secretion of organic substance for the filament
may vary. Thus the overall correlation between length and width for all of the
spicules in a sponge could well be slight. Jorgensen (1944) found relatively little
correlation between the widths and lengths of microscleres of juvenile Spongilla
242
W. CLIFFORD JONES
lacustris, but these tend to have variable curvature. I t is still necessary to
examine the megascleres of other species for possible close correlation and
where, if at all, the correlation be good, the constants of the regression line of
width on length may afford additional parameters to help in the
characterization and diagnosis of species.
In this paper ‘length’ is defined as the shortest distance between the two ends
of the spicule and ‘width’ as the cross-sectional thickness of the middle. Length is
taken as the independent variable, being the more accurately measured because
width measurements involve the use of an imaginary transverse line. Some error
will be involved in measuring the chord length rather than the true (arc) length
of the curved oxea, but the former is more useful for comparative purposes, endto-end measurements having traditionally been always quoted.
The principal diagnostic features besides spicule size that have been used in
this paper to identify species are as follows:
Adocia simulans (Johnston)-stone hard, regular skeleton, dermal reticulation;
A. densa (Bwk) (?)-dermal
reticulation, dense skeleton, numerous
intercrossing multispicular bundles, small spicules;
Chalinula limbata (Montagu)-multispicular spongin bundles, no gemmules;
Haliclona elegans (Bwk)-slime strands interconnect living fragments as they
are pulled apart;
H . oculata (Pallas)-branching habit, flexible, much spongin at base;
Reniera indistincta (Bwk)-soft to touch, multispicular bundles;
R. uiscosa (Topsent)-mucus
production, multispicular bundles, spicules
longer than in R. indistincta;
R . rosea (Bwk)-rose or orange colour, trispicular bundles;
R . jistulosa (Bwk)-hollow fistulae, closed at distal end;
R . macandrewii (Bwk)-long spicules, oscula on mounds;
R. obscura (Bwk) (?)-dense skeleton, multispicular bundles;
Gellius angulatus (Bwk)-presence of toxa and/or sigmata.
Other specimens have not yet been identified. Some of my specimens of R.
indistincta match the description of H. canaliculata Hartman (1958), which occurs
on the western side of the Atlantic. It remains to be seen whether these should
better be regarded as a first record for the American species in British waters (in
which case indistincta does not occur littorally in the vicinity of Bangor), or
whether canaliculata would not better be regarded as an American variety of
indistincta. With regard to A. densa(?), the two specimens studied could possibly
be a senile or condensed version of R. indistincta, the spicules being similar. Some
other specimens with dermal reticulation and a choanosome crowded with
intercrossing multispicular bundles likewise could be regarded as condensed
versions of rosea, or some other species. Relatively little is known about the
growth forms of the species in question.
MATERIALS AND METHODS
Specimens were collected during periods of low water Spring tides, mainly
from the shores of Rhosneigr (O.S. sheet 114; 311726: latitude 53’13”) and
Church Island (O.S. sheet 114; 551717: latitude 53”13.5’N), but a few littoral
S€'ICl.~LE DIMENSIONS IN HAPLOSCLERID SPONGES
243
<andsub-aqua specimens from other neighbouring sites were also included. The
llittoral sponges were fixed in 90% alcohol immediately after excising them from
Itheir substrate. Some were photographed in colour before removal, also many in
black and white on return to the laboratory. Surface slices and thin handsections perpendicular to the surface were then cut, dehydrated, cleared and
mounted in balsam to reveal the spicule arrangement. Special structures (e.g.
fistulae, oscular edge) were also excised and mounted. Spicule preparations were
ithen made by boiling representative parts of the sponge in fuming nitric acid,
washing by decantation and finally pipetting a suitably diluted suspension of the
spicules on to a microscope slide. After drying, a permanent preparation was
made by adding balsam and a coverslip.
Spicules were measured by projecting their images upon a horizontal frosted
glass plate (37 x 29 cm). A ruler was used to measure the spicules of the first 63
specimens, each being magnified 320 times ( x 25 objective). Measurements
were made on the enlarged images to an accuracy of 0.5 mm for length and
0.25 mm for width. Subsequently the measurements for a further 63 sponges
were made using a digitizer connected to a PDPl 1 computer. Before each set of
LOO spicule measurements was begun a stage micrometer scale was projected at
the same magnification and points at each end of 100 pm interval were recorded
for the purpose of calibration. Measurements were made at a magnification of
L 180 times, a 100 pm long spicule appearing as an 11.8 cm long image. T h e
resolution of the digitizer was 0.2 mm over the whole glass plate and this was
regularly checked. T h e lengths and widths in micrometres were automatically
stored in two columns on floppy disc by the P D P l l computer and later
transmitted t o a DEC 10 mainframe computer for analysis and graphical display.
