. Elementary text-book of zoology. Zoology. 378 CHJETOPODA. anterior end of the body (Gephqlotrocha, , larva of Polynoe). Sometimes there are two rows, one at each end of the body, con- stituting a prseoral and perianal ring (Telotrocha, , 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-Chcet
. Elementary text-book of zoology. Zoology. 378 CHJETOPODA. anterior end of the body (Gephqlotrocha, , larva of Polynoe). Sometimes there are two rows, one at each end of the body, con- stituting a prseoral and perianal ring (Telotrocha, , 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?, s
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1884
