ИСТИНА

Holasteroid sea urchins are presented by the exclusively deep-sea species classified into the order Holasteroida consisting of 7 families with 20 mainly monotypic genera. Most numerous in the number of species are families Pourtalesiidae and Urechinidae. By morphology data, pourtalesiid holasteroids are splitted into three parallel evolutionary lineages that differ in plastron plating. The different evolutionary lineages can be traced for the other major family, Urechinidae. Molecular-based phylogeny (fragments of COI and 16S rRNA genes and nearly complete 12S rRNA gene) supports morphology-based evolutionary trends for both Pourtalesiidae and Urechinidae (Fig. 1). Morphologically primitive species from families Carnarechinidae and Stegasteridae occupy the basal place at molecular tree; Urechinidae and Pourtalesiidae species split up into evolutionary lineages corresponding morphological ones with primitive species at their base and advanced forms at the crown. Analysis of morphological and molecular data as well as geographical distribution suggests that main center of pourtalesiid and urechind dispersal is abyssal Antarctic. Less specialized pourtalesiids and urechinids have penetrated only East and North Pacific. More specialized ones are distributed throughout the abyssal of the world ocean; they also have emerged into bathyal zone.