RESULTS
Number of spicules measured per specimen
Preliminary trials indicated that similar results were obtainable from different
areas of a spicule preparation when even 50-spicule samples were compared, but
for greater confidence it was decided to measure 100 spicules. The spicules were
measured in order along a transect usually taken across the middle of the
coverslip, or in two subsamples of 50 spicules each from different areas of the
slide. Spicules that were out of focus or abnormally shaped, including the styli
and strongyli, were ignored. Table 1 gives data for four samples of a specimen of
H. elegans and two samples from the same preparation of a specimen of G.
angulatus. Three of the H. elegans samples (1-3) were derived from, respectively, a
large osculum, an area with a small osculum and an area without an osculum.
The fourth (4) concerned a spicule preparation made previously using an
unspecified part of the same sponge. The data for the combined 400-spicule
sample (5) are also given. Measurements were made using the ruler method.
The differences between the frequency distributions were not significant at even
the 15"L level using the Kolmogorov-Smirnov two-sample test except when
comparison of the width distribution between 2 and 3 (P=0.016) and between 3
and 4 (P=O.Ol) was made. The means, however, are sufficiently close. Only the
sample 4 length distribution approximated to a normal distribution
W. CLIFFORD JONES
244
Table 1. Columns 1-4. Statistical results concerning samples from different
parts of a specimen of Haliclona elegans. Column 5 concerns the combined data
from the four samples. Columns A and B give the corresponding results for two
samples of a specimen of Gellius angulatus. I n all cases the length and width
measurements are in microns. Measurement was by the ruler method for ff.
elegans and by the digitizer method for G. angulatus
1
Number of
observations
Mean length
Standard
deviation ( L )
Mean width
Standard
deviation ( W)
Median length
Median width
Mode for length
Mode for width
Maximum length
Maximum width
Minimum length
Minimum width
Coefficient of
variation ( L )
Coefficient of
variation ( W)
Correlation
coefficient
Regression
coefficient
Regression
constant
100
101.125
2
I00
101.27
H. eleganJ
3'
4
5
101.28
100
102.72
400
101.60
8.66
6.22
100
G. angulatus
A
B
100
100
193.72
192.68
23.01
6.68
23.04
6.45
1.37
196.29
6.955
115.12*
4.86;
242.06
10.25
115.12
2.41
1.24
196.18
6.705
89.81*
6.97
231.69
8.81
89.8 1
3.23
8.15
6.3
8.94
5.95
10.32
6.47
6.91
6.15
1.33
103.125
6.25
100.00
6.25
115.625
9.375
62.5
3.125
1.55
100.00
6.25
93.75*
6.25
118.75
8.59
65.625
1.56
1.49
103. I25
6.25
106.25
6.25
115.625
8.59
65.625
2.34
1.3
103.125
6.25
106.25
4.69*
115.625
9.375
87.5
3.91
8.06
8.83
10.19
6.73
8.53
11.9
12.0
21.08
26.07
23.10
21.11
22.98
20.5
19.2
1.43
103.12
6.25
106.25
6.25
118.75
9.38
62.5
1.56
0.7093
0.7245
0.7267
0.7159
0.7063
0.6349
0.5689
0.1 157
0.1256
0.1052
0.1345
0.1 165
0.0377
0.0305
- 4.1855
- 7.6683
-5.3954
-6.7713
-5.6198
-0.6241
f0.5624
*More than one mode exist; only the first is given.
(Kolmogorov-Smirnov test: P = 0.35). Compared with the combined sample the
four 100-spicule samples are reasonably representative. One can conclude that
spicule size is not influenced by the region from which the sample is taken in
H . elegans, a conclusion that probably has general application to the British
haplosclerids.
The two samples of a specimen of G. angulatus in Table 1 are added because
their spicules are much longer than those of H . elegans and they were measured
using the digitizer. The specimen was taken at random from the 28 specimens of
G. angulatus collected. Both the length and width distributions of both samples
approximate to normal distributions (P=0.26). Differences between the means
were insignificant (Student's t-test: P=0.75 for length and 0.21 for width) as
were those between the distributions (Kolmogorov-Smirnov: P = 0.99 for
length, 0.21 for width). Thus, taking samples of 100 spicules affords a
reasonably representative sample of the spicule populations. However, in
Table 1 it can be seen that the maximum and minimum values are not
necessarily included in such samples, but the discrepancies from the true
maxima and minima are not important. Hartman (1958) used 50-spicule
SPI(XLE DIMENSIONS IN HAPLOSCLERID SPONGES
245
samples in his studies of H. oculata and 100-spicule samples for H. loosanofi and
W.canaliculata.
