Observations on Development and Metamorphosis of Siphonosoma Cumanense with Comparative Remarks on Sipunculus Nudus (Sipuncula, Sipunculidae)
Abstract:The development of Siphonosoma cumanense (Sipuncula, Sipunculidae) is described from fertilization through trochophore and planktotrophic pelagosphera larval stages and metamorphosis of the pelagosphera to the juvenile. The planktotrophic pelagosphera larva becomes competent to metamorphose at 8 weeks of age, at which time metamorphosis can be induced by exposure to sediment previously occupied by adults of this species. The resemblance of this pelagosphera larva, reared in the laboratory from known adults, to that of an oceanic larva frequently collected in the Gulf Stream System, confirms the previously tentative identification of the oceanic larva as Siphonosoma cumanense. This is the first study in which a sipunculan species known to possess a planktotrophic oceanic larva has been reared in the laboratory from fertilized egg to juvenile. Comparisons of the development of Siphonosoma cumanense and Sipunculus nudus, both in the family Sipunculidae, show marked differences. Whereas in S. cumanense the developmental features are similar to those of species in other families of the Sipuncula which have planktotrophic development, in S. nudus the embryo differs in that it is enclosed by ciliated cells which are presumed homologues to the prototroch cells of other species, and, at transformation to the pelagosphera, it casts off these cells as well as the entire overlying egg envelope. It is concluded that the peculiar developmental features of S. nudus are not characteristic of the family Sipunculidae and can be considered as highly modified within the phylum.
Document Type: Research Article
Publication date: January 1, 1988
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