Ophiosemnotes conferta

Ophiosemnotes conferta (Koehler 1922b)

Fig. 7A–B

Ophioripa conferta Koehler, 1922b: 19–21, pl. 85(9–13).

Ophiomitrella falklandica Mortensen, 1936: 256–259, figs. 8c–d, pl. 7(5) [according to O’Hara, 1990].

Ophiomitrella conferta.— Madsen 1967: 127.— O’Hara 1990: 299–300, fig. 2c–d, f–g.— O’Hara & Stöhr 2006: 90–92, fig. 10f–h, 18n–o.

Material examined. MD 50 CP7, MNHN IE.2009.1574 (5). MD 50 CP113, MNHN IE.2009.1575 (1). MD 50 DC146, MNHN IE.2009.1576 (14).

Distribution. East Indo-West Pacific (480–1019 m), South America (79–680 m), Kerguelen (247 m), southern Australia (590–2340 m), New Zealand (27–1365 m), Antarctic (74–835 m). SPA (420–1680 m).

Remarks. The MD 50 specimens are up to 7 mm dd, the disc scales coarse and imbricating with 1–2 stumps, to 0.6 mm high, vase-shaped to capitate, rough/thorny at tip (Fig. 7A). The radial shields are broadly triangular, and distally contiguous. There are three long cylindrical, blunt tipped oral papillae, sunken oral plates, and rhomboid oral shields. The VAPs are small and separate, with a notched distal edge (Fig. 7B). The LAPs bear up to six rounded arm spines, with a finely thorny surface, uppermost are longest, to 1.3 mm long, two times the length of a segment. The lowest arm spines have conspicuous ventrally directed thorns distally. The single tentacle scale is lanceolate.

These specimens are similar to the Southern Ocean O. conferta complex, characterised by the large capitate disc stumps. Following Madsen (1967), this complex has been placed in the genus Ophiomitrella Verrill, 1899b. However, the molecular phylogeny of O’Hara et al. (2017) shows that species placed in Ophiomitrella form several unrelated clades, one of which is a monophyletic group that contains O. conferta, O. ingrata Koehler, 1908, O. corynephora H.L. Clark, 1923 and O. clavigera (Ljungman 1865). There are two other available genus-level names that have been applied to at least one of these species. Matsumoto (1917) placed O. clavigera in his new genus Ophiosemnotes along with several North Pacific species including the type species O. tylota H.L. Clark, 1911. Koehler (1922b) originally placed O. conferta in Ophioripa Koehler, 1922a with type species O. marginata from the Philippines. We have not obtained DNA sequence for O. tylota or O. marginata, however, the sequenced specimens from this clade do conform to both generic morphological diagnoses, having large disc scales, sparse disc stumps, wide radial shields, small widely separate VAPs and DAPs, and short robust arm spines. They are clearly differentiated from the type of Ophiomitrella, O. laevipellis Lyman, 1883, which has small disc plates and tiny disc granules (mostly absent), widely separated radial shields, wide ventral arm plates, and numerous long slender arm spines. Consequently, we use the genus-name Ophiosemnotes for the O. conferta group as it has priority over Ophioripa, which may be a synonym. Another Ophiomitrella species that can be assigned to Ophiosemnotes is O. hamata Mortensen, 1933a. The inclusion of O. chilensis Mortensen, 1952 is questionable given the tiny tentacle scale and requires further investigation. Two species O. tylota and O. pachybactra share many features with O. conferta, however, the other North Pacific species now referred to Ophiosemnotes show a range of morphologies with several having tiny disc granules and naked circular separate radial shields (O. diaphora H.L. Clark, 1911, O. paucispina H.L. Clark, 1911) or no granules at all (O. brevispina H.L. Clark, 1911) and probably belong to other genera.

It is likely that there are several species within the O. conferta complex (O’Hara et al. 2017; O’Hara et al. 2013), which has been reported from upper bathyal depths from Antarctica to New Caledonia (O’Hara & Stöhr 2006). The disc stumps in particular are polymorphic, varying from spherical to capitate. Many Ophiosemnotes species, including O. conferta, are viviparous (O’Hara 1990) which potentially limits dispersal and species ranges. A thorough phylogeographical study of the complex is required to sort out species boundaries.