James Scott Bowerbank.

A monograph of the British Spongiadæ online

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the normal mode of defence, and almost induces the belief
that it was intended that such intruders as effected an
entrance were meant to be retained, and their decomposed
particles appropriated to the nutrition of the sponge. In
other cases, where no definite form of defensive spiculum
forms a part of the sponge, the office of those organs is
frequently performed by the projection of spicula similar to
those of the skeleton into the canals and cavities of the

If I were to attempt to enter upon a description of
every variation in the mode of the application of spicula
to defensive purposes, it would extend this portion of the
subject to a greater length than we can afford under the
present circumstances. I shall therefore confine my
observations- to a description of the general principles of

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defence as exhibited in some of the principal genera of the

In the external defences, the mode of the application of
the spicida depends in a great degree on the structure of
the skeleton of the sponge. The most simple cases are
those where the structure of the skeleton consists of spicula
radiating from the centre or the axes of the sponge, and in
these cases they usually consist of the terminations of the
radial lines of the skeleton, the distal spicula of which are
frequently projected for a considerable part of their length
through the dermal membranes, and in many sponges the
surface is thus thickly studded with them ; and in species
where the terminal radial lines of the skeleton contain
many spicula, they are frequently found at their apices to
assume a radiating direction, so as to present the greatest
possible number of points to their external enemies. This
mode of defence is very general in the numerous British
species of the genera Isodictya and Chalina, Bowerbank.
Fig. 287, Plate XVII, represents a small portion of a section
at right angles to the surface from Chalina seriata, Bower-
bank, illustrating very distinctly this simple mode of
external defence.

In the genus Dictyoct/lindrus, Bowerbank, which con-
sists principally of slender branching sponges, many of
which in their living state are exceedingly fleshy in then*
appearance, the skeleton is formed of a central cylinder,
composed of a network of spicula, from the surface of
which radiate in vast quantities long, slender and acutely
pointed spicula, which in the living condition project
slightly beyond the dermal membrane of the sponge, so
that in the event of any small fish attempting to feed upon
or suck this tempting bait, instead of a mouthful of soft
and grateful gelatinous matter, he would find himself
assailed in every direction with an infinite number of
minute points, many of which he would carry away with
him deeply imbedded in the soft lining of his mouth, as
the reward of his temerity and a warning against a repe-
tition of a like assault. Fig. 365, Plate XXXII, represents
a small portion of a young branch oi Bictyocylindrmruffostis,
Bowerbank, frequently found on shells and stones dredged

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up at Shetland, or the Orkney Islands. In the genus
TetheUy in which the skeleton consists of fasciculi of large,
stout spicula radiating from the base or centre of the
sponge, the system of defence is somewhat more compli-
cated. It is a combination of the terminations of the
skeleton fasciculi with, in some species, the addition at the
surface of the sponge of porrecto-ternate and recurvo-
ternate spicula; the latter two forms being probably
aggressive as well as defensive, subserving the purpose of
entangling prey as well as that of defence.

This mode of defence is very beautifully illustrated in
Tethea cranium. Fig. 362, Plate XXXI. The distal ends
of the skeleton fasciculi, composed of large fusiformi^
acerate spicula, are projected through the stout coriaceous
surface of the sponge, and in the midst of this thick coat
each of the passing fasciculi is surrounded by a cluster of
stout short fusiformi-acerate spicula, their distal points
closely embracing the fasciculus, while their proximal
terminations are spread widely out in a circle around the
lower part of the skeleton fasciculus at b, so as to form a
strong and most efficient conical buttress to sustain it in
its proper position, at the same time allowing a considerable
amount of elasticity to meet pressure from without. Each
skeleton fasciculus terminates with from two to eight or ten
porrecto-ternate spicula, and occasionally we find one or
two of the recurvo-ternate ones accompanying them ; but
their apices are rarely projected much beyond the dermal
membrane of the sponge, while the rest of the spicula
extend considerably above it. The same system of defences
prevails also in Tethea similima, Bowerbank, MS., from the
Antartic regions; but in this species the recurvo-ternate
spicula appear to be protruded in greater numbers, and in
more regular order than in our northern species, T. cranium.

