SOME COMMENSALS OF INDIAN ALCYONARIANS. 
927 
the branches ; the list includes at least a couple of brittle-stars, several crusta- 
ceans including a galatheid, a porcelain-crab, a clicking prawn, a colourless 
compound ascidian and a tiny little cowry. A sipunculid worm is often present 
among the anchoring rootlets, while last and most interesting is one of the 
velvet-crabs, belonging to the family Drojniidce. 
Omitting the last two, the others with the one exception of the alpheid, have 
the body ordinarily speckled, spotted or mottled with some tint of red. 
The most numerous of these uninvited guests is the little porcelain-crab, 
Porcellana quadrilobata. Several of these are usually met with in each colony, 
the yoimger and smaller either colourless (white) or faintly speckled with red, 
while the larger generally have the carapace well mottled with pink. Both colour- 
ations are protective as the white ones harmonize with the colour of the trunk and 
branches, while the pink-mottled are easily lost to sight amongst the pinktipjoed 
branchlets. The graceful Galatheid, Polyonyx hmnguiculatus, is also sometimes 
found, its upper surface mottled reddish brown. The Ophiuroid and the Cowry 
are still more distinctively blotched with red, and both seem to be consistently 
associated with this pai ticular species of Sj)ongodes for T have never seen them 
elsewhere. They are not however always present and they seem local in oc- 
currence. For example, out of 14 spongodes examined on one occasion on the 
Ceylon banks, 10 had this ophiuroid, while of 12 examined a few days later from 
the same depth of water (5 to 6 fathoms) but from a locality a few miles distant, 
in no case was this ophim’oid seen. It is a smooth -armed species of fair size ; 
the disc measures 10mm. across, the arms 3^ to 4^- inches in length. It lies 
securely lodged among the branches, the long arms twining ivy-like in and out 
among them. In colour it is whitish, with five groups of pirdcish red blotches 
on the aboral surface of the disc, and with band-like splashes of the same colour 
at regular intervals on the upper surface of the arms. The rmder surface is 
uniformly white. The upper surface of the aixus is actually in no place quite 
without red pigment ; tin}' points of red occur over the whole surface, but at 
fairly evenly spaced intervals they are greatly increased in number and this 
massing gives rise to the appearance so characteristic of this species of having 
the arms regularly banded with pinkish red. In some individuals the general 
pigmentation is much more intense than in others but it can be made out in all 
when they are carefully examined. When moving about over the host’s branches 
this scheme of colouring harmonizes effectively with the pinli and white of the 
terminal polyp-bearing twigs. 
The last of the commensal cmstaceans, the clicking-prawn, Synalpheus gravieri, 
never exhibits any red spotting. This is no disadvantage to it, for it is too 
large, active and pugnacious to fear any animal that is small enough or brave 
enough to penetrate within the spicule-beset branches of the host. In any 
case its pale white tint does agree with that of the inner recesses of Spongodes. 
Then there is the tiny little spotted Cowry (Cypraea). It lives among the 
outer branches where there is a good deal of mottled reddish coloming. Its 
mantle, normally reflected over the whole of the shell, is accordingly spotted 
red, harmonizing exactly with the red and white mottling of its host. The 
shell itself is marked with a few large brown blotches, quite different from 
the numerous small red spots on the mantle ; as the latter enwraps the shell 
completely, the colouring showu to the world of its enemies is that of the 
mantle. 
Normally the trunk of this species of Spongodes is entire and solid looking, but 
a considerable proportion of large-sized individuals from one particular area of 
the Ceylon Pearl Banks, namely the sandy ground to the east of the Cheval 
Par and around the Moderagam Pars, where it is particularly abundant, have 
either deep pockets in the upper part of the trunk, or have wide tubes passing 
down this main axis. These cavities do not communicate in any way with the 
intrinsic canal system of the Alcyonarian. In many instances the open central 
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