Mr Potts, The Colour Variations of the Fauna, etc. 59 
The Colour Variations of the Fauna associated with Crinoids. 
‘By F. A. Ports, M.A., Trinity Hall. 
: [Read 23 November 1914.] 
Although a number of animals have been previously described 
as living on crinoids and matching their hosts in colour no complete 
study of this commensal fauna has been made. During a visit to 
‘Murray Island, Torres Straits, in October 1913, I was able to make 
‘some observations on the wonderfully rich crinoid fauna on the 
reefs there. The commonest species is a form called Comanthus 
annulatum Bell remarkable for its extraordinary range of colour 
variation from very light coloured individuals in which white, light 
green, yellow and grey mingled in the colour scheme to others 
which are entirely dark green or black. In the shelter of its arms 
live commensal forms belonging to many groups of marine in- 
vertebrates and generally speaking they possess a type of coloration 
which makes them inconspicuous upon the host and so varies with 
the colour of the host. 
The commensals so far as they have been identified are given 
in the following list: 
CRUSTACEA. Decapoda Macrura. Synalpheus comatularum 
Haswell, S. Brucer sp. n.*, Periclimenes 
spp. n.t and a new genus (Pontoniopsis) and 
species of Pontoniid prawnst. 
Decapoda Anomura. (Galathea longirostris 
Dana and two new species of Galathea. 
Isopoda. Ctrolana sp. n. 
Amphipoda. A new genus of the family 
Amphilochidae. 
ECHINODERMATA. Ophiuroidea. Ophiomesa cacaotica and _ pyo- 
bably other species of brittle stars. 
ANNELIDA. Polychaeta. A form probably near Polynoé 
minuta Potts. 
Myzostomidae. A number of species. 
The different commensals have responded in different degrees 
to the stimulus causing this colour resemblance to their host. 
Thus among the Crustacea, in Synalpheus all stages of variation 
are met with, according to the individual inhabited, between a 
pale form with very narrow stripes of pigment to an extreme form 
* Probably the whole comatularum group of the genus Synalpheus are associated 
with crinoids. 
+ A number of species of Periclimenes have been described from erinoids. 
+ Mr L. A. Borradaile is publishing a description of Pontoniopsis and the new 
species of Periclimenes in a forthcoming revision of the Pontoninae. 