Maxima, means, medians, modes and minima of the frequency distributions
In Fig. 1 the maximum, median, mean and minimum values of width for the
126 sponge specimens, comprising at least 12 species, have been plotted against
the corresponding values for length. I n none of the four diagrams is there a clear
segregation of the points into clusters representing single species. Even in the
diagram for the maxima, in which there is the greatest spread, the species
clusters merge and overlap, often quite extensively. Only G. angulatus (all points
to the right of the 190 pm length line) stands out, but even so one specimen has
intruded into the territory of R. macandrewii. A . simulans (top right), H. elegans and
11. oculata (both top left) and C. limbata (bottom left) all intrude into the central
.
....
.
..
0
.
* .
8::
... c.:.
+--."
9..
E
:
:
.+
.. . . .i
*
.*
Minima
.*
L
50
100
I50
200
250
Length ( p m )
Figure 1. Width-length diagrams for the 126 specimens of haplosclerid sponges. Species in some
cases have been indicated by placing a label immediately above or below the point concerned on
the graph of maximum values: a . G. angulatus; d , A . densa; e, H . ele,yans; i, R. indistincla; f. R.Jistulosa;
1, C.limbata; m, R. macandreuii; 0,H . oculata; ob, R. obscura(?);r, R. rosea; s, A . simulans; v, R. uisrosa.
W. CLIFFORD JONES
246
Table 2. The frequency distributions of the standard
errors (pm) of mean lengths and mean widths for spicule
samples derived from 126 haplosclerid specimens
Standard error
of mean length
o.o+
to 0.5
0.5+ to 1.0
1.0+ to 1.5
1.5+ to 2.0
2.0+ to 2.5
2.5+ to 3.0
3.0+ to 3.5
Number of
specimens
Standard error
of mean width
Number of
specimens
4
o.o+ to 0.1
0.1+ to 0.2
0.2+ to 0.3
101
5
29
60
19
20
11
2
1
area occupied by several intermingled species. Clearly spicule dimensions by
themselves cannot reliably serve for the identification of the species. Simpson
(1968) came to a similar conclusion for species of the Poecilosclerida.
The plots of medians and means are much alike, although the median is
usually considered to be a better indicator of the mid-point of a distribution. I n
Table 1 it can be seen that the median width was the same for all four samples
of H . elegans, whereas the median length varied slightly more than the mean.
Again for G. angulatus there was little to choose between means and medians of
either length or width for least discrepancy. Again specific clusters d o not stand
out.
The standard errors of the means are relatively small thanks to the sample
size. As Table 2 indicates, in only five cases was the error in the 0.2-0.3 pm
range for width and in only 14 samples did it exceed 2.0pm for length. The
standard error is an estimate of the standard deviation of the population mean,
so that with such small errors the means of the spicule populations are
reasonably accurately displayed on Fig. 1. The largest standard errors for length
(2.0-3.5) all concerned G. angulatus, as did also 10 out of the 19 specimens in the
range 1.5-2.0. Thus the larger standard deviations concern the samples with the
longer spicules. I n the case of width three of the five largest standard errors were
attributable to H. oculata and one each to H . elegans and G. angulatw.
The frequency distributions were not infrequently polymodal. The positions
of the modes are usually of minor value, because much depends upon the size of
the class intervals. However, they can be useful in demonstrating the difference
in spicule width reached by spicules growing during the summer months, as will
be shown below. Some distributions approximated to normal distributions, but
commonly the distributions exhibited negative kurtosis and a ‘shoulder’ on the
left side of the mode, as would be expected from the presence of developing
spicules.
The diagram of the minimum values in Fig. 1 indicates a wide spectrum of
length minima. It seems clear that the organic filament can vary in the length at
which silicification begins. The minimum lengths for G. angulatus tended to be
greater than those for species with shorter spicules. The minimum value for
width that was measured throughout the 126 specimens was 0.51 pm ( R . rosea).
The thickness of the organic axial filament in species of Haliclona has been
directly measured as 0.2 and 0.34pm (Garrone, 1969; Garrone, Simpson &
Pottu-Bournandel, 1981; figs 17-8, 17-9).
