Ophiozonella hexactis, Stöhr, Sabine, 2011

Stöhr, Sabine, 2011, New records and new species of Ophiuroidea (Echinodermata) from Lifou, Loyalty Islands, New Caledonia, Zootaxa 3089, pp. 1-50 : 39-40

Ophiozonella hexactis sp. nov.

Figure 18

Type material. Holotype on SEM stub, sta. 1461, New Caledonia, Loyalty Islands, Lifou, reef Shelter, 20°54'S, 167°02.1'E, 100–120 m [ MNHN IE- 2009-9209]. 1 paratype, sta. 1467, in ethanol [SMNH-Type-8081].

Other material. SOL4934 14Gr23, Australia, Joseph Bonaparte Gulf, 10°18.517'S, 129° 37.01'E, 87 m [MoV- F 171262]; SS10/2005 96, Australia, Kalbarri, 27°48.48'S, 113°17.82'E, 123– 112 m [MoV-F 111958]; SS10/2005 105, Australia, Zuytdorp, 27°8.01'S, 112°46.06'E, 414– 405 m [MoV-F 111983].

Etymology. The specific name is derived from the Greek words hex meaning six and actis meaning ray.

Holotype description. Disk irregular hexamerous, a larger and a smaller half, showing clear signs of fission, 1.4–2.0 mm dd. All arms broken, at least 2 times dd, three smaller, three larger. Disk covered by round, imbricating scales, irregularly placed, centrodorsal clearly distinguishable. Radial shields hardly larger than disk scales, round, contiguous except at proximal end, overlapped by disk scales. Dorsal arm plates rounded triangular with straight distal edge, consecutive plates widely separated by lateral plates. No accessory dorsal arm plates. Two conical arm spines, about 1/3 as long as an arm joint, distally turning into multi-toothed hooks.

Ventral disk covered by small, round imbricating scales. Genital slits do not extend to the disk edge. The six jaws all vary in the size of the plates and papillae. Oral papillae consist of a pointed apical papilla, three low oval lateral papillae at dental and oral plate, and a wide low distal papilla at oral plate and adoral shield edge. Adoral shields elongated triangular with flaring distal ends. Oral shields all of different size, the largest elongated triangular with straight edges and a hydropore on its proximal part, a tiny triangular one, a broken triangular one possibly with hydropore, another medium sized rounded triangular one with hydropore, a tiny pentagonal one and a dropshaped one with convex distal edge. Second tentacle pore completely inside the mouth angle. Ventral arm plates pentagonal, about as long as distal width, with strongly concave lateral edges, slightly convex distal edge, consecutive plates widely separated by lateral plates. A single large, round tentacle scale at each pore. Spine articulation of two parallel ridges, connected proximally.

Paratype variations. The paratype measures 1.6–1.7 mm dd, and resembles the holotype in the disk scalation, arm plates and oral frame. It has likewise three smaller and three larger arms and a distorted disk showing signs of regeneration after fission. The younger arms are longer than in the holotype and on the distalmost joints the dorsal spine is distinctly hook-shaped. One of these arms has an intact tip with an elongated conical terminal plate with distal opening.

Remarks. Matsumoto (1915) erected Ophiozonella to separate deep water forms from littoral forms placed in Ophiozona , now a synonym of Ophiolepis ( Devaney 1974b) . One of the main differences between Ophiozonella and Ophiozona / Ophiolepis is supposed to be the absence of a distinct trio of plates distal to each pair of radial shields in Ophiozonella (but see below). The new species lacks these plates and its large disk scales and oral and adoral shields also fit with the description of Ophiozonella . It also lacks accessory dorsal arm plates that are typical for Ophiolepis ( Matsumoto 1915; Devaney 1974b). The genus until now included 31 species ( Stöhr & O’Hara 2007), which are rather heterogeneous in appearance. The type species, O. longispina ( H.L. Clark, 1908) , is a large species reaching more than 10 mm dd, with well differentiated skeleton of numerous plates and scales. Other species are small, a few millimetres in diameter, with reduced skeleton and paedomorphic appearance, such as O. novaecaledoniae Vadon, 1990 . The new species is the only hexamerous, fissiparous species in the genus and thus distinguished from all others. Its maximum size is unknown, but many fissiparous ophiuroids are small and need a long time to reach their final size due to repeated fission and regeneration ( Mladenov & Emson 1988).

The genus Ophiozonoida bears great resemblance to Ophiozonella . According to the description of the type species Ophiozonoida picta H.L. Clark, 1915 , it is distinguished by infradentally placed apical mouth papillae, erect arm spