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474 COLLECTIONS FROM M E LA N E S IA .
in the arm. is not quite constant in its position. The rest of tho
characters agree Avith those of the typical form.
Hah. West Island, Torres Straits, 7 fms.; bottom sand.
Variations. This sponge varies, as has been seen, in shape (oval
or subspherical) and in the presence or absence of a vent. A third
variation may be noted, viz. in the length, stoutness, and amount
of curve in the arms, and in stoutness of the shaft of the zone-
spicule ; thus in a specimen from the Arafura Sea the diameter of
the shaft falls to -045 millim., th a t of the arms to '043 millim., the
length of the arm remaining ’25 millim., Avhile the backAvard bend of
the arm, though gradual, is very decided.
The variations in this spicule, which is the only one which seems
to differ much in different specimens, are as follows :—
Diam. of
shaft.
Diam. of
arm.
Length
of arm. Curve of arm
1. Port - Darwin specimen
..........................
2. Thursday Island specimen
.................... ..
3. Arafura - Sea specimen
..........................
4. Var. retroflexa (West
Island, Torres Straits)
millim.
•06
•05
•015
•04
millim.
•06
•05
•043
• ^04
millim.
•25
•27
•26
•33
slight, gradual.
decided, gradual,
sharp near end.
The stellate is only -013 to -017 miUim. in diameter in specimen
No. 3.
The species differs from S. hacca, Selenka, in the small size of the
stellate spicule, viz. •02--025 millim. instead of -2 to -4 millim. in
d iameter; from S. tethyopsis. Carter, in having no “ forks,” and
simple, not trifid, arms to the “ zone-spicule; ” and from S. gloho-
stellata, id., iu the absence of a globostellate spicule ; for distinctions
from other species see table of species above. The largest specimens
measure about 25 millim. (1 inch) in greatest d iameter; all the
specimens are preserved in spirit.
102. Stelletta clavosa *. ( P l a t e X L III. f ig s . i, i".)
Free, suhglobular (very occasionally suhoval). A single circular
vent is almost (if not quite) invariably p resen t; it is situate either
on a flattened or depressed area; its margin apparently forms a
sphincter ; diameter 2 millim. in the largest specimens received.
The excretory canals unite at 1-2 miUim. below surface. Colour, in
well-preserved spirit-specimens, pale purplish grey to puce, in others
* From clavus, a nail, in allusion to the fine nail-like zone-spicule.
SPON G IID A . TO
simply grey. A distinct cortical layer, containing the subcortical
crypts, and formed in adult specimens by the space between the
heads of the zone-spicules and those of the anchors, diameter about
•7 millim.; sarcode here of same consistency as in rest of sponge.
Sponge-sarcode below surface rather dark yellow-hrown, rather
granular; th at of surface (in well-preserved specimens) reddish
brown, granular.
Spicules;—(1) Zone-spicule, with long shaft tapering gradually
from head to sharp p o in t; head composed of three bifid arms ; the
proximal third of each arm projects forAvard at an angle of about
120° to the shaft, and then bifurcates in a plane parallel to th a t of
the surface of the sponge, so that the ultimate divisions are parallel
with this surface; the ultimate di\dsions taper gradually to sharp
points from the point of bifurcation; shaft about 3 millim. long by
•035 millim. in diameter; total length of single arm -32 millim., of
proximal (simple) part •! millim.; diameter of proximal part
throughout ‘028-'032 millim., of base of ultimate divisions about
the same. (2) Anchor, with long shaft tapering gradually from
head to sharp point, and head composed of three arms tapering
gradually to sharp points, curved backwards to form angles of about
45° with shaft (the angles vary slightly in different specimens) ; shaft
about 2'1 millim. by ‘022 to '024 millim. ; expanse of arms • !! to
•12 millim., diameter of arm at base about -02 millim. (3) Body
acerate, long and slender, smooth, tapering gradually to sharp
points from the centre ; size about 3 hy -025 millim. (4) Flesh-
spicule, composed of about 7 to 12 straight arms, radiating from a
centre which does not shoAV any perceptible inflation ; arms very
slender (about ’0008 millim. in diameter), terminated hy heads of
about twice their own d iameter; spicule -Ol to -013 millim. in
diameter across the a rm s : distributed generally in sarcode.
Hah. Prince of Wales Channel and West Island, Torres Straits,
7 -9 fm s.; bottom sand and coral. Arafura Sea, off N.W. coast of
Australia, 32-36 fms. ; bottom sand, mud, and shells.
This appears to he a small species, none of the specimens exceeding
13 millim. in their longest diameter. I t exhibits, as compared
with S . purpurea, a remarkable constancy in its form and
in the occurrence of a vent, and the spicules vary hut slightly in
form and dimensions (the only variations observed are incorporated
with the description above). In Torres Straits very few
specimens were obtained; but in the Arafura Sea a considerable
number of small specimens occurred. Stelletta clavosa differs
from all nearly allied forms except S. tethyopsis. Carter, in the
bifurcation of the arms of the zone-spicule, and from the latter
species hy the absence of “ anchors ” and of an external as distinguished
from an internal form of stellate. The arms of the zone-
spicule are much longer in proportion to their thickness than in
Carter’s species.
Parasite. In the superficial sarcode (probably ju st beneath the
ectoderm) of one specimen occur a large number of a chain-hke
Alga, resembling Nostoc, usually coiled, with very distinct cells.
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