Principle of main body components and phylogenetic relations of phyla in coelomate animals. 2. levels of organization of coeloms and phylogeny of protostomia

摘要

The principle of main body components and the concepts of evolutionary levels of coelomic formations are used in elaboration of coelomate phylogeny. Molluscs are at the proarchicoelomate level. They have small metacoel (pericardium) and larger mesocoel (commonly used as gonocoel); acrocoel (the 1st coelom) is absent and it is likely primary. Sipunculida (the sole phylum of Protostomia with developed ventro-postanal continuation of the body) and Tentaculata (=Podaxonia) are also at archicoelomate level. The latter also includes the group Pleuropygia (i.e. "brachiopods" with chitinous-phosphatic shells), the representative of which are similar to phoronids by the presence of ventral projection of the body. The protomocoelomate level is characteristic of the annelids without a growth zone (for instance, Hirudinea) as well as of Echiurida and Pogonophora. However, it is difficult to separate annelids of this level from the others due to the absence of data on growth zones. Pogonophora belongs to prostomes due to some species have larvae of trochopore type and specific features of opisthosomal somites. The recent data permitted one to attribute Nemertini to the same group, because their rhynchocoel, gonads, and lateral "blood vessels" are coelomic formations, and plurality of gonads and gonoducts testifies to segmentation of their ancestors. The tomocoelomatic level is characteristic of the part of Annelida and Arthropoda lost or having growth zone. A list of 8 holapomorphic parameters for arthropods indicating a monophyly of this phylum. A phylogenetic scheme is give.