Rhabdocalyptus dawsoni

Rhabdocalyptus dawsoni (Lambe, 1893)

(Fig. 6B)

Limited Synonymy:

Bathydorus dawsoni Lambe, 1893, 73;

Rhabdocalyptus dawsoni Ijima, 1898, 54; Schulze, 1899, 54; Koltun, 1967, 103; Leys & Lauzon, 1998, 111;

Rhabdocalyptus dawsoni dawsoni, Koltun, 1967, 103; Reiswig, 2018, 126.

Acanthascus dawsoni, Dohrmann et al., 2012, 12.

Acanthascus (Rhabdocalyptus) dawsoni, Tabachnick, 2002, 1451; Dohrmann et al., 2012, 12.

Material examined. CAS 223595, col. no. NA085-052-A, E/ V Nautilus w ROVs Hercules & Argus, Cordell Bank, Calif., 38.11ºN, 123.66ºW. 2112.7 m, 09 Aug. 2017.

Comparative material. Lectotype of Rhabdocalyptus dawsoni, here designated, NMC 1900-7061, col. G.M. Dawson, 1855. off mouth of Qualicum River, Vancouver Island, British Columbia, Canada, figured L. Lambe, 1893, Pl. IV, fig. 2.

Description. The specimen was pendant from an attachment site on a steep wall as recorded in the frame grab of the collection video (Fig. 6B). The body was cylindrical, 26.3 cm long by 6.3 cm in diameter with sharply tapered ends. It was entirely covered by sediment and epifaua adherent to smooth prostal diactins and both smooth and thorned hypodermal pentactins. The distal half of the specimen was collected.

Spicules of the specimen are fairly consistent with those of the lectotype of Rhabdocalyptus dawsoni, for example, tangential rays of hypodermalia are 1.0– 2.9 –5.5 (n = 18) mm here vs 0.9– 2.6 –4.1 (n = 35) mm in the lectotype and discoctaster diameter is 77- 103 -125 (n = 111) µm here vs 54– 66 –86 (n = 50) in the lectotype. Intact microdiscohexasters could not be found in the Cordell Bank specimen but small hexactine centers without terminal rays may be the remnants of them. In view of the agreements in spicules such as dermalia, atrialia and microscleres, it seems certain that the specimen belongs to the widespread species R. dawsoni.

Distribution. The species Rhabdocalyptus dawsoni has a known distribution from southern California to Cape Spencer, Alaska and probably into the Bering Sea at depths of 10 to 437 m. The Cordell Bank specimen was collected well within the known geographic range but at 2112.7 m it is a major depth extension for the species.