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Scientific Memoirs by

must be an equal advantage to themselves. That the polyps are not parasites is
proved by the facts (1) that the nutritive zooids of the colony have a proper
mouth and a prominent peristome fully equipped with tentacles for catching food,
and (2) that in any colony numerous zooids may be found with their gastric
cavity crammed with food, which they must have caught for themselves.

      In the following six cases of symbiosis, in which Zoophytes are concerned,
the element of reciprocity seems to be wanting, so that it is doubtful whether they
should be cited as cases of true commensalism:—

      (a ) The feeble little Oxyrhynch (Pisine) crab Hoplophrys oatesi lives among
the branches of the Alcyonarian Zoophyte Spongodes prox. pustulosa. The polyp
colony has a brilliant white coenosarc and pink-tipped zooids, while the living
crab is porcelain-white with pink spines on its carapace and pink-banded legs,
the colours of the two animals matching so completely that the crab escapes
notice. The advantage to the crab is obvious, and there can be little doubt that
the animal has been specially adapted to its habitat; but there seems to be no
corresponding benefit to the Spongodes.

      (b ) A parallel case is that of the little Xanthoid crab Liomera sodalis, the
red and yellow colour-markings of which are exactly those of the Alcyonarian
(Solenocaulon sp.) in whose hollow branches it dwells.

      (c ) The diminutive Thalassinoid lobster Iconaxiopsis laccadivensis, —a
pair (male and egg-laden female) of which were taken on the branches of the
Gorgonacean Zoophyte Calypterinus allmanni, is another instance of a feeble
crustacean escaping detection by closely resembling in colour the host with
which it lives.

      (d ) A Pennatulid Zoophyte of the genus Pteroeides, found in these seas,
gives similar cover to no less than three different kinds of lurking Crustaceans—
a Porcellana, an Alpheus, and a Crangonoid—all of which are specially modified
for their habitat. The coenosarc and zooids of the Pteroeides are of a trans-
parent grey colour, and each zooid is defined by a ring of dark grey pigment.
To match this exactly, the crustacean commensals are transparent grey marked
with spots and rings of dark grey.

      (e ) In stocks of the Oculinoid coral Lophohelia investigatoris, dredged off
the Travancore coast in 430 fathoms, numerous specimens of a Polychaete
worm were found, the connexion being undoubtedly a permanent one. The
worms were living, not like parasites inside the branches of the coral, but inside
tunnels formed by a crust of scleroderm that connected two neighbouring bran-
ches.

      (f ) In the branches of Calypterinus allmani, dredged in the Laccadive
Sea at 705 fathoms, several specimens of a slender Polychaete worm were