1064 MR. OYRIL CROSSLAXD ON , 



Two interesting facts are worth recording of the coloration of 

 several species of Tectibranchs, which besides being close simu- 

 lacra of their environment in other respects, each occur in green 

 and brown va,i'ieties, simulating green or brown weeds, or at least 

 in one case, the old and young shoots of Zostera. Living speci- 

 mens of these species are not now within my reach or further 

 details might be given, and sketches. The same thing happens in 

 a. Scyllaeid*, the brilliant green and the brown forms of which are 

 found near together in Chnaka Bay, Zanzibar, whilst greenisli to 

 deep brown varieties occur here (Dongonab) in the Red Seat The 

 other point about the coloration of these forms (Scyllaeid and 

 Tectibranchs) is the occurrence in so many species of small brilliant 

 blue spots, sometimes linged with yellow, the oidy conspicuous 

 thing about otherwise scarcely visible creatures. These may be 

 " recognition marks " but are more likely to be glands +. 



We have then an excellent ca,se for the theory that the brilliant 

 colour of these a,nimals has a protective value. They walk abroad 

 where others must creep and hide. 



Distastefulness was proved by trying to feed fish with specimens 

 (mostly C. reticulata^ twice with C. diardii) thrown from the 

 windows of my houseboat. The kitchen refuse, and the shelter 

 afforded from the suii had made the surrounding water populous 

 with fish, and on a calm morning every detail of their movements 

 was clear. The water was shallow, the bottom sandy, with a 

 covering of short "sea grass," the usual habitat of sevei-al fish and 

 often of considerable numbers of Chromodoris reticidata, more 

 rarely of C. diardii. 



The Garfish, Belone sp., is the only one of these animals with a 

 specialised diet. It is ever on the watch floating near the surface, 

 herding together the shoals of " sardines " [Engraulis ? boelama), 



* Crosslandia wrHis Eliot, P. Z. S. 1903, pp. 61-68 ; C. fusca Eliot, Jouni. Liuii. 

 Soc, Zool. xxxi. 1908, p. 90. 



t The n:reen Zaiiziliar speciinen was fouiul on Zostera, wliich is less abundant in 

 tlie R'^d Sea and from wliich I hnve not yet obtained thi;* species. 



X Other brilliantly coloured Nudibranch families are the Polyceridte and Aeolidse. 

 Of the former I have seen too few specimens to generalise, bvit one of the most beau- 

 tiful, the wine-red Flocamoplierus ocellatus, was merely a lig'hter tint of the colour 

 of its environment, a deep red polyzoan on wliich it fed. There is some evidence that 

 it owes part of its colour to its foodstuff.i Another, Treveleyana crncea '^, is a little 

 slugr-shaped beast of a brilliant yellow colour. It periodically occurred in great 

 swarms in Chuaka Bay, Zanzibar, in the open, not hiding in any way. The Aeolids 

 are all bright coloured, I believe, and all, or nearly all, gain protection by living 

 amongst hydroid zoophytes, and even can utilise the stinging-thread cells of the 

 latter in their own bodies. 



Tritonids often live among zoophytes, in Zanzibar often among fleshy Alcyonaria, 

 and are fairly conspicuously coloured. But Meli.be fimhr lata , a large animal, in colour 

 and in the shape of its cerata and the processes it bears, looks extremely like a 

 fragment of drifting fucus-weed. 



1 E'.iot, Sir C, " Marine Biology of the Sudanese Red Sea," Journ. Linn. Soc. 

 xxxi. Nov. 1908, p. 104. 



2 Eliot, Sir C, "Nudibranclis from East Africa and Zanzibar," P. Z. S. 1904., vol. ii. 

 p. 87. 