SPICULE DIMENSIONS I N HAPLOSCLERID SPONGES
247
Correlation coejicients and regression lines
Table 3 shows the frequency distribution of the rounded-off correlation
coefficients ( r ) comparing lengths with widths for the 126 specimens. It can be
seen that whereas some values are close to 0, indicating poor correlation, by far
the majority lie above 0.5 and in 7 cases the value exceeds 0.8. Table 4 gives
details of these 7 examples and it is clear that neither the date when the sponge
was collected, nor the collecting site, are of particular significance in gaining
high r values. Some species showed a considerable range of values. Thus C.
limbata coefficients ranged from 0.2838 to 0.6410 (3 specimens), R. rosea from
0.2704 to 0.8531 (27 specimens) and G . angulatus from 0.2838 to 0.8835. Such
wide ranges indicate that the correlation coefficient is unlikely to be of use in the
identification of species. They stem, in fact, from the variability in numbers of
juvenile spicules in the samples; when there are few small spicules the scatter
diagram of width on length appears as a cloud, whereas when there are many a
broad, approximately linear, band is obtained, sloping up from left to right. I n
the former case the regression lines of width on length and length on width are
widely divergent, whereas in the latter they become more-or-less coincident, with
Table 3. Frequency distribution of the coefficients of
correlation between length
and width in spicule samples derived from 126 haplosclerid specimens
Number of
specimens
r
O.O+ to 0.1
0.1
to 0.2
0.2+ to 0.3
0 . 3 f to 0.4
0.4+ to 0.5
0 . 5 f to 0.6
0.6+ to 0.7
0.7+ to 0.8
0.8+ to 0.9
+
2
2
6
5
9
26
39
30
7
Table 4. Samples with width-length correlation
coefficients exceeding 0.8 listed by species, date of
collection and site of collection
5pcc 1 ' 3
r
Date of
collection
0 8835
0.8277
0 8591
0 8031
0 8367
0 8531
0 8182
19 Mar 1981
19 Mar 1981
19 M a r 1981
16 May 1980
16 May 1980
30 Jul 1980
27 Aug 1980
Site
~~
(7
K
K
R
H
R
angulatu
rosea
obscura
rosea
elegans
rosea
H elegans
Church Island
Church Island
Church Island
Rhosneigr
Rhosneigr
Church Island
Rhosneigr
250
0
Width I p m )
d
0
0
I
I
I
I
50
100
Length ( p m )
I50
200
Figure 3. Graphs of the regression lines of the coefficient of variation for width (above) and length
(below) plotted against the mean values for width and length respectively. Also included are the
average coefficients for certain species together with their standard deviations. Labelling as in
Fig. 1 .
The average coefficient of variation for both length and width for each
species, and the standard deviations of the distributions are shown graphically in
Fig. 3 . Also included are the regression lines of the coefficients against mean
values, for which the equations have already been given. It can be seen that
while some species straddle the regression lines, others stand apart. Thus
C. limbata and H. oculata have high coefficients for length, whereas A. simulans and
A . densa (?) have low coefficients. It is interesting that both C. limbata and
H. oculata have relatively large amounts of spongin, while A. simulans has a regular
skeletal reticulation and the specimens of A . &ma(?) were peculiar in having few
juvenile spicules. However, further research would be needed before satisfactory
explanations of these differences could be given. For width H. oculata,
A. densa(?) and R. indistincta likewise stand apart. These apparently speciesdependent differences, together with the usually great variation in coefficients
shown by each species, explain why the correlations between the coefficients and
the mean values were so poor.
SPICXJLE DIMENSIONS IN HAPLOSCLERID SPONGE5
25 1
To some extent the variation in the coefficients can be related to the date on
which the sponges were collected. Because most of the specimens were collected
littorally on low spring tides, the times of collection fell on the same day (to
within a day or so) in the same month each year, so that average values could
be calculated for short periods each month. When all of the data, irrespective of
species, were lumped together it was found that the mean coefficient of variation
for width decreased significantly (P<0.05) in May and rose again in June.
However, this result could be an artifact, caused by the collection of an
,abnormally large number of specimens of a species characterized by a low
coefficient of variation in May. I t would be better to compare the coefficients
month by month for a single species. This has been done for G. angulatus and
H. elegans, for both of which there was an adequate number of specimens collected
throughout the spring and summer months. The graphs are given in Figs 4 and 5.
[n both cases the average coefficient for width drops strikingly in May,
confirming the drop obtained when all specimens were lumped together. The
mean coefficients for R. rosea are significantly different between May and July
i(P<O.OOI), May and beginning of August (P<0.005) and May and the end of
August (P<0.05). Between April and May, and April and July, the difference
is only significant at the 10% level. For G. angulatus the differences are not
significant at the 5% level, but nearly so between March and May (P<0.06)
and between April and May (P<0.07). The average coefficients for length for
R. rosea also vary somewhat with the date of collection, the differences being
significant between March and May (P<0.05), March and July (P<O.OI),
March and the beginning of August (P<0.025) and May and the start of
...-
I
Mar
Apr.
