BASEODISCUS PROFUNDUS SP. NOV.

(FIG. 2G)

Baseodiscinae sp. 21DS: Chernyhsev & Polyakova, 2018: 125, 128, 130, table 1, fig. 1F, fig. 4B.

Baseodiscinae sp. 7DS: Cheryshev & Polyakova, 2018: 125, table 1.

Zoobank registration: u r n: l s i d: z o o b a n k. o r g: a c t: C 8 9 2 A 8 8 C - D E B F - 4 4 A 5 - A D 1 C - 0DE7D9823B69.

Material examined: Two specimens, collected by A. V. Chernyshev. Holotype, MIMB 42257, 22 July 2015, S/ V Akademik M.A. Lavrentyev, station 7-1, Sea of Okhotsk (46°57.0′N, 151°05.0′E), 3300 m depth, mud. Paratype, MIMB 42258, 23 July 2015, S/ V Akademik M. A. Lavrentyev, station 7-11, Sea of Okhotsk (46°57.0′N, 151°00.4′E), 3306 m depth, mud .

Sequences: Determined by Chernyshev & Polyakova (2018). From the holotype (as Baseodiscinae sp. 21DS): MF512047, 16S (499 bp); MF512072, 18S (1760 bp); MF512098, 28S (359bp); MF512140, H3 (331bp). From the paratype (as Baseodiscinae sp. 7DS): MF512045, 16S (499 bp); MF512070, 18S (1770 bp); MF512096, 28S (1050 bp); MF512138, H3 (331 bp) .

Etymology: The new specific name is the Latin adjective profundus meaning ‘deep’.

Description: Body 25–27 mm long, 1.0–1.2 mm wide, cylindrical in foregut region and slightly flattened in region of intestine; head dark rose, body pale rose, yellowish gonads visible through integument (Fig. 2G); thin transverse furrows present; secondary furrows not confirmed; eyes absent; mouth small, pit-like. Diagonal muscle layer absent in proboscis (Chernyshev & Polyakova, 2018).

Distribution: Known only from the Sea of Okhotsk (Chernyshev & Polyakova, 2018).

Remarks: This new species differs from other species in the genus in having a relatively small, narrow body lacking any specific colour patterning. Baseodiscus profundus may be unique within the genus in lacking the proboscis inner diagonal musculature, which has been confirmed in all the other congeners studied so far (Magarlamov & Chernyshev, 2011; Chernyshev, 2015).