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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 2383

Y. Shirayama and W.D. Hope; Cephalic Tubercles, A New Character Useful for the Taxonomy of Desmoscolecidae (Nematoda). Trans.Amer.Micros.Soc. 111(3):211-222, 1992

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The cephalic regions of 10 nematode species of the family Desmoscolecidae were examined by scanning electron microscopy (SEM). They belonged to two genera, Tricoma and Desmoscolex, which were collected from off the coasts of Japan, Caribbean Sea, Clew Bay (Ireland), and Thailand. The basic structure of the lip region was the same within Tricoma regardless of geographic region, but a distinct intergeneric difference was found. In species of this genus, six conspicuous outer labial sensilla protruded from the smooth lip surface, and the circular ridges corresponding to the boundary of the closed oral aperture, the external rim of the labia, and the anterior rim of the cephalic concretion ring were distinctive. On the other hand, the labial surface of specimens of the genus Desmoscolex was covered by a variety of small, tuberculate structures. These cephalic tubercles were 70-240 nm in diameter and recognizable only by SEM examination. The shape of the cephalic tubercles and the area of the head covered by them were constant within the same species, but differed among species. The labial sensilla were surrounded and obscured by specialized cephalic tubercles in Desmoscolex. The cephalic tubercles were found only in adults of Desmoscolex. These results suggested that the presence of cephalic tubercles is a synapomorphic character of Desmoscolex, and that it is useful for phylogenetic studies of the Desmoscolecidae.