I
I
May
Jun
I
Jul
pug
Figure 4. Graph showing the variation in the average coefficient of variation for width (circles; and
length (spots' with the date of collection irrespective of year for R. romz. The standard deviations of
thc averages arc also shown.
W. CLIFFORD JONES
252
T
30
0
c
._
._ 2 0 0
L
c
acl
.-
0
._
c
a,
s
l0-
0
Mar.
Apr.
May
Jun.
Jul.
Aug.
Figure 5. Graph showing the variation in the average coefficient of variation for width (circles) and
length (spots) with the date of collection irrespective of year for G. angulatus. T h e standard
deviations are also shown.
August (P<0.05). For G. angulatus, the differences are only significant at the
10% level between April and July, and May and June. All of the specimens of G .
angulatus were collected a t Church Island, whereas the R. rosea specimens were
taken from both Church Island and Rhosneigr. However, when only the
Church Island specimens of R. rosea were considered, the graphs for the
coefficients against date of collection varied in the same manner as for the
combined R. rosea data.
The explanation for the changes in coefficients of variation with date of
collection does not lie solely with corresponding variations in mean length and
width, the monthly averages for which are graphically displayed in Figs 6 and 7.
Significant differences in average mean width for R. rosea (combined data) only
occur between May and July (P<0.025), and in average mean length between
100
Mar
Apr.
May.
Jun
Jul.
Aug.
Figure 6. Graphs of mean widths (above) and mean lengths (below) together with the standard
deviations, plotted against the date of collection irrespective of year for R. 7oseu. T h e numbers of
specimens from March to August were, respectively, 6, 4, 13, 5, 3 and 2.
S P l C I LE DIMENSIONS IN HAPLOSCLERID SPONGES
I
. -.,I
--...
Mar
Apr
May
2.53
Jun
Jul
Aug
Figurc 7. Graphs of mean widths (abobe) and mean lengths (below) together with the standard
deviations, plotted against the date of collection irrespective of year for G. angulalus. T h e numbers of
spccimens from March to .4ugust were, respectively, 6 , 6 , 3, 6, 3 and 4.
April and the start of August (P<0.025), and July and the start of August
(P<0.005). The slight rise apparent in average mean width in May (from 5 to
5.26 pm) would reduce the average coefficient to 27.35 were the standard
deviation of the April specimens to remain constant, whereas the actual
coefficient for May is 24.7. Moreover, the graphs of variation in average mean
width and length are not the inverse of those for the average coefficient. For G.
a,ngulatus, the average mean fell slightly in May, so that the coefficient for width
should have increased. However, the differences in average widths were only
significant at the 5% level between May and June. There were no significant
differences in average mean length. Again comparison of the graphs for the
average coefficients and average mean widths or lengths suggests that variations
in the latter are not solely responsible for variations in the former.
It seems that changes in standard deviation occur throughout the spring and
summer months at least. The average standard deviation for width in R. rosea
dropped from 1.44 to 1.29 between April and May and then rose to 1.72 in July.
For length, the corresponding changes in average standard deviation were from
11.59 in April to 11.32 in May to 12.77 in July. For G. angulatus, the average
standard deviation for width dropped from 1.37 to 1.01 from April to May and
rose to 1.345 in June; for length the corresponding changes in standard
deviation were 19.40 to 15.82 to 21.585. Changes in the standard deviation
could have arisen from either a cessation or increase of growth, so that samples
were deficient or rich in juvenile spicules. Alternatively there could have been a
change in the size of the fully grown spicules, associated with the decline in
concentration of silica in the seawater or the rise in temperature during the
period April to September (Hartman, 1958; Stone, 1970a; Simpson, 1978). To
investigate these possibilities, the frequency distributions and microscope
sections of the sponges will now be considered in more detail.
Frequency distributions
Figures 8- 1 1 show the frequency distributions for widths and lengths for
R. rosea and G. angulatus. Data from all of the specimens collected per month have
W. CLIFFORD JONES
254
0
5
10
5
0
Width (pm)
Figure 8. Combined frequency distributions for width for R. Tost-a. The numbers of specimens from
March to August are given in Fig. 6.
been lumped together. The combined distribution for width for R. rosea is the
most interesting, because it can be seen that progressively from March to the
end of August there is an increase in the number of spicules in the class 3 to
4 pm. When the sponge sections of R. rosea were examined it was obvious that
during the spring slender spicules were present in often great numbers in the
meshes of the skeletal framework (Bowerbank presumably would have termed
these 'tension spicula'), whereas similar spicules were incorporated distally in
the primary bundles in specimens collected in July and August. Spicules are
transported to their ultimate site in freshwater sponges only after completion of
growth and liberation from the parent sclerocyte (Weissenfels, 1978), so that it is
2ot-J=-l
k
-"I
19Mar.
