ИСТИНА

Echinidae is the family of sea urchins, widely distributed across the World Ocean, mostly at bathyal depths. It comprises 5 genera and 25 species. Molecular phylogeny of the family was studied using the COI, 16SrRNA and 12SrRNA mitochondrial gene sequences obtained for 16 species representing all 5 genera. The resulting tree consists of two major well-supported clades, one including species of Sterechinus and Dermechinus and the second one including species of Echinus, Gracilechinus and Polyechinus. Species of the second clade are arranged in distinct phylogenetic lineages do not supporting the validity of the three latter genera. Genera from the two clades differ in geographic distribution. Sterechinus and Dermechinus are confined to the Southern Hemisphere, with most of species distributed in the Antarctic and Subantarctic. The center of species richness of these genera lies in the Scotia Arc region (5 of 6 species). The group of Echinus, Gracilechinus and Polyechinus is distributed across all oceans except the Antarctic, with the center of species richness in the North-East Atlantic (7 of 18 species). The most reliable fossil records of echinid sea urchins are presumably shallow-water species known since late Miocene from the Mediterranean and the adjacent part of Atlantic. Combination of data on fossil records, extant species distribution and molecular phylogeny suggest a scenario of dispersal for the family Echinidae. This scenario includes three main stages. First, separation of “northern” and “southern” groups of shallow-water echinids in the Atlantic Ocean. Second, colonization of the deep-sea at moderate latitudes in the North and South Atlantic by echinids of the “northern” and “southern” groups respectively. Third, dispersal to other regions at bathyal depths. Echinids of the “northern” group penetrated the South-East Atlantic and Indian Ocean, and later dispersed to the Pacific. Recent study on the evolutionary history of the genus Strerechinus (Diaz et al., 2011) revealed dispersal from the subantarctic Atlantic across Antarctic and Subantarctic bathyal.