60 Mr Potts, The Colour Variations | 
totally covered with dark pigment, while in Cirolana, on the other | 
hand, the individuals associated with even the darkest crinoids, | 
possess only insignificant lines of pigment on the otherwise totally 
white body. In the latter case then there is no protective resem- | 
blance although we witness the incipient stages of its establishment, | 
Other forms like the polychaet, the amphipod and the brittle star | 
Ophiomesa only possess dark varieties and occur upon dark green / 
or black crinoids. | 
The most constant commensals of Comanthus annulatum are the « 
two species of Synalpheus. SS. Brucer was found in great numbers ‘ 
| 
: 
: 
Fig. 1. Synalpheus comatularum Haswell. x2. To show colour pattern. | 
eta euialler chela, the finger of which is modified for temporary fixation to ) 
e host. 
on the crinoids from the reef at Murray Island ‘but at depths of | 
about five fathoms it is largely replaced by S. comatularum. In \ 
both species the habits of the Alpheid and its colour variations are © 
similar. ach crinoid harbours a pair, male and female, which sit - 
side by side on the dise, with their heads directed toward the mouth. © 
When disturbed they cling firmly to the host, in S. Brucei digging 
the apical spines of the thoracic feet into the soft flesh of 
the disc while in S. comatularum the extraordinarily modified 
thumb of the smaller chela is hooked into the flesh or round a 
pinnule of the crinoid. When hunted off the dise they seek refuge 
on the under surface of the arms and when detached from the 
crinoid speedily return to its shelter. In addition they are re- 
markably thigmotropic, gathering together in an inextricable mass 
when kept in the same vessel. 