2 Jun.
0
b
a
0
l-AdlJk
I Aug.
00
5
10
0
5
10
Width
Figure 9. Combined frequency distributions for width for G. angulatus. The numbers of specimens
from March to August are given in Fig. 7.
SPICULE DIMENSIONS IN HAPLOSCLERII) SPONGES
255
1
2 Jul.
40
t
128Aug
l 5 May
",
0
50
100
150
50
I00
I50
Length ( p m )
Figure 10. Combined frquency distributions for length for R. rosea. T h e numbers of specimens are
the same as in Fig. 6.
reasonable to suppose that the slender spicules in the bundles were fully formed.
Also some specimens showed extensive regions in which only thin spicules were
evident, and it seems likely that not all of these would be juveniles in view of the
one or two days only that are required for complete spicule growth. For G.
angulutus (Fig. 9), the effect is not obvious, but specimens in July and August
also exhibited slender spicules distally in the primary bundles. The effect is
perhaps masked in Fig. 9 by having lumped the data from different specimens
together; for considerable differences in the maximum lengths and widths were
evident between the specimens. It would be better to make samples from the
same specimen throughout the year in order to follow the changes in spicule
frequency distributions. However, the almost total absence of spicules of less
than 3 pm width in May in both Figs8 and 9 does suggest that the fall in
standard deviation in this month resulted mainly from a cessation of spicule
production in both species.
The distributions for length for both species are given (Figs 10, 1 1 ) and they
confirm that juvenile spicules were scarce round about April-May. However, it
would be unwise to draw any other conclusions from them, because they
represent the combined data for a number of specimens. Stone (1970a) found
that the length declined with decreasing silica concentration in the seawater,
and comparing the distributions for July and August for R. roseu (Fig. l o ) , there
does appear to be a decrease in the percentage in the range 140-170 pm. For G.
angulutus the interpretation is difficult probably for reasons already given.
DISCUSSION
It has been shown that spicule dimensions by themselves are insufficient for
identifying species in every case, but that some specimens can be so identified
when their spicule mean and maximum sizes fall within a cluster that only
partially overlaps the clusters for other species. Spicule shapes and arrangements
W. CLIFFORD JONES
256
I
19 Mar
40- 2 3 A p r
20 0
40- 15 May
40
.
0
2 050
IAug.
100
Length
I50 ( p m )
200
25C
Figure 1 I . Combined frequency distributions for length for G.angulatus. The numbers of specimens
are the same as in Fig. 7.
have not yet been considered and are outside the scope of this paper. The
statistical analysis of the spicule dimensions, however, has yielded parameters
which may be of help to the taxonomist. The linear regression constants when
the correlation between spicule width and length is good are characteristic of
the species to some extent, and may help in deciding how closely related are
certain species. The differences between the slopes of certain regression lines
require explanation. The correlation coefficient ( r ) by itself is of little use,
because it varies widely within species, depending upon whether there is an
adequate number of juvenile spicules in the sample and specimen.
The coefficient of variation could well be of taxonomic value, although its
usefulness is marred by the variation shown between specimens collected at
different times during the spring and summer. I t has been shown that some
species conform to the general rules that, on the one hand, the coefficient for
width tends to decrease with increasing mean width, whereas, on the other, the
coefficient for length tends to increase with increasing mean length, but other
SPIC[ .LE DI.MENSIONS I N HAPLOSCLERID SPOS(;ES
257
:species stand out in these respects. Further research is needed to explain why the
coefficient of variation for width should decrease so markedly in May. For
.Hymeniacidon perleve Stone (1970aj found that the coefficient of variation for both
width and length was greater during the months of May, June and July than for
the remaining months of the year. Thus the length coefficient for June was 28.4
in contrast to 17.6 in October. The mean lengths correspondingly were 239 and
294 pm. For width the maximum and minimum values were 55.6 (June) and
3 1.7 (September), respectively, and the corresponding means were 4.26 and
5.26. Thus the length coefficient decreased as mean length increased in contrast
1.0 the trend reported above for haliclonid species. The megascleres of
AYymeniucidon are monactinal styli and subtylostyli in contrast to the diactinal
oxea of the haplosclerids. The species are not closely related. There is thus no
reason to believe that the respective coefficients of variation should vary in the
siame way.
