James Scott Bowerbank.

A monograph of the British Spongiadæ online

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and fully developed, while the proximal one is, compara-
tively, produced to a very limited extent, as in Pigs. 137
and 138, Plate VI, each of these is subject to a certain
extent, to similar degrees of further diversity of form,
which may be designated bidentate, tridentate and
palmate. These forms are in truth but different degrees of
development of the normal palmate form ; but as we find
these variations constant in different species of sponges, it
is desirable that they should be separately designated,
as they afford excellent specific characters. Thus in
Halichondria ffranulata, Bowerbank, we find large equi-
anchorate spicula, in which the lateral expansions of each
end of the curved shaft or bow which forms the palmate
terminations of the spiculum extend along the shaft towards
the middle of the bow, very little beyond the point of
curvature forming the basal commencements of the hooks ;
but although not decurrent on the shaft, the hues of the
inner margins are projected forward at an angle of about
45 degrees to the axis of the shaft ; and as the outer lines
are projected in a corresponding degree, we have the palm
produced in the form of two concave conical teeth or palms
at each end of the spiculum ; and between these there is
not the slightest appearance of the ends of the hami, which
appear to be equally divided between the terminal palms or
teeth. This form I therefore term bidentate equi-anchorate.
The same termination occurs among the inequi-anchorate
forms; and this mode of the development of the teeth
is well shown in the distal or larger portion of the bidentate
inequi-anchorate spiculum, represented in Fig, 137, Plate
VI. In other cases the termination of each hook does not
thus merge in the teeth, but is carried forward between



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OP THE SPONGIADiB. 47

them either in the form of a simple attenuated termination,
as represented in Fig. 140, Plate VI, or it expands laterally
and forms a third intermediate tooth of a hastate form,
as represented in Fig. 147, Plate VL In either of these
cases I therefore designate the spiculum as tridentate. In
other cases, the lateral expansions forming the palm are
continued along the shaft of the spiculum to nearly, or
quite, the full extent of the palm, forming a single,
undivided, more or less concave termination, as in Fig. 138,
Plate VI. I propose, therefore, to designate this form as
palmato-anchorate ; and intermediate forms between the
decidedly dentate or palmate ones would be designated as
tridentato-palmate (Fig. 138, Plate VI), the palmate form
being in excess of the dentate structure ; or palmato-tri or
bi-dentate, when the teeth are in the ascendant.

Generally speaking, the ends of the shaft of each
anchorate spiculum either become obsolete at the base of
the teeth, as in bidentate forms, or they are continued in a
regular curve, forming the third tooth, as in the tridentate
form ; but in some cases, as in Halichondria plumosa^
Johnston, the shaft appears to terminate abruptly at each
end, and the palms or teeth are projected towards each
other at a sharp angle to the ends of the shaft or bow
of the spiculum : in this case we should term the spiculum
angulated anchorate, as represented in Figs. 141, 142 and
143, Plate VI.

The anchorate spicula are not, like the acerate, acuate
and other simple forms, of the same shape, or nearly so,
from the commencement to the termination of their
growth, but, on the contrary, they are developed pro-
gressively.

In a new species of Halichondria, for which I am
indebted to my late friend, Mr. Thomas Ingall, the
course of their development is displayed in a very interest-
ing and instructive manner. The fii:st condition in which
we detect them is in the form of an exceedingly slender
and elongated simple bihamate spiculum, which is readily
distinguished from the true bihamate form by the straight-
ness of the shaft, the comparative shortness of the hami, and



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48 ANATOMY AND PHT8I0L06T

the obtuseness of their terminations, as represented in
Rg. 144, Plate VI. We next find the same form increased
in strength, and with slight lateral fimbria near each end
of the shaft at the commencement of the hami, as in Fig.
145, Plate YL In a more advanced state we find a
regularly curved extension of the fimbriae, slightly so
at one extremity of the shaft, and considerably so at the
other; and as the development progresses, the curves
of the fimbriae are extended in an outward direction, and
become angular; the extremities of the hami expand
laterally and assume a foliated appearance, as seen in
the distal or larger end especially (Fig. 146, Plate VI),
but the fimbriae at the smallest or proximal end of the
spiculum, and the foUated extremity of the adjoining
hamus, are still sepiurated from each other; and this
progressive development may be observed in all its stages,
until the connexion of the parts is completed, and the fully
developed form represented in Fig. 147, Plate VI, is
produced. The same progressive development of this form
of spiculum may be traced in those oi Hymeniacidon lingua^
Bowerbank, fix)m the Hebrides.

