Principles of main body components and phylogenetic relations of phyla in coelomate animals. 1. Main body components, evolution of organization of coeloms and phylogeny of Deuterostomia

摘要

The principles of main body components and the concept of evolutionary levels of organizing the coelom are discussed. These concepts are shown to restrict hypotheses of phylogenetic relations of the coelomate phyla. Myzostomida and Dinophilida are recognized to be lowest coelomates. The division of coelomates into two main phylogenetic branches (macrotaxa), Protostomia and Deuterostomia, has been accomplished at the proarchicoelomatic level, characteristic of Mollusca and Testicardines. The further evolution of coelomatic formations proceeded independently of these two branches. The transition to the archiloelomatic level was realized by growing the metacoel (which often becomes the main body cavity) and the corresponding body part. This fact could be observed even in taxonomically related groups (e.g. Testicardines and Crania). The hypothesis of dividing coelomates into Protostomia and Deuterostomia permits one to supplement identification of these mcrotaxa with five pairs of parameters (coelom formation, larva types, paired and unpaired arcocoels of the first coeloms, presence or absence of coelomoducts, degree of developing ventro-postanal continuation of the body, and shape of somites in segmented forms). Accepting that the lowest Deuterostomia are brachiopods (excluding Pleuropygia) or Testicardines, being at the proarchicoelomatic level, such deuterostomian groups and Graptolitha (including Pterobranchia) and Echinodermata, being at the same level, can be revealed as well as protomocoelomate-segmented Enteropneusta which lost sgementation, Vestimentifera with segments in the opisthosome, Tunicata, and Chordata. An essential feature of the structure in the last type implies that its representatives turn the body over and move with neural side upward that is also proved by genetic studies.