In Tethea muricata, Bowerbank, MS., the skeleton
fasciculi are not protruded beyond the surface, but imme-
diately beneath it we find the heads of numerous large
furcated expando-temate spicula, with remarkably long and
acute terminal radii, while the dermal membrane is pro-
fusely furnished with attenuato-elongo-stellate spicula,
Figs. 304 and 305, Plate XIX.

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In Tethea Norveffica and IngalU, Bowerbank, MS., and
in T. lyncurinm, Johnston, the same protection is attained
in a different manner. Instead of the spicnla of the
skeleton fasciculi gradually converging towards a point,
they diverge considerably as they approach the surface, so
as to present an infinite number of minute and nearly
equidistant points, and in addition to these the dermal
membrane and the coriaceous coat of the sponge is supplied
with an infinite number of closely packed stellate spicula.

In some species of the genus Geodia the system of
external defences is still more complex. Thus in G,
McAndretcii and G. Barretti the defences are double, one
system consisting of a continuation of the great radial
fasciculi of the skeleton as a protection against the assaults
of the lai^er and more powerful assailants ; and then of a
secondary series consisting of an infinite number of minute
acerate spicula, based immediately beneath the dermal
membrane and projecting to a slight extent beyond its
external surface, effectually protecting it and the porous
system of the sponge from the attach of itS minute and
more insidious enemies.

Similar modes of external defences exist in various
species of Pachymatisma and Bcionemia, but no two
species appear to agree precisely in these respects.

In the genera Microciona and Hymeraphia, Bowerbank,

differing widely in the structure of their skeletons from any

of the sponges hitherto described, and frequently not

exceeding in thickness the substance of a stout sheet of

paper or a thin card, the same principles of defence are

carried out, although their structure is widely different

from each other. In the first genus, the skeleton of which

i of short pedestals of keratode combined with

each of the pedestals, which reach nearly to the

3f the sponge, is terminated vnth a radiating

)i long curved and acutely-pointed spicula, the

■ which pass through the dermal membrane in

rection, and thus form a most effectual series of

defences, while their shafts beneath serve as the

k of the intermarginal cavities of the sponge

^8, Plate XXXIII, and 369, Plate XXXIV). In

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Hyineraphia, where the sponge is less in thickness than
the length of one skeleton spiculum, and where they pass
from the basal membrane of the sponge through the
dermal membrane, their apices acting as external defensive
organs, while their shafts form the essential skeleton of
the animal, there is an especial provision for their pre-
servation from injury. Their bases are expanded in the
form of large bulbs, so as not only to afford a greater
surface for attachment, but to allow them at the same time
to act on the principle of a ball-and-socket joint, giving
them a more than usual amount of attachment, and a
power of yielding in every direction to pressure on their
apices from without (Fig. 370, Plate XXXIV). The
defence of the surface of the Halichondroid sponges is
less app^ent, but equally efficacious ; the abundantly
spiculous reticulations immediately beneath and supporting
the dermal membrane, would render attacks of annelid
or other small predaceous creatures exceedingly im-

In the calcareous sponges the spicular defences are
exceedingly interesting. In Grantia compresaa^ the distal
ends of the great interstitial cells are amply protected
by numerous flecto-attenuato-acuate spicula grouped
around their porous terminations, with their club-shaped
ends curving in every direction over them, but in no
degree interfering with the 'freedom of their inhalant action.
In Grantia ciliata they are grouped in circles around the
distal ends of the interstitial cells (Fig. 345, Plate XXVI),
but in this species they are acutely pointed ; and When the
inhalant system is in a state of repose, they are concen-
trated at their extreme points so as to form an elongate
cone, effectuaQy enclosing and protecting the porous ends
of the cells within them ; but when the inhalant action is
in full activity, their apices recede from each other until
they assume the form of a cylinder, and then freely admit
the incurrent streams of water, but effectually repel the
advances of any dangerous assailant that may attempt an
entrance. The distal termination of the cloaca in this
species is also abundantly protected by a marginal fringe
of long and very acute spicula, and is furnished with the

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same simple but beautiful mechanical contrivances for
opening and closing in accordance with the necessities
of the animal. For a more complete description of the
anatomy and physiology of this highly interesting species I
must refer my reader to the * Transactions of the Microsco-
pical Society of London/ vol. vii, p. 79, pi. v.

