Dumetocrinus antarcticus Bather 1908

Dumetocrinus aff. antarcticus (Bather, 1908)

Figure 3.

Synonymy: Dumetocrinus antarcticus Gutt et al., 2011: 6, fig. 4D.

Material examined. Holotype (spec. B) and two paratypes (spec. A, C), IRSNB 1897/1999-10131-589; paratype (spec. D) NHM 1937-4-29-1: Belgica Expedition, Faubert 11, sta. 589, W of Antarctic Peninsula, 70°23’S – 82°47’W, 480 m, 1898. R/V Polarstern cruise ANT XXIII/8, station PS69/710-5 Larsen area, E of Antarctic Peninsula, 65° 32.94’ S – 61° 38.59’ W, depth 242 m, 2007 (1 specimen with distalmost stalk missing).

Description. Specimen almost complete except for the distalmost stalk (Fig. 3 A–B); length of preserved stalk 10.0 cm with proximalmost diameter 1.9 mm; height of aboral cup 6.3 mm with diameter at top of radial ring 6.9 mm; ratio of radial upper width to primibrachial width 2.0 to 2.2; arm length about 36 mm; maximum pinnule length 16 mm. Dorsal cup and tegmen smooth and brachials without lateral wings. Relatively gracile arms with up to 20 well-differentiated pinnules on each side; first pinnule always on Br4. Arm pattern 1+2 3 4 5+6 7 8+9 10 11 12 13 (3 cases), one arm broken at Br20 after 12 successive muscular articulations, the single complete arm with brachial pairs at 17+18 and 28+25. Tegmen moderately inflated with anal cone lower than oral cone and conspicuous concave orals (Fig. 3 C). Pinnules without genital inflation and lateral plates, very sharp triangular cover plates as described by John (1937: fig. 2). Proximal columnals articulated by symplexies with 8 crenular units of 1 crenula (Fig. 3 D), distal syzygies with radial crenularium of relatively wide crenulae (Fig. 3 E).

Remarks. This specimen differs from specimens of the type-series of D. antarcticus mainly in lacking thecal ornamentation (see John 1937, fig.1), adoral inflation of arms and pinnules, H-shaped plates and lateral plates in pinnules (see Mironov & Sorokina 1998a, fig. 5), and by fewer number of crenular units in symplexies than described by Roux (1980b). However, the arm pattern, typically sharp cover plates, tegmen characters and general pattern of stalk articulation (see for comparison Fig. 3 E and 3F) suggest very close affinities with D. antarcticus. In the genus Ptilocrinus, two closely related species also differ mainly in the presence versus absence of proximal inflation and lateral plates in pinnules (Roux & Lambert 2011). The absence of genital inflation in pinnules may also be a juvenile trait. However, both this specimen and those in the type series of D. antarcticus are of similar sizes. If this specimen without inflated genital pinnules is a juvenile, adults would be much larger than in D. antarcticus. It was also collected in shallower water than the latter species. Because a new species should not be described from a juvenile specimen, additional specimens are required to determine whether or not it is distinct from D. antarcticus.

Occurrence. East of the Antarctic Peninsula (Larsen area). Data from photographic survey (Gutt et al. 2011) document a depth ranging from 193 to 449 m (Julian Gutt and Stephanie Langner, personal communication), the shallowest record for any Hyocrinidae.