Ophiura ljungmani

Ophiura ljungmani (Lyman, 1878)

EAST ATLANTIC OCEAN • 1 specimen; off Ghana, Takoradi; 04°00’N, 001°43’W; 1445; 20 Nov. 1950; Galathea II stn. 33; grey clay; NHMD-868674 • 3 specimens; off Gabon; 02°00’N, 009°14’E; 1500–1520 m; 02 Dec. 1950; Galathea II stn. 63; blue clay; NHMD-305711.

NORTH ATLANTIC OCEAN • 1 specimen; off Iceland; 64°54,34’N, 029°58,39’W; 2005–2007 m; 25 Aug. 1996; BIOICE stn. 2914; SMNH-41981, SMNH-41982 • 1 specimen; off Iceland; 62 51,49°N, 014 41,65°W; 1729 m; 11 July 1997; BIOICE stn. 3067; SMNH-87642.

Remarks

This species strongly resembles the Atlantic Ophiura ljungman i (Lyman, 1878). They differ in the shape of the dorsal arm plates, which in O. spinicantha (Fig. 2A–E) are rectangular, proximally wider than long, but soon becoming longer than wide, with a notch in their distal edge, and hexagonal, with straight edges, at the distal end with slanted sides in O. ljungmani (Fig. 2F). The disc scalation is finer in O. spinicantha than in O. ljungmani and the oral shield is somewhat larger in proportion (Figs 2E; H). Both species usually have three arm spines (occasionally four), two small ones close together at the ventral end of the lateral arm plate, the third is placed widely spaced on the dorsal part of the lateral arm plate, up to twice as long as the ventral spines in O. ljungmani , but shorter than an arm segment. The holotype of O. spinicantha may have lacked the second small ventral spine or McKnight (2003) may have mistaken it for a tentacle scale, when he described O. spinicantha as having only two spines at a distance from each other. Both species also have scattered spines on the dorsal disc (Fig. 2G), which are often rubbed off in preserved material. Morphologically similar to these species is Ophiura bathybia H.L. Clark, 1911, known from the North Pacific, and which appears to have more disc spines than the other two species and the dorsal arm spine is longer than an arm segment (Fujita et al. 2009). Genetically these three species are distinct, but closely related (Christodoulou et al. 2019; O’Hara unpublished data). Ophiura ljungmani has the widest reported depth range of the three, with 101–4150 m (Paterson 1985), but we suspect that the few shallowest records may be misidentifications of another species (possibly Ophiura acervata (Lyman, 1869) or Ophiura fallax Cherbonnier, 1959). Ophiura spinicantha was found by Galathea II at 2470–4470 m (Table 1), but type material was collected as shallow as 1585 m (McKnight 2003), and O. bathybia is known from 2869–4425 m (Lambert & Austin 2007), but was not found by this study. Geographically, O. ljungmani has been reported from both eastern and western sides of the North Atlantic Ocean and to South Africa (found by Galathea II only off West Africa, Tables 1, 2), whereas O. spinicantha appears to be restricted to southern Australia and New Zealand (here found in the Tasman Sea and Kermadec Trench, Table 2), and O. bathybia occurs in the North Pacific from Japan to the high Arctic (Djakonov 1954; Lambert & Austin 2007, Fujita et al. 2009).