NAKED-GILLED SUBGROUP 



3325 



The family Polyceridce is distinguished from the Dorididce by having non- 

 retractile gills; the principal genera being Goniodoris, Acanthodoris , Idalia, Ancula, 

 Polycera, Plocamophorus , Triopa, and sEgirus. Ancula cristata is an elegant little 

 creature, about half an inch in length, occurring upon most of the British coasts. 

 It is white, with the processes tipped with yellow or orange. The tentacles are 

 laminated and nonretractile, each having two styliform appendages at the base. 

 The gills are placed in the middle of the back, on each side of which there are a few 

 compressed appendages. 



This division of Nudibranchs was established for a group of naked 



marine mollusks having the gills placed symmetrically along each 



side of the body between the margin of the dorsal mantle and the 



edge of the creeping disc. Phyllidia and Pleurophyllidia are the typical genera 



originally described, and may be regarded as the principal representatives of this 



Ancula cristata (much enlarged). 



group of mollusks. One group of Inferobranchs, however, is abnormal in being 

 destitute of external branchiae. In the genus Phyllidia, containing several very 

 handsome species, the animal is somewhat depressed, and covered with a leathery 

 and sometimes tuberculated mantle; the head is small and concealed between the 

 foot and back; and the two oral tentacles are short, the dorsal pair retractile into 

 cavities toward the anterior end of the body as in Doris. The laminated gills 

 extend the entire length on both sides. The vent is dorsal and at the posterior 

 part of the mantle, and the reproductive organs are on the right side. In the dis- 

 position of the branchiae these animals are very like the chitons and limpets. They 

 are remarkable for possessing neither jaws nor radula, the mouth being modified 

 into a sucker, as in the Doridopsidce : These animals are so apathetic that they 

 have never been observed to make any movement, but appear as if dead. They are 

 inhabitants of tropical seas, the few species that are known occurring in the Red 

 Sea and the Indian and Pacific Oceans. In the allied Pleurophyllidia the animals 



