Ophiomitrella Verrill, 1899

Stöhr, Sabine, 2025, Two new species of brittle stars (Echinodermata: Ophiuroidea), living epizoic on a stalked crinoid, European Journal of Taxonomy 1022, pp. 176-201 : 182-187

Genus Ophiomitrella Verrill, 1899 Fig. 1; Table 2

Type species

Ophiacantha laevipellis Lyman, 1883 .

Material examined

ANTARCTICA – Maria Island • 1 spec., syntype of Ophioripa conferta ; depth 1300 fathoms ( 2379 m); 13 Dec. 1912; Australasian Antarctic Expedition; MNHN, MNHN-IE-2013-10230 (formerly Ec Os 20388) .

CHILE – Gulf of Ancud • 3 specs, syntypes of Ophiomitrella chilensis ; Paso Tenaún , S of Punta Tenaún; 42°20′50″ S, 73°22′00″ W; depth 70 m; 24 Jan. 1949; Lund University Chile Expedition stn M42; triangular dredge; hard bottom; SMNH, SMNH-Type-2321 .

INDONESIA – Kei Island • 1 spec., syntype of Ophiacantha tenuis ; 5°48.2′ S, 132°13′ W; depth 304 m; 1899–1900; Siboga Expedition stn 253; MNHN Ec Os 2040 .

NORWAY • 3 specs, syntypes of Ophiactis clavigera ; depth 364–546 m; 22 Oct. 1864; Uggla Expedition ; on Gorgonia ; SMNH, SMNH-Type-3724 .

SOUTH ATLANTIC OCEAN – Gough Island • 1 spec., syntype of Ophiomitrella ingrata ; depth 100 fathoms ( 183 m); 23 Apr. 1904; Scotia Expedition; MNHN, MNHN-IE-2013-10308 (formerly Ec Os 20364) .

WEST INDIES – off St. Vincent • 1 spec., paratype of Ophiacantha laevipellis ; depth 88 fathoms ( 160 m); 21 Feb 1879; Blake stn 232; MNHN, MNHN-IE-2013-10160 (formerly Ec Os 20398) .

Remarks

When Verrill (1899a) erected Ophiomitrella , he described it in a confusing dichotomous list, from which it is difficult to extract the characters that delimit this genus. Under section “ A ”, he sorted species in which the adoral shields are restricted to the proximal part of the oral shield, but under “ A.A. ” they extend around the oral shield. Ophiomitrella is found under “ B.B.”, which doesn’t mention adoral shields, but has uncovered radial shields, whereas “ B. ” is meant for species with covered radial shields. Finally, under “ n.n.”, Ophiomitrella has separated dorsal arm plates and thorny, slender arm spines that meet dorsally. The only species assigned to Ophiomitrella was O. laevipellis , making it the type species of the genus by monotypy. According to the redescription ( Verrill 1899b), Ophiomitrella should have small, widely separated radial shields, not bearing granules or spines, adoral shields limited to the proximal part of the oral shield, disc with scattered granules or stumps. In the same work ( Verrill 1899b), O. laevipellis is described as having long, narrow, covered radial shields, with only their distal part exposed, which was here confirmed by examination of publicly available photos of the holotype (MCZ:IZ:OPH-1957) and photos of a paratype taken by the author ( Fig. 1I–J).

Verrill subdivided Ophiomitrella , based on differences in arm spines, and placed O. laevipellis in one subgroup, whereas Ophiomitrella cordifera (Koehler, 1896) and Ophiomitrella globulifera (Koehler, 1896) formed the other subgroup. The latter two species match the description of the genus Ophiomitrella , which is however still a polyphyletic genus ( O’Hara et al. 2018), despite the recent transfer of a group of species to the morphologically highly similar genus Ophiosemnotes ( O’Hara & Thuy 2022) .

The necessary revision of these genera is far beyond the scope of this study, and as O’Hara & Thuy (2022) found, morphological characters that support the molecular clades have not been identified yet. In Table 2 , the species were grouped by the nature of their disc spines (granules are considered homologous to spines). The majority of the species have more or less spherical (granule-like) disc spines, and the removal of Ophiosemnotes brevispina (H.L. Clark, 1911) , that lacks disc spines, and Ophiosemnotes diaphora (H.L. Clark, 1911) , that has granules, from the Ophiosemnotes group concurs with the latest published molecular phylogeny ( Christodoulou et al. 2019). Thus, a revision of Ophiosemnotes appears necessary. However, on that tree, these two species are also in a separate clade from the remaining Ophiomitrella , and other members of this group are found in several clades on the molecular phylogeny ( Christodoulou et al. 2019), which suggests that the granular disc spine group may be polyphyletic. Several of the species with stellate disc spines form a clade on the molecular tree, but the clade includes also Ophiomitrella barbara Koehler, 1904 , which was here grouped as having elongated stumps, a character that is found in most of the species of Ophiosemnotes and in Ophiomitrella chilensis Mortensen, 1952 (see Fig. 2E), which has not been sequenced yet. Other characters, such as the shape of the adoral (trapezoid/crescent) and oral shields (rhombic, larger/smaller than adoral shields) and the size of the radial shields, vary between species without forming obvious groups. Thus, disc spines are the most promising phylogenetically informative character, but need to be differentiated in more detail, and additional characters need to be identified.

The issue is further complicated by the high similarity between Ophiomitrella and additional genera, which should also be re-assessed. Ophiomitra Lyman, 1869 shares with some Ophiomitrella not only the large adoral and small oral shield, but also the short, rounded radial shields. It was placed in Ophiotomidae Paterson, 1985 by O’Hara et al. (2018), but recent unpublished data (O’Hara pers. com.) suggest that its type species Ophiomitra valida Lyman, 1869 belongs in Ophiacanthidae instead. Ophiomitra leucorhabdota (H.L. Clark, 1911) falls into the Ophiotomidae clade, but several other species of Ophiomitra group with Ophiosemnotes ( Christodoulou et al. 2019) , which illustrates the genetic and morphological similarity between these genera. Last, but not least, the recently re-validated genus Ophiophthalmus Matsumoto, 1917 ( Nethupul et al. 2022) is also rather similar to Ophiomitrella , having short rounded radial shields, small disc granules, and large crescent-shaped adoral shields proximal to the rhombic oral shield.