The tendency for thinner spicules to be formed during the spring and summer
months has been confirmed, particularly for R. rosea, but a satisfactory
cxplanation cannot as yet be given. Experimental research would be required in
order to determine the various factors. The local variations of temperature and
silica concentration in the seawater should be taken into account, together with
the periods of growth of the sponge concerned. Also seasonal samples from the
same specimens should be compared. It is interesting that Stone (1970a)
discovered in Hymeniacidon perleve that the mean length and width increased from
June to October, while the silica concentration increased from July to October
and the sponge grew from June to September (Stone, 1970b). Clearly the
obvious presence of juvenile spicules during the growing period did not diminish
the mean lengths and widths recorded and the increase in the means actually
obtained does suggest an effect of the increasing silica concentration. It is
nevertheless puzzling that juvenile spicules should have formed in abundance
during April and May when the concentration of silica was minimal and the
sponges werc in a state of regression (Stone, 1970b). They must have been
forming then for an effect of the silica concentration to have been noticeable;
minimal spicule mean size coincided with a trough in silica concentration. If the
slender spicules had been derived from normally sized spicules formed earlier,
there would have been evidence of spicule corrosion. Clearly, care must be taken
to discriminate between -juvenile spicules and slender, fully-grown spicules when
correlating spicule mean dimensions with variations in environmental
conditions.
The tendency for thin spicules to be incorporated distally in the primary
bundles to some extent contradicts the conclusion drawn above for H . elegans
that spicule mean size is independent of site in the sponge. Preferably, spicule
samples should not be taken from a thin surface sl!ce of the specimens. The
development of thin spicules is a further source of confusion for the inexpert
sponge taxonomist.
ACKNOWLEDGEMENTS
The digitizer was designed and constructed by M r D. A. Davies of the
School of Animal Biology, Bangor, and it is a pleasure to acknowledge his help
and advice in connection with the operation of this facility. Measurements made
258
W. CLIFFORD JONES
by the ruler method were undertaken by Mr G. M. Jackson as part of a student
project. Mr S. C. Jones and Miss Sarah E. Jones have also given technical
assistance in spicule measurement and in computation. To all these and to the
staff of the Computing Laboratory, U.C.N.W., Bangor, in particular Mr I. G.
Jones, I should like to express my sincere thanks.
REFERENCES
ARNDT, W., 1935, Die Tierwelt der Nord- und Ostsee. IIIa. Porifra: 1-140. Leipzig: Grimpe & Wagler.
BERGQUIST, P. R. & WARNE, K. P., 1980. The marine Fauna of New zealand: Porifera. Demospongiae. Pt 3
(Haplosclerida and Nepheliospongida). New Zealand Oceanographic Institute Memoir, 87: 1-42.
BOROJEVIC, R., CABIOCH, L. & LEVI, C., 1968. Inventaire de la F a m e marine de Roscoff. Spongiaires. Paris:
Robin & Merenge.
BOWERBANK, J. S., 1866, 1874, 1882. A Monograph of the British Spongiadae, 2: 1-388; 3: 1-367; 4: 1-250,
Ray Society. London: Hardwicke.
BURTON, M., 1926a. The relation between spongin and spicule in the Haploscleridae. Annals and Magazine of
Natural History. Series 9, 17: 265-267.
BURTON, M., 1926b. Observations on some British species of sponges belonging to the genus Reniera. Annals
and Magazine of Natural History, Series, 9, 17: 415-424.
BURTON, M., 1947. Notes on the sponge Haliclona indistincta (Bowerbank). Annuls and Magazine of Natural
Histoy. Series 11, 14: 369-372.
BURTON, M., 1948. The synonymies of Haliclona angulata (Bowerbank) and H. arcoferus Vosmaer. Annals and
M a g e i n e of .Natural History. Series 12, I : 273-284.
FRY, W. G., 1970. The sponge as a population: a biometric approach. I n The Biology of the Porifera. Symposia of
the zoological Society of London, 25: 135-162. London: Academic Press.
GARRONE, R., 1969. Collag.?ne, spongine et squelette miniral chez 1'Cponge Haliclona rosea (O.S.)
(DCmosponge, Haploscleride). Journal de Microscopie, 8: 58 1-598.
GARRONE, R., SIMPSON, T . L. & POTTU-BOUMENDIL, J., 1981. I n T. L. Simpson & B. E. Volcani
(Eds), Silicon and Siliceous Structures in Biological Systems: 495-525. New York: Springer-Verlag.
