378 



CH.ETOPODA. 



anterior end of the body (Ccf)halotrocJia, e.g., larva of Polynoe). 

 Sometimes there are two rows, one at each end of the body, con- 

 stituting a prseoral and perianal ring (Telotrocha, e.g., Sjjio-Nephtliys- 

 larvct). In addition to these two rings of cilia, incomplete rings 

 may also be present on the ventral surface (Gastrotroclia), or both 

 ventrally and dorsally (AmpMtrochoi). In other cases one or more 

 rows of cilia surround the middle of the body (Mesotrocha), while the 

 terminal rings (prjeoral and perianal) are absent (Telepsavus-Chcetop- 

 terus larvci) (fig. 306). Many larvae are provided with long pro- 

 visional seta?, which are later replaced by the permanent structures 

 (Metachceta). In spite of their great diversity of form the Chaetopod 

 larvae can in their later development also be reduced to the type of 

 the larva of Loven. 



Relatively few forms, as for instance the transparent Alciopidcr, 



live at the surface (pelagic animals) ; most 

 of them live near the coast. Numerous 

 forms descend into the deep sea. Many 

 have the power of emitting an intense 

 light, especially species of the genus Chce- 

 topterus which emit light from their an- 

 tennse and appendages. The elytra of 

 Polynoe, the tentacles of Polycirrus, and 

 the integument of certain Syllidce, are 

 also phosphorescent. Panceri* has shown 

 that the seat of the phosphorescence is 

 in unicellular cutaneous glands, which, in 

 Polynoe, were proved to be in communi- 

 cation with nerves. 



Sub-order 1. Errantia. Free-swim- 

 ming, predacious Polycha'ta. The pnestorniuni always remains in- 

 dependent and forms, with the oral segment, a well-marked head 

 which bears eyes, tentacles, and usually tentacular cirri. The 

 parapodia are much more developed than in the Tubicolce, and, 

 together with their very variously shaped setae, serve as oars. The 

 anterior portion of the pharynx can be protruded as a proboscis 

 and is divided into several portions ; it is either beset with papilla; 

 or contains a powerful masticatory apparatus, which appears at its 

 extremity when protruded (fig. 307). Branchice may be wanting; 

 when present, they usually appear as comb -shaped or dendritic 



FIG. 307. Nereii margaritucea. 

 Head with protruded jaw 

 apparatus of the phnrynx, 

 from the dorsal surface (after 

 M. Edwards). E, Jaws; F, 

 tentacles ; P, palps ; Fc, ten- 

 tacular cirri. 



* Panceri, " La luce c gli organ! luminosi di alcuni annelidi," Atti dclki E. 

 Acacl. sciensz fi. e mat. di Napoli, 1875. 