In the performance of their natural office in the sponge,
we find the same laws of attachment and projection obtain
that I have described in treating of the bihamate spicula.
In the equi-anchorate forms, where the terminal palms
or teeth are equally developed, the shaft is attached by the
middle of the external curve ; but in the inequi-anchorate
forms, where one palm is developed to a very much greater
extent than the other, we find the smaller one is attached
to the membrane, and the larger is projected at about
an angle of 45 degrees. Generally speakmg, the ancho-
rate spicula, like the bihamate ones, are irregularly dis-
persed over the surface of the membranes, but occasionally,
as in Hymeniacidon lingua^ they are developed in circles or
rosette-formed groups.

In many cases these groups contain so large a number of
spicula as to render any attempt to count them ineflfectual,
and in some instances so many are developed that the
group assumes the form of a ball rather than that of a



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OF THE SPONGIADiB. 451

rosette. Fig. 297, Plate XVIII, represents a rosette-
shaped group containing about the usual number of
spicula.

Besides the rosette-shaped groups in Hymeniacidon linguay
there are a considerable number of these spicula dispersed
over the surfaces of the membranes, but the attachment of
these spicula is more frequently at the middle of the shaft
than at the smaller end of the spiculum, their normal point
of attachment. In the single and separate mode of dis-
position they are performing the office of equi-anchorate
spicula, and the mode of their attachment is varied accord-
ingly ; but under these conditions they are rarely ever so
fully developed, nor do they attain the same size as those
which form the radiating groups. Notwithstanding the
numerous groups and dispersed spicula of the inequi-
anchorate form, this sponge is also abundantly furnished
with bihamate spicula of various forms, but they are never
congregated like the anchorate ones.

The same radiating mode of arrangement occurs in
a parasitical Australian sponge from Freemantle, but the
form of the terminations of the spicula is very different
from those of Hynieniacidon lingua. The distal termination of
each of the inequi-anchorate spicula is shortened in length,
but expanded laterally to a considerable extent, and
its terminal edge is furnished with three thin pointed
teeth. The distal end has two small expanded and raised
wings, projected in the direction of the inner curve of the
spiculum, and so disposed as to cause it to resemble very
closely an engineer's spanner for bringing up to their
bearings projecting square-headed screws. Thus, although
the forms of the termination of the two varieties of spicula
vary to a considerable extent, the principles of their
structure and purposes are in perfect unison. Fig. 135,
Plate VI, represents a single spiculum highly magnified
to display the peculiarity of their structure.

As may be imagined, from their office and situation in a
thin stratum of a gelatinoid sarcode, they are at all times
«mall, and in many cases so minute as to require a micro-
scopic power of at least 600 linear to render their structure

4



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50 ANATOMY AND PHYSIOLOGY

distinctly visible. They occur in all parts of the sarcodons
surfaces of the interior of the sponge, and are frequently
found in greater profusion than usual on the inner or
sarcodous surface of the dermal membrane; but I do
not recollect an instance of iheir occurrence on the outer
surface of that organ^ while on the sarcodous or interstitial
membranes they are frequently to be observed in about
equal proportions on both sides of the same membrane.

It will not be necessary to describe or figure the whole
of these variable forms of spicula. I have therefore selected
those only that may be considered more especially as type
forms.

Spicula of the Sarcode.