GRIESSINGER, J.-M., I97 1. Etude des RCnitrides de MCditerranCe (DCmosponges Haplosclerides). Bulletin
du Musium Nationale &Histoire Naturelle, Siries 3, zoologic: 97-1 75.
HARTMAN, W. D., 1958. Natural history of the marine sponges of Southern New England. Peabody Museum
of ~VaturalHistory, Yale Uniuersity, Bulletin 12: 1-155. New Haven, Connecticut.
HARTMAN, W. D., 1981. Form and distribution of silica in sponges. In T. L. Simpson & B. E. Volcani
(Eds), Silicon and Siliceous Structures in Biological Systems: 453493. New York: Springer-Verlag.
JONES, W. C., 1979. The microstructure and genesis of sponge biominerals. In Biologie des Spongiaires.
Colloques Internationaux de Centre National de la Recherche ScientiJique, 425447. Paris.
JORGENSEN, C. B., 1944. O n the spicule formation of Spongilla lacustris. I . The dependence of the spiculeformation on the content of dissolved and solid silicic acid of the milieu. Det Kongelige Danske Videnskabernes
Selskabs. Biologiske Meddel, 19(7): 1 4 5 .
MINCHIN, E. A,, 1909. Sponge-spicules. A summary of present knowledge. Ergebnisse und Fortschritte der
<oologie, 2: I 7 1-274.
RUSSELL, F. S., 1957. (Ed.) Pbmouth marine Fauna. 3rd edn Plymouth: Latimer, Trend & Co.
RUTZLER, K., 1981. An unusual bluegreen alga symbiotic with two new species of Ulosa (Porifera:
Hymeniacidonidae) from Carrie Bow Cay, Belize. Marine Ecology, 2: 35-50.
SIMPSON, T. L., 1968. The structure and function of sponge cells: new criteria for the taxonomy of
poecilosclerid sponges (Demospongiae). Peabo4 Museum of Natural History. Yale Uniuersily. Bulletin 25:
1-141. New Haven, Connecticut.
SIMPSON, T. L., 1978. The biology of the marine sponge Microcionaprolifera (Ellis & Sollander). 111. Spicule
secretion and the effect of temperature on spicule size. journal ofExperimenta1 Marine Biology and Ecology, 35:
3142.
STEPHENS, J., 1912. Clare Island survey. Pt 59. Marine Fauna. Proceedings of the R ~ y a lIrish Academy, 31:
1 4 2 . London: Williams & Norgate.
STEPHENS, J., 1916. Preliminary notes of some Irish sponges. The Monaxonellida (Suborder
Sigmatomonaxonellida) obtained by the Fisheries Branch of the Department of Agriculture and Technical
Instruction, Ireland. Annals and Magazine of ,Vaturul Hzstory, Series 8, 20: 232-242.
STONE. A. R., 1970a. Seasonal variations of spicule size in Hymeniaczdon perleae. Journal of the marine Biological
Association, U.K., 50: 343-348.
STONE, A. R., 1970b. Growth and reproduction of Hymeniacidon perleue (Montagu) (Porifera) in Langstone
Harbour, Hampshire. Journal ofzoology, London, 161: 443459.
TOPSENT, E., 1887. Contribution a I'ttude des Clionides. Archiues de Z-oologie exp4rimentale el g h i r a l e , Sine, 2, 5,
Mimotre 4 ( S u p p l h e n t ) : 1-165.
SPIC1JI.E DIMENSIONS I N HAPLOSCLEKID SPONGES
2.59
‘L‘OPSENT, E., 1891. Essai sur la faunr des Spongiaires de Roscoff. Archiues de zoologie exphimentalr et @zCrale,
.Sdrie 2, 9: 523-554
VAN SOEST, R. LV, .M. & WEINBERG, S., 1980. A note on the sponges and ortocorals from Sherkin Island
.and lough Ine, County Cork. The Irish hhturalists’ Journal, 20: 1-15.
WEISSENFELS, N. & LANDSCHOFF, H.-W., 1977. Bau und Funktion des Susswassersrhwarnms Epphydatia
,fluuiatili\ L. Porifrral. IV. Dic Entwirklung der monaxialen SO,-Nadrln in Sandwirh-Kulturen.
.<oologtsche Jahrbucher. Ableilung Anatomie und Ontqgenie der ‘Tiere, 98: 355-37 1 .
WEISSENFELS, N.,1978. Bau und Funktion des Susswasserschwamms Ephydatza Juzzatzlis L. (I’orifera , , \..
Das Nadclskrlrt iirid seinr Entstchung. Zoologische Jahrbucher. Abteilung Anatomie und Ontqenze der 7 i e r e , 99:
:?I 1 223.