In other species of Grantia the same principles of
external defensive action exists, but the precise mode is
never exactly the same in any two species.

Their external defences are the homologues of those of
the dermis of some of the Holothuriada and of Synapta.
Thus in Cucumaria communis we have the dermis fur-
nished with an infinite number of beautiful perforated
circular plates, from the centre of each of these is projected
outward a spiculated umbo terminating in numerous acute
points ; when the animal is irritated the whole of these are
projected from the dermis and the surface becomes bristling
with an infinite number of minute organs of defence. In
like manner Synapta is furnished with numerous anchor-
shaped spines which lie parallel to the dermal surface while
the animal is in an unexcited state ; but when irritated a
muscular contraction of the dermis takes place, the shank
of each anchorate spine is drawn inward, forming a
minute pit or depression, so that it becomes erect, and the
sharply pointed flukes, if we may so term them, are brought
into defensive position over the whole surface of the body
of the animal.

Tnternal Defensive Spicula,

The internal defensive spicula of sponges are exceedingly
various in their forms and modes of application to their
especial purposes; and they seem naturally to resolve
themselves into three distinct groups : — 1st, those which
are destined simply to repel ; 2nd, those which wound and
lacerate as well as repel ; and 3rd, those which are calcu-
lated not only to destroy but also to retain intruders.

The purposes of the first class of spicula are frequently
performed by the ordinary spicula of the skeleton, which
are projected more or less into the cavities immediately

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within the oscula and other spaces requiring such pro-
tection ; but when especially formed for and appropriated
to defensive purposes, they are always free from spines and
usually terminate acutely; and they are frequently pro-
vided with widely extended basal radii, so as to fix them
rigidly and firmly in their proper positions, as exemplified in
the various forms of spiculated triradiate spicula represented
by Figs. 85, 86, and 87, Plate IV.

The best illustrations of the application of the simple
defensive spicula are to be found in the cloaca in several
species of Grantiay as in G, cUiata, Johnston, and G.
tessellata and ensata, Bowerbank, MS. In all these
species this great central cavity is abundantly furnished
with spiculated triradiate spicula, which are so disposed
that while the basal radii are firmly cemented on the
surface of the cloaca, the spicular or defensive rays are
projected from its surface, not at right angles to its plane,
but always at such an inchnation towards the mouth of
the cloaca as to present a combined series of sharp points
in the best possible position of defence, so that an
intruding assailant could scarcely escape being seriously
wounded by them, while a retiring enemy would pass
with impunity over their inclined apices. In some species,
as in G, tessellatay the defensive ray is naturally curved to
the desired angle for defence (Fig. 86, Plate IV), and it is
also of such a form as to be readily released from the
creature it has wounded, either by being attenuato-acuate
or ensiform, as in Fig. 85, Plate IV, from G. emata, and
as represented in situ by a small portion of a longitudinal
section of the cloaca of a specimen of Grantia tessellata
in Fig. 286, Plate I, in which the defensive radii are all
curved in the direction of the mouth of the cloaca.

In the second division the internal defensive spicula
are usually short and straight, and more or less covered
with strong conical acutely pointed spines, projected either
at right angles to the axis of the spiculum, or recurved
considerably towards its base; generally speaking the
spines are dispersed on all parts of the spiculum without
any approach to order, as represented in Fig. 66, Plate III,

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while in other cases, as in Figs. 67 and 68 in the sarae
Plate, they are arranged in verticillate order on all parts of
the spiculum. In each of these varieties the bases of
the spicula are usually profusely furnished with spines
so as to ensure a strong and somewhat rigid mode of

There is undoubtedly a special purpose in every variation
of the spination of these spicula, and in their presence
generally. The short strong form and acute distal termi-
nation admirably adapts them to encounter the larger
description of intruding annelids, the most dangerous
internal enemies of the Spongiadae; while the spination
of their shafts presents a series of minute weapons that
would prove equally formidable to those intruders that
were too minute to be affected by the larger weapons
of defence.