As the tension spicula of the membranes are destined to
strengthen and support those tissues, so the numerous and
beautiful tribe of stellate spicula appear to be devoted to
connect and give substance, and in some instances to
defend the gelatinoid sarcode, which so abundantly covers
the whole of the interior membranous structures of the
sponges in which they occur. It is difficult at first sight
to determine the diflFerence in the office of this class of
spicula, and those of the internal retentive ones ; and it is
probable that in some cases, when it so happens that the
radii of the stellate forms rest on, and become cemented to
the membranous structures, they may perform, to a certain
extent, the same function, that of assisting to connect the
membranes and sarcodous structures more finnly together.
'But generally speaking this is not the case, and especially
with the smaller forms of these organs ; for in compara«
tively thick layers of sarcode we find them in all parts, and
manifestly unconnected with the membranes beneath;
and in sponges which have undergone such an amount
of decomposition as to leave the membranous structures
entirely, or very nearly, free fi-om sarcode, while we see
the retentive forms remaining firmly attached to the
membranes, we rarely find the stellate ones, excepting
when entangled among the surrounding spicula of the



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OP THE SPONGIADiE. 51

skeleton. We may, therefore, reasonably conclude, that
their normal function is that of increasing the strength and
substance of the sarcodous structure of the sponge.

In the performance of this office of strengthening and
supporting the sarcode, we find a singular class of spicula,
consisting of from three to six rays, emanating from a com-
mon centre, and always disposed at right angles to each
other. Between the extreme forms of development of these
and the simple stellate spicula, there is a very great amount
of structural difference ; but on a more intimate acquaint-
ance with the intermediate forms, we find them passing
into each other so gradually as finally to connect the whole
into one group.

It is not in the Spongiadae only that these singular and
beautiful organs are found. In the soft parts of the
extensive family of the Gorgoniadee they are in vast
abundance, and in every variety of form, from an elongate
tubercular spiculum to the elongo-stellate forms of the
Spongiadae, and the prevalence of the bluntly terminated
radii is strongly indicative of their non-defensive character.
But this latter quality does not obtain in other cases,
either as regards the higher tribes of animals or the Spon-
giadae. Thus we find in numerous species of compound
tunicated animals their fleshy substance is crowded with
sphero-granulate spicula, very closely resembling in form
those of the sphero and subsphero-stellate shapes so abun-
dant in Tethea Ingalli and T. robusta (Figs. 164 and 165,
Plate VI). In both these cases the acute termination and
the peculiarities of their respective situations are indicative
of their subserving the office of defensive, as well as that of
consolidating spicula.

Simple Stellate Spicula.

Stellate spicula are composed of few or many radii
emanating from a centre in all directions. Their simplest
form is when the bases of the radii all proceed from a
common central point (Fig. 158, Plate VI), in which case
they should be designated simply, stellate spicula; but



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52 ANATOMY AND PHYSIOLOGY

when the radii spring separately and distinctly from a
common central spherical or oval base, they should be
designated sphero-stellate spicula (Figs. 162, 164, 165,
166,167, Plate VI). In both these classes of spicula there
is a very considerable difference in their size and form, in
the various species of sponges in which they occur.

Compound Stellate Spicula.

The curious and beautiful forms of this series of spicula
all belong to the class of sponges that have a skeleton
composed of siliceous fibre, and they are principally from
tropical climates. The central basal structure from which
the radii are projected, in. every case with which I am
acquainted, is a rectangulated hexradiate spiculum, from
the apices of which a variety of beautiful terminations are
projected, which vary in form exceedingly in different
species of sponges. In the class of sponges to which I
have alluded there are also numerous rectangulated spicula,
varying in the number of radii from three to six, the
apices of the radii being either acutely terminated or more
or less elevated, and these forms vary very much in size.
They are unconnected with the skeleton, and evidently
belong to the Sarcodous system of the sponge. They are
very much larger than the hexradiate centres of the com-
pound stellate spicula, but as they are evidently the normal
forms of that tribe, I shall describe the general characters
of these large, simple, hexradiate forms before those of the
more complicated stellate ones.

Attenuated rectangulated hexradiate (Fig. 174, Plate
VII.) — The first state in which we find them is in
that of an inequi-acerate spiculum (Fig. 175), in which
condition they are in fact the two axial radii of the
hexradiate form which they ultimately attain when in
their fullest state of development. In the next stage we
find a bud-like projection issuing from the side of the
thickest portion of the inequi-acerate spiculum (Fig. 176),
which is ultimately developed in the form of a rectan-
gulated triradiate spiculum, as in Fig. 179. Or two buds



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OF THE SPONGIAD^. 53

are simultaneously projected, as in Figs. 177 and 178, and
the result is a regular rectangulated quadriradiate form, as
in Fig. 181. Or if the second ray be at a right angle to
the one first projected, the result is an irregular quadrira-
diate figure, as represented by Fig. 180. In like manner
the irregular pentradiate form arises from the absence of
one of the four secondary rays, as in Fig. 1 82 ; or it some-
times occurs that the apical portion of the inequi-acerate
axial spiculum is deficient, and the result is, as represented
by Fig. 183, a regular pentradiate form. If the whole
of the radii are equally produced, the result is then the
regular attenuated rectangulated hexradiate spiculum,
(Fig- 174.)

