SOME COMMENSALS OF INDIAN ALCYONARIANS AND CRABS. 
By 
James Hoknell, F.L.S., F.R.A.I. 
(With 6 text figures.) 
No group of marine animals is more prone than the Alcyonarians to harbour 
uninvited guests, often of very varied zoological standing. Indian Alcyonarians 
or ‘ Soft Corals’ as we may dub them in common parlance, are exceedingly 
variable in form, ranging from the brick red Sea- whip, Juncella juncea, through 
the great assemblage of the Sea-fans, the Gorgonids proper, to the massive Sea- 
cauliflowers of which Spongodes is the tj'pe ; besides these are the Sea-pens — the 
thin starved rods of Virgularia, the pinnate fleshy Pennafula, typical of the group, 
and the great soft obese Cavernularia that Lives gregarious in muddy sand. 
Those that are greatly branched, offer the best shelter to small animals looking 
for safe hiding places and so it happens that Spongodes and its near relatives 
harbour a greater variety of commensals* than any other marine organism. 
The Commensals of Spongodes . — The common form of Spongodes met with in 
Indian seas lives from low tide level (Gulf of Kutch) to depths of about 10 
fathoms. It is particiJarly common in 5 to 8 fathoms in the Pearl Bank region 
of the Gulf of Mannar ; the dredge and the divers bring it up in dozens when the 
right spot, fairly clean sandy ground, is met with. The term sea-cauliflower 
which, for want of any accepted English name, is what I propose to call it, 
gives an accurate idea of the general appearance of a well-grovTi typical colony, 
if we imagine all the outer leaves tom away and the terminal florets tinted some 
bright colour from yellow and orange to pink and dark lake. Each colony 
has a short massive stalk or rather trimk, giving off numerous branches which 
divide and subdivide till the terminal branchlets are reached, on which are set 
innumerable little polyps, white or lemon tinted, each protected by a collar of 
defensive coloured spicules. The whole is rooted in the sand by means of many 
sand-encrusted ‘rootlets’. The substance of the trunk and branches is permeated 
by a system of numerous wide canals and bj’ means either of flooding or partially 
draining these by the action of a net -work of fine muscles fibres, the colony is 
capable of assuming very different forms ; it may expand freely, spreading wide 
and loosely its many branches — its normal condition — or it may retract into a 
compact nearly solid mass if irritated, with every gradation between the two 
extremes. Preserved specimens exhibit many of these gradations, dependent 
upon the method of killing and the time that has elapsed between captrrre and 
preservation. This, in conjunction with the natural great variability of the 
common species, has landed systematists in difficulties. On the one hand we 
have lists of 80 or more species, and on the other, the opinion of such an able 
zoologist as Prof. Sydney J. Hickson, that possibly there is otrly one true species 
to which all the 80 may be referred. 
The conrmonest form of Spongodes on oirr pearl barrks is one where the ter- 
minal branchlets are suffrrsed some tint of red, usually a warm dark pink, the 
trunk (excepting the base which is dirty grey) and the main branches being white. 
This form approaches most closely to the species (? varieties) described by Prof. 
J. A. Thompson under the names Spongodes bicolor and S. pulchra. 
If specimens of this species be examined as soon as they are brought up by the 
dredge or by divers, a host of symbiotic animals can be located hiding among 
* To be strictly accurate, I ought to say .symbiotic organisms, for the term com- 
mensals should be restricted to animals that live together in partnership and share 
the same table. But in this paper I use it in a somewhat loose way as a convenient 
word to cover all animals that lodge with another and are not definitely parasitic. 
