Acanthascus ( Rhabdocalyptus ) borealis Okada, 1932

Acanthascus ( Rhabdocalyptus) borealis Okada, 1932 View in CoL

Fig. 5 View Fig ; Suppl. Tab. 3.

MATERIAL. IORAS 5 /2/3827: RV ‘ Akademik M.A. Lavrentyev’ – 75, ROV ‘ Comanche’, sta. 18, spec. 3-1, 55.4382° N 167.2652° E, 1569 m GoogleMaps . IORAS 5 /2/3808; 3814: RV ‘ Akademik M.A. Lavrentyev’ – 75, ROV ‘ Comanche’, sta. 9, spec. 2-5 and 2-2 correspondingly, 55°28′58.8″ N 167°15′30.6″ E, 2849 m GoogleMaps .

DESCRIPTION. BODY. The biggest specimen is IORAS 5/2/3827: 160 mm high, 60 mm in maximal diameter (close to the osculum); walls are 2–6 mm thick. Prostalia oscularia are diactins which protrude up to 20 mm over the osculum, prostalia lateralia are hypodermal pentactins which make a dense cover up to 15 mm above the dermal surface. Other specimens are smaller: IORAS 5/2/3814: 60 mm high, 20 mm in diameter in the middle and 15 mm in diameter of the osculum, the walls are 1–1.5 mm thick; IORAS 5/2/3808: 50 mm high, 25 mm in diameter in the middle and 20 mm in diameter of the osculum, the walls are 2–3 mm thick. Prostalia in the small specimens is smaller: oscularia diactins protrude up to 15–20 mm, prostalia lateralia of hypodermal pentactins (their tangential rays) are 10–15 mm over the dermal surface. The hypodermal pentactins are most parathropal with spiny tangential rays.

REMARKS. Differences between the new and previousely described specimens of A. ( Rhabdocalyptus) borealis ( Okada, 1932; Koltun, 1967) are given in the Suppl. Tab. 3. The most important of them: no microdiscohexasters in all investigated specimens were observed; smaller diameter of the oxyoidal microscleres; the ray of atrial hexactin may be notably smaller. Nevertheless these features are considered to be intraspecific, they are widening the species limits. Morever, the specimen described by Koltun (1967) has some additional intermediate parameters.

DISTRIBUTION. Bering Sea, Pacific side of Kuril Islands, at 440–2849 m depth.