A number of embryological features of the Pogonophora suggest that they could not derive from the Polychaeta and are closely related to Deuterostomia. These are: (1) traces of spiral cleavage that sharply differ the from cleavage of polychaetes in the prospective value of blastomeres; (2) enterocoelic formation of mesoderm; (3) the larva most closely resembles Balanoglossus that has just completed metamorphosis; proto-, meso-, and metasoma of pogonophoran larva correspond (or are homologous) to the proboscis, collar, and trunk of Balanoglossus respectively; while the telosoma can be regarded as an organ appearing late in phylogenesis that serves to burrow into the bottom; (4) larvae of Siboglinum have a transitory mouth located, as it is the case in Enteropneusta, between proto-and mesosoma, very far from the posterior end, where there is closed blastopore; therefore, the former can be considered as a secondary mouth; (5) the asymmetrical development of the anterior pair of coeloms in Pogonophora, Echinodermata, and Amphioxus allows finding homologies between organs developing from these coeloms.
Russian Journal of Marine Biology – Springer Journals
Published: Nov 16, 2007
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