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This work studies a new genus Apseudocnus and three new holothurian species: Apseudocnus albus, Cucumaria obscura, and C. fusiformis, found in samplings of the 27th and 29th cruises of the research vessel Akademik Oparin to western and southeastern areas of the Okhotsk Sea. The new species distinctly differs from other known cucumariids in the structure of spicules of the body walls, tentacles, and the circumpharyngeal calcareous ring. Descriptions of the new taxa are presented with diagnoses and figures.

The genital papilla structure of female and male specimens is studied in four species of large holothurians of the genus Cucumaria from the Far Eastern seas of Russia: Cucumaria japonica (Semper), C. okhotensis Levin et Stepanov, C. anivaensis Levin, C. djakonovi Baranova. The papillary forms in these species are extremely various and cannot be considered as characteristic for the species.

Cucumaria anivaensis sp. nov. is described from Aniva Bay (Sakhalin). This species is characterized by having large lengthened plates in the body skin with large apertures in the medial region and small apertures at both edges, very long plates with an outgrowth on one side in the tentacles, and an expanded basis of the radial plates of the pharyngeal ring. Some plates of the oral disk have strong enlargement in the medial region.

This paper presents a description of Cucumaria okhotensis sp. nov. from the shelf of western Kamchatka. The new species is characterized by large elongated plates on the dorsal side of the body that have radiating holes on one side of the spicule; a light coloration of tentacles; and, in adult animals, extended sclerites on the processes interconnecting the radial and interradial plates of the circumpharyngeal calcareous ring.

A description of Cucumaria conicospermium sp. n. is given. It differs from other species of the genus Cucumaria by the shape of spicules on the body skin and by the introvert, as well as sperm, morphology.