SOME COMMENSALS OF INDIAN ALC YONARIANS. 
929 
In species of Spongodes of more lax growth such as S. dendrophyta, where the 
stem is markedly elongated, I have never found Dromia present. The habit 
of such species would appear to make it less fitted for concealment than in 
Spongodes pvlchra ; the association also appears local in its range, for while 
common over a considerable area off the Ceylon coast in the pearl bank region, 1 
have’ never found it to occur on the Indian side, where the same species of 
Spongodes is equally abundant. 
The Commensals of Solenocavlon tortuosum. Gray. — This species is common 
in depths of 8 to 9 fathoms on certain coarse sandy ground off Tuticorin, parti- 
cularly in the vicinity of the pearl bank known as the Melonbadu Par. It is 
perhaps the most handsome of Indian Alcyonarians, consisting of a strong stalk 
rooted at its base in the sand, the projecting part a foot and even more in length, 
the whole suffused with shades of pinkish red. Frequenth^ the stalk, at a height 
of a few inches above the ground, divides into two main branches, broad and 
foliaceous in appearance, giving off again secondary branches even more foliace- 
ous, which in turn give off numerous stout terminal branchlets, bearing most ele- 
gant yellow tinted po]}’ps. The stalk except at the base is usually tubular, 
as are also usually the primary branches. The secondary branches may be 
either tubular or merely grooved. Variation in form is however extreme and all 
possible modifications may be met with both in branching and in the extent 
of tubulation. In some, the tubular character is even restricted to the stalk ; 
in others it extends only into the primary branches, the remainder being grooved 
in varying degree from a slight inturning of the margin to a deep semi-circular 
gutter. On account of this great variation Prof. S. J. Hickson* united all the 
previously described species into one, and I consider he is correct in this attitude. 
He was also the first to put forward the theory that the origin of the tubulation 
of the stalk and branches is due to the constant irritation caused to the tissues by 
the running backwards and forwards of symbiotic crustaceans belonging to the 
genus Alpheus. Hickson notices the presence of these Uttle prawns in the tubular 
portions of many of the jireserved specimens from the Maldives which came 
under his examination. He hazarded the suggestion that the tubular character 
of Solenocaulon is “of the natme of a gall produced by an active crustacean and 
that the degree to which it affects the secondary and tertiary branches depends, 
not upon any inherent specific character of the Solenocaulon, but upon the 
number or activity of the symbiotic Crustacea.” He instanced the weU-known 
fact that in such corals as Pocillopora, Seriatopora, and Millepora, which often 
harbour a sjunbiotic crab, its presence affects growth at the place where it 
settles and there induces the formation of a spherical or oval gall, “ the margins 
of the affected part being hypertrophied and growing round and enclosing the 
animal that causes the irritation”; analogous gaU-like grow'ths are produced on 
the branches of various corals and gorgonids bj"' the settlement thereon of various 
species of cirripedes, whose presence causes a local disturbance of normal 
growth. He pointed out also how the hypertrophied surfaces in such cases 
show a smoothness of surface, and in Millepora, an absence of polyps 
of the same character as is exhibited by the grooved surfaces of the branches 
and terminal twigs of Solenocaulon. The new evidence which I have adduced 
above showing how similar and even greater tubes are formed in the related 
genus of Spongodes, goes far to prove the vahdity of his main inference. 
My observations show however that other animals live symbiotic lives with 
Solenocaulon, besides the Alpheid rrentioned by Hickson. The principal 
of these comprise an Anoraurid, a Porcelain-crab and, most interesting of 
all, a tiny Gobioid fish of an hitherto undescribed sjx^cies of the genus 
Pleurosicya. 
* “ The Alcyonaria of the Maldives” in The Fauna and Geography of the Maidive 
and Laccadive Archipelagoes, Vol. II, Pt. II, Cambridge, 1903. 
