XII 



NEREIDIFORMIA 



309 



are biramous. 0. vittatus Sars is dredged in numbers off the 

 Scotch coast, and is found also at low tides. It measures 2 

 inches in length. A closely allied species lives in the ambulacral 

 grooves of the starfish Astropecten. 



Fam. 3. Aphroditidae? The most characteristic feature of 

 this family, and one by which its members are absolutely distin- 

 guished from all other Chaetopods, is the possession of scales or 

 " elytra " on the back. These flattened dorsal cirri are of a some- 

 what horny texture, and are carried, generally, on alternate 

 segments of the body ; filamentous cirri occurring on the other 

 segments. In the sub-families Hermionina and Polynoina the 

 elytriferous segments are 2, 4, 5, 7, 9, etc., up 

 to 23 ; then every third segment. The 

 worms are usually short, with some thirty- 

 five to forty-five segments, though Sthenelais 

 and a few others have many more. (For head 

 see p. 262, and for parapodium see pp. 265, 

 268.) The pharynx is very thick walled, and 

 furnished with two pairs of jaws, which are, 

 however, not hardened in the sub-family 

 JFfi-mionina. The intestine is provided with 

 a number of paired longer or shorter caeca 

 (Fig. 142). A considerable number of this 

 family are commensal or parasitic (see p. 

 297). The famijy J is well represented on 

 our own coasts, so that only a few of the 

 more readily distinguishable species can be 

 here described. 



Sub-Fam. 1. Polynoina. Body flattened, 

 with nearly parallel sides, usually short, 

 more rarely worm-like ; three tentacles ; peristomium with long 

 dorsal and ventral cirri ; the ventral cirri of the next segment 

 are also elongated. Jaws are present. Elytra, visually twelve 

 to eighteen pairs, the surface of which is more or less papillose, 

 and may be " fringed " along the outer border, with long processes. 

 The colouring of the elytra is characteristic in most cases, though 

 liable to considerable variation in some species. The chaetae 

 are generally strong, and of bright golden colour: they are ;ill 

 unjointed. The Polynoina are generally but feeble swimmers, 



1 See M'Intosh's Memoirs, loc. cit. 



Fig. 161. Polynoe squa- 

 mata L. Nat. size, c, 

 Notopodial cirrus ; e, 

 elytron ;/, parapodium ; 

 p, palp ; t, tentacle. 

 (From Johnston.) 