The acuate entirely spined defensive spicula are of very
common occurrence in sponges, and are by no means
confined to particular tribes or genera. As a general
rule, when the external defences are very full and suffi-
cient, we should not expect to find the internal defences
abundant, and, on the contrary, when there appears to be
a paucity of external defences, the internal ones are fre-
quently exceedingly numerous. Thus, in the genus
Dictyoc^lindrus, Bowerbank, where in almost every species
the surface of all parts of the sponge is bristling with the
acute terminations of the radiating external defensive
spicula, although in most of the species we find acuate
entirely spined internal defensive ones, yet in many of
the species they are so rare as to be by no means readily

When the skeleton is formed of keratose fibres, we find
them dispersed on their surface without any approach to
order, and projected at every imaginable angle. If the
skeleton be formed of any of the varieties of spiculous reticu-
lations, they are based in a similar manner on the prin-
cipal lines of the reticulated structure, and sometimes, but
not very frequently, they occur in groups.

I will not extend this portion of my subject to an

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unnecessary length by describing every mode of their
occurrence, but select a few of the most interesting
cases as illustrations of the general principles of their

Fig. 288, Plate XVII, represents a small portion of
the kerato-fibrous skeleton- of an Australian sponge, with
the attenuato-acuate entirely spined internal defensive
spicula in situ. Fig. 289, represents a few fibres from a
kerato-fibrous sponge from the West Indies, in which the
verticillately spined internal defensive spicula are dispersed
over the fibres ; and Fig. 290 represents the same descrip-
tion of defensive spicula from a West Indian kerato-
fibrous sponge, having the defensive spicula congregated in
bundles. Sometimes, but not very frequently, they are
found on the interstitial or basal membranes of the sponge,
and under these circumstances many of them are prostrate
in place of being erect ; and in one sponge, Hymeniacidon
Clt/toni, Bowerbank, MS., a singular parasitical species
from Freemantle, Austraha, this prostration appears to be
effected by an especial law. This singular sponge enve-
lopes several fan-shaped portions of a Fucus, and syste-
matically appropriates the minute ramifications of its stem
to the purposes of an artificial skeleton ; the whole sponge
abounds with short stout attenuato-cylindrical entirely
spined internal defensive spicula; but the remarkable
circumstance attendant on their presence is, that where-
ever the membranes supporting them envelope and firmly
embraces a portion of the vegetable stem, they assume an
erect position, and exhibit all the usual characters of
defensive spicula; but where the membranes merely fill
up the areas of the vegetable network, they are nearly
all of them perfectly prostrate and apparently performing
the office of tension, rather than of internal defensive
spicula. Their form also is singular, being attenuato-
cylindrical. not having the acute termination that is usual
in this description of spicula.

Fig. 291, Plate XVII, represents a small portion of the
fibrous stem of the Fucm coated by the membranes of the
sponge, and covered with spicula ; those immediately over

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the stem being erect, while those od the membrane are
prostrate, (a) represents one of these new form of internal
defensive spiculum X 175 linear and [b) a small portion of
the surface of the Fucus showing its cellular structure
X 400 linear.

In Hymeraphia stellifera, Bowerbank, an exceedingly
thin coating British sponge, the internal defensive spicula
present a singular variation from the normal form. In
this case they assume the shape of an ordinary PJorence
oil flask, with a somewhat elongate neck, and having a
beautiful star-shaped apex in place of a stopper. They
occur in considerable quantities ; their large bulbous bases
are firmly attached to the strong basal membrane of the
sponge, and they are projected thence at every possible
angle upward into the interstitial spaces. Their apices
are crowded with stout acutely conical spines, which
radiate in all directions. Fig. 730 a, Plate XXXIV,
represents a group of these spicula in situ^ elevated by
a grain of sand beneath the basal membrane ; and Fig. 34,
Plate I, one of the same form of spiculum, magnified 260
linear. In this form of spiculimi, as in that of Ilymenu
addon Cliftoniy their purposes seems to be the infliction
of laceration, rather than that of destruction by deep
wounds. In another species of Hymeraphia, H. clavata,
these spicula have the same large bulbous bases as those of
H. stellifera, but their apices are acute, like those of the
normal forms of such spicula. In all these cases we
observe in their attachments the same approximation to
the structure of the ball-and-socket joints of the higher
tribes of animals, rendering them capable of yielding in
every possible direction to the struggles of any enemy with
whom they may be entangled.

