Fauna Associated with Crinoids of Tropical Coral Reef, etc. 93 
In conclusion, this species is quite distinct from, though related to, 
Polynoé crinoidicola, a species found on various unnamed crinoids in 
the Maldives by Professor Gardiner and described by mein 1910. The 
differences lie in the shape of the head and the tentacles and in the neu- 
ropodial setz, but the general facies and the character of the elytra and 
the shape of the parapodia and of the dorsal setz are similar. The 
specimens of crinoidicola are spoken of in one case as coming from a 
black crinoid and being themselves black when alive, though the pig- 
ment has dissolved out in alcohol. In other cases where the colour of 
the live animal and the host were not stated, the specimens were dark 
red. It seems certain, then, that the same type of colour resemblance 
occurs in the two species. In Torres Straits, too, I found the com- 
mensals always of a dark, almost black appearance and frequenting 
dark-coloured crinoids. They must, I think, be absent or rare on the 
lighter coloured hosts. 
The only other reference of which I have knowledge to commensalism 
between a polychete (?) and a crinoid is in Alcock’s ‘‘A Naturalist in 
Indian Seas,” p. 113, where he mentions a ‘‘sea-lily (Actinometra) 
striped in alternate bands of yellow and purple, on whose fronds simi- 
larly striped crustaceans live without fear of detection; which in some 
places also gives “‘secure shelter to seaworms, banded yellow and 
purple like itself.’’ This indicates a much wider range of pigmentation 
than in the present case. The banding is probably longitudinal, as in 
all other cases of commensalism. 
THE COLOURATION OF THE MYZOSTOMIDS AND ITS RELATION TO 
THAT OF THEIR HOSTS. 
From time to time remarks have been made on this subject. Semper* 
relates that he found his M. tuberculosum, which is spotted with red and 
yellow, only on variegated Comatulas, while the uniformly coloured 
M. cirriferum is found only on the red Comatulas, which it matches in 
colour. Von Graff,; however, remarks that though M. glabrum has a 
number of pronounced colour varieties, and the host Comatula europea 
s. mediterranea varies within the same limits and almost with the iden- 
tical shades of colour, yet his experience leads him to deny that any 
such definite mimicry relation exists between crinoid and myzostomid. 
A special investigation of over 200 comatulids showed that blackish, 
yellow and white myzostomids were just as frequently to be found on 
red Comatulids as blood-red myzostomids on variegated comatulids, 
and that the two kinds specially mentioned by Semper are uniformly 
distributed on the different colour varieties of the crinoid. 
*Semper, Zur Anatomie und Entwickelungsgeschichte der Gattung Myzostoma. Zeits. f. wiss. 
Zool. Bd. rx, pp. 48-65, 1858. a4 : 
tvon Graff, Das Genus Myzostoma. p. 77, Leipsig, 1877. 
