This study examines the taxonomic structure and commonality of species composition ascidians in Arctic seas Russia, where there are currently registered more than 70 representatives this group. Quantitative analysis taxa different ranks inhabiting area demonstrates that their abundance decreases from west to east, all seas, except Kara Sea, is understudied on average by 13±4%, understudy increa...

Adult Boltenia villosa (phylum, Chordata; subphylum, Urochorda [Tunicata]; class, Ascidiacea) were collected intertidally. Gametes and embryos were handled according to standard procedures (Fernald, 1959; Costello et al., 1957). Living embryos in gastrula or neurula stages were pipetted into the fixative accompanied by a small amount of seawater. The fixative was either (a) 2.7% Os04 in approxi...