Sometimes, but rarely, we find a single ray more or
less spinous at its distal end ; in this case it is probable
that it was attached by that point to the membranous
structure, or to some part of the keratode of the
skeleton.

The whole of these interesting spicula were obtained
from Mr. Cuming's specimen of Euplectella asperffillum,
Owen. They are abundant in that sponge, frequently
filling up the interstices of the network of the sihceous
skeleton, or otherwise entangled in the tissues. Jn
Dr. A. Farre's specimen of Euplectella cucumer, Owen,
they are equally abundant, and are not to be distinguished
from those in Mr. Cuming's specimen. They are, like
the great external prehensile spicula, and the fibre of
the skeleton, composed of numerous concentric layers of
silex, which readily separate from each other by decom-
position.

I cannot say with absolute certainty that this tribe
of spicula belong really to the sarcode, as I have never seen
specimens of either of the species I have named, in which
they occur in profusion, in such a state of preservation
as to allow of their position being positively determined ;
but as in another specimen of sponge with a siliceous
skeleton like that of Bactylocalyx pumicea^ Stutchbury,
the sarcode is preserved in excellent condition, and occurs
in such abundance, filling all the interstices of the skeleton



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64 ANATOMY AND PHYSIOLOGY

of the 8poDge, and affording ample space for the imbed*
ment of such spicula in its substance, I am, therefore,
induced to think it probable that a similar abundance
of sarcode may exist in Dactylocalyx and other similarly
constituted sponges, and that hereafter even the largest
of this tribe of spicula will be foun4 completely imbedded
in the sarcode.

Slender attenuated rectangulated hexradiate (Fig. 184,
Plate VII). — ^Beside the large and stout attenuato-
hexradiate spicula in Euplectella aspergiUum^ there are
comparatively small and very slender ones, many of which
are nearly of the same proportions as the larger ones ; but
generally speaking the axial radii are more elongated,
and in some cases the basal end is extended to four
or six times the length of the apical portion.

These spicula do not present the same irregularity in
their development that we observe in the stout ones,
and it is a rare occurrence to find one without the full
number of rays. They are exceedingly numerous in the
sponge, and they occur in closely packed fasciculi, the
axes of the spicula nearly touching each other. Amidst
these fasciculi we find the large stout forms imbedded, the
whole of them apparently having been completely enveloped
by the sarcode of the sponge.

Cylindro^rectangulated hexradiate : apically spined (Fig.
185, Plate VII). — This form is very abundant in an
undescribed species of Alcyoncellum in the Museum of
the Jardin des Plantes, Paris. The figure represents
the upper portion of the spiculum only, the lower portion
of the axial shaft being exceedingly elongated. When
examined with a power of 400 linear, the apices of the
radii are seen to be abundantly, but minutely spined.
The axial shaft of this spiculum, without any of the lateral
radii developed, is also abundant ; it is exceedingly long,
and at the proper distance below the apex we often observe
a gradual enlargement of the diameter, as represented in
Fig. 187, and the rudimentary canals for the lateral radii
are frequently apparent.

This form of spiculum is also very abundant in Dae-



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OF THE SPONGIADiE. 55

iylocalyx pumicea^ Stutchbury, Iphiteon of the French
Museum. In general character they are very similar to
those of the Alcyoncellum described above, with the addition
of the apices of the radii being more or less elevated.

