378 CHJETOPODA. 



anterior end of the body (Gephqlotrocha, 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., Spio-Nephthys- 

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

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

 ventrally and dorsally (Am/phitrocha). In other cases one or more 

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

 terminal rings (pra?oral and perianal) are absent (Telepsavus-Chcetop- 

 terus larva] (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 Chsetopod 

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

 the larva of Loven. 



Relatively few forms, as for instance the transparent Alciopidce, 



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- 

 tenna? and appendages. The elytra of 

 Polynoc, the tentacles of Poly cirrus, and 

 the integument of certain Syllidce, are 

 also phosphorescent. Panceri* has shown 



FIG. 307. Nereis murgaritacea. 



Head with protruded jaw that the seat of the phosphorescence is 

 apparatus of the pharynx, unicellular cutaneous glands, which, in 



from the dorsal surface (after 



M. Edwards), z, Jaws; F, Polynoe, were proved to be in comniuni- 



^r^ 1 ^"'^ cation with nerves. 



Sub-order 1. Errantia. Free-swim- 

 ming, predacious Polychceta. The prsestomium 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 Tubicolcc, and, 

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

 anterior portion of the pharynx can be protruded as a proboscis 

 and is divided into several portions ; it \s either beset with papillae 

 or contains a powerful masticatory appaVatiis, which appears at its 

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

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



* Pauceri, "L*luce e gli organi luminosi cli alcimi annelidi," Atti della E. 

 Acad. sciensz ii. e mat. di Napoli, 1875. 



