ИСТИНА

The phylum Brachiopoda is a relict group of marine invertebrates known from lower Cambrian Deposits. Their position in the animal system remains controversial, with morphological data often being inconsistent with the results of molecular phylogenetic analysis. According to classical concepts, brachiopods were divided into two classes: Articulata (Testicardines) with a hinge between the dorsal and ventral valves and Inarticulata (Ecardines), which have no hinge. We studied the structure of the sperm and the nucleotide sequences of the 18S and 28S rRNA genes in the articulate brachiopods Coptothyris adamsi and analyzed on this basis the macro-phylogeny and classification of modern brachiopods. Phylogenetic trees of the combined sequences of 18S and 28S rRNA genes were built by Bayesian analysis using MrBayes version 3.2, as well as by the method of maximum likelihood using RAxML v. 7.4.2 with a raxmlGUI v. 1.3 graphical interface. The spermatozoa of C. adamsi are similar to those of other articulate brachiopods. Two types of sperm structure can be distinguished within Brachiopoda: the first type is characteristic of the articulate brachiopods (Rhynchonelliformea), the second type, the inarticulate brachiopods (Linguliformea and Craniiformea). Rhynchonelliformea spermatozoa are similar to those of the deuterostome animals, in particular to the sperm of the Echinodermata, whereas Linguliformea and Craniiformea spermatozoa are similar to the typical sperm of the Trochozoa, such as annelids and mollusks. The two types of sperm structure suggest great differences between the inarticulate and articulate brachiopods. Perhaps this is the result of an ancient origin of brachiopods, whose ancestors were probably close to the group of animals that are ancestral to protostome and deuterostome animals. Our tree of the combined sequences of the 18S and 28S rRNA genes, as well as the trees that are based on a great number of genes from the representative taxonomic sample show that brachiopods and phoronids form monophyletic groups that join together in grouping Brachiozoa, with phoronids occupying the basal position and brachiopods dividing into two groups corresponding to the articulate (Rhynchonelliformea) and inarticulate (Linguliformea and Craniiformea) species. Thus our results of the molecular phylogenetic analysis and the structure of the spermatozoa support the division of Brachiopoda into two groups, viz., Inarticulata (with the classes Linguliformea and Craniiformea) and Articulata (with the class Rhynchonelliformea); this corresponds to the traditional notion on the systematic position of brachiopods.