All the simple rectangulated hexradiate forms of spicula
hitherto described are large compared with the rectan-
gulated hexradiate spicula which form the central bases of
the compound stellate forms, and excepting the disparity
in size, the transition from the last form described, to the
complicated and beautiful compound stellate ones, is easy
and natural ; the apices of the hexradiate form becoming
the bases of the numerous radii of the stellate ones. This
transition from the simple to the compound forms is
admirably illustrated in a bifurcated spiculum that occurs
in the new species of Alcyoncellum in the Museum of the
Jardin des Plantes. This form I have designated bifurcated
rectangulated hexradiate stellate, represented by Fig. 188,
Plate VIII. The next stage of development is when we
find each ray of the simple rectangulated hexradiate
spiculum terminated by either three, four, or eight symme-
trically disposed spicula, as represented by Figs. 189, 190,
191, and 192, Plate VIII, and their terminal secondary
radii are either acute or spinulate.

A still further amount of development is apparent in
the beautiful Floricomo hexradiate form represented by
Figs. 193 and 194, Plate VIII.

The central radii consist of six rectangulated primary
rays of equal length, with slightly expanded terminations,
from each of which there issues seven or more petaJoid
secondary spicula, the whole forming one of the most
beautiful simulations of a flower imaginable.

Each petaloid spiculum is slender at its proximal termi-
nation, and continues to be so until near its distal end,
where it expands laterally, and presents a nearly semi-
circular concavo-convex termination, with a beautiful
dentate margin, the number of the dents being usually
seven. Each of the petaloid spicula curves gently outward
from its base, the flowing line returning towards the
central axis of the flower at about half of its height from



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66 AXATOMY AND PHYSIOLOGY

the base, and then it again corves* outward, until the
apical expansion is at right angles to the floral axis ; so
that the whole resolves itself into a form like that of the
flower of a Jasmin. The beautiful terminal petaloid
expansions, with their regularly disposed mai^nal dents,
renders the illusion complete; the united basal curves
looking as if they had been produced by the swelling
ovarium of a flower.

I have obtained a considerable number of these elegant
spicula from my friend Mr. Cuming's beautiful specimen of
Eupleclella aspeTgUlum^ Owen, which, with his accustomed
liberality, he placed at my disposal for examination. They
are found also in Dr. A. Farre*s specimen of EuplecteUa
cucumeTj Owen, agreeing in every respect with those from
Mr. Cuming's sponge.

Generally speaking, the slender rectangulated hexradiate
spicula occur singly, but I have sometimes found them
grouped together ; in this case their axes were coincident
and their radii in the same plane, or very nearly so, but not
always agreeing in their direction ; such a framework would
form a very fitting support to a large mass of sarcodous
tissue partially separated from the framework of the skeleton
and occupying a portion of a large interstitial space.

In the large open areas of the skeleton of EuplecteUa
aspergiUumy Owen, the hexradiate forms, ranging from
Figs. 174 — 183, Plate VII, are exceedingly abundant, and
a considerable number of them are not developed to
the extent of the full number of their radii. This may
probably arise from the development of the radii being
stimulated by the necessities of the mass of sarcodous
tissues in which they are imbedded, and consequently
where no necessity for their presence exists they would
not be put forth. In the trifurcate and quadrifurcate
hexradiate forms, if we may judge from the termination
of their radii, they, like the simple stellate forms, are either
purely consolidating, or they combine with that office that
of defensive spicula also, as far as regards the sarcodous
substance in which they are imbedded.

We can scarcely imagine any defensive properties in the



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OF THE SPONGIAD^, 57

slender and complicated but elegant forms of the floricomo-
stellate spicula, and it is probable that their office is purely
that of assisting in the consolidation of the sarcodous
substance.

The whole of these beautiful stellate forms of spicula are
siliceous, while their homologues in the Gorgoniadae and
the compound tunicata are calcareous ; and it is somewhat
remarkable that hitherto none of these forms have been
found in the calcareous species of sponges.

Spicula of the Ovaria and Gemmules,

We find the same laws in force regarding the spicula in
the structure of the minute bodies which have been
designated gemmules by previous writers on the Spongiadse,
that obtain in the sponges themselves. In some they
serve the purposes of internal skeleton and defensive
spicula as weU. In others they combine the offices of
tension aud defensive organs, and frequently, they are very
difierent in form from those of the parent sponge. They
occur in various modes of disposition.

1. Those which have the spicula disposed at right angles
to lines radiating from the centre of the ovarium to its
surface.

2. Spicula disposed in lines radiating from the centre to
the circumference of the ovarium.



Online LibraryJames Scott BowerbankA monograph of the British Spongiadæ → online text (page 6 of 25)