THE FAUNA ASSOCIATED WITH THE CRINOIDS OF A 
TROPICAL CORAL REEF: WITH ESPECIAL REFER- 
ENCE TO ITS COLOUR VARIATIONS. 
By F. A. Ports, M.A. 
INTRODUCTION. 
Although so much attention has been devoted to the phenomena of 
mimicry and protective resemblance displayed by land animals, in only 
one case has the colour resemblances of a marine animal been exhaus- 
tively studied. I refer to the classical instance of Hippolyte varians, 
illustrated by a long series of ingenious observations made by Gamble 
and Keeble. Briefly stated, the story is as follows: The young Hippo- 
lyte is free-swimming and colourless, but it becomes virtually a seden- 
tary animal, anchoring itself to a seaweed or hydroid in the Laminarian 
zone, on which it finds both food and shelter. The prawn has the 
power of forming red, yellow, and blue pigments and by altering their 
relative proportions in the chromatophores it can acquire a green, 
brown, blue, or red ground-colour, and is thus able to adapt itself to 
the varied colours of the seaweeds and hydroids. The pigment may be 
laid down in longitudinal stripes or horizontal bars and in this way a 
colour scheme can be formed matching whatever seaweed the prawn 
shelters in. In early life a change in habitat is followed by a readjust- 
ment of the pigment altering the colour scheme, but this power is 
soon lost. 
There are, however, a great number of cases where species of small 
marine animals are associated with an environment not varying, as in 
the case of Hippolyte, but definitely fixed for the species—for instance, 
some particular kind of sedentary animal, sponge, alcyonarian, or 
crinoid, as the case may be, which it frequents for shelter and commonly 
resembles in colour. Sometimes the first is definitely a parasite on the 
second, as in an example of the phenomenon often noted at Murray 
Island, where the bright blue starfish Linckia laevigata, so widely spread 
on the Indo-Pacific reefs, was a source of food to multitudes of tiny 
copepods (Linckiomolgus cwruleus Stebbing), whose colour exactly 
matches that of the host, though the pigment is of a different chemical 
nature. 
