Phoronids are a small phylum of marine invertebrates consisting of only 15 species, most of which have a worldwide distribution. In the majority of marine ecosystems, phoronids are the dominant species, forming high-density aggregations and thus playing an important edificatory role.

The external morphology of phoronids is poor, and for an exact identification of the species it is necessary to obtain a complete series of histological sections and construct a three-dimensional reconstruction of some internal of its organs. If such morphological work is carried out, it becomes clear that most phoronid samples from previously unexplored water areas are new species. Another problem in phoronid taxonomy is the synonymization of species, which in many cases is very controversial. One important issue in phoronid taxonomy is the description of species by their larval stages—actinotrochs. More than 50 so-called "larval species" have been described, which indicates the existence of undescribed species of adult phoronids.

The present work is devoted to the anatomy and phylogenetic analysis of two populations of Phoronopsis harmeri: from Vostok Bay, the Sea of ​​Japan, and from Friday Harbor, on the Pacific coast of North America. Morphological studies made it possible to describe in detail the structure of organ systems important for species identification, such as the lophophore's shape, the structure and number of longitudinal muscle bands, the structure of giant nerve fibers, and the shape of metanephridia. For molecular genetic analysis, we studied the sequences of the 28S rRNA and COX1 genes obtained by us from Phoronopsis harmeri / viridis samples from the indicated locations, as well as those taken from the GenBank and belonging to individuals of these two species from different waters of the World Ocean. The obtained data allow us to raise the question of the possible revalidation of the species Phoronopsis viridis.