In the third division of the internal defensive spicula
there is an especial construction for retention as well as for
destruction. Their apices are usually more or less hamate,
as represented in Figs. 76, Plate III, and Figs. 81 and 82,
Plate IV, and their attachments to the sponge are usually
such as to allow of a considerable amount of flexibility
or motion.

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I will not attempt to describe the whole of the numerous
variations in the modes of application to defensive pur-
poses, but select a few of the most interesting cases as
illustrations of the general principles of combined internal
defence and aggression.

The spinulo-recurvo-quaternate spiculum (Fig. 76, Plate
III), presents an admirable illustration of the combined
defensive and aggressive character of some of those internal
defensive spicula. The sponge in which they occur
belongs to the Halichondroid tribe, the skeleton being
composed of a network of spicula cemented together by
their apices, which cross each other at the angles of the
areas of the reticulations. The recurvo-quatemate spicula
are not dispersed on all parts of the skeleton, but are
congregated in groups, frequently consisting of as many as
fifteen spicula, the whole of their bases being concentrated
on one of the angles of the reticulations of the skeleton,
while their shafts and apices radiate thence in every
direction into the interstitial spaces of the sponge ; they
are thus placed on the strongest and most elastic portion
of the skeleton, with their hemispherical bases firmly
imbedded in the cementing keratode of the skeleton,
which abounds at the angles of the network, and which
by its inherent elasticity and strength renders the insertion
of the base of the spiculum, in strength and extent of
action, quite equivalent to the powers of the ball-and-
socket joints in the higher tribes of animals. A small
anneUd or other minute intruder entangled amidst these
numerous sharp hooks would struggle hopelessly in such a
situation, as the spicula, f5pom the nature of their attach-
ment, would yield readily to its struggles in every possible
direction, and at every new contortion arising from its
efforts to escape it would inevitably receive a fresh series of
punctures and lacerations.

Fig. 292, Plate XVIII, represents a small portion of
the skeleton of the sponge bearing the spinulo-recurvo-
quartemate spicula in situ.

The gradual development of this form of spiculum is
interesting and very instructive. In an early stage of

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its development it has the appearance of a slender inequi-
biclavate cylindrical spiculum (as represented in Plate III,
Fig. 73) ; in the next stage there is a slight indication
of the spinulate base, and a corresponding amount of
expansion of the apex, but no indication of the radii
(Fig. 74). From this state to the next well-marked stage
of growth (represented in Fig. 76) the progressive develop-
ment of the radii may be readily traced, and thence to the
adult condition represented in Fig. 76.

In its fuUy-developed state we find a great increase in
its size in every respect ; the base becomes fully developed
and globular, and the radii elongated to a very considerable

In other instances, where defence alone appears to be
contemplated, we do not find these beautiful adaptations
for motion in every direction prevail. The bases of the
spicula in those cases are abundantly spinous, and are
evidently intended to maintain a firm hold by their
attachments, and are destined rather to rigidly maintain
their position than to yield to any struggling body with
which they may be in contact. The numerous spines with
which these shafts are frequently covered are calculated to
wound and lacerate, rather than to retain the enemies with
which they are engaged.

I have received from my friend, Mr. J. Yate Johnson, of
Madeira, a new and very illustrative instance of the combi-
nation of defence and aggression in the structure And
offices of the internal defensive spicula ; and in this case it
is not a new organ, but an adaptation of a well-known

Online LibraryJames Scott BowerbankA monograph of the British Spongiadæ → online text (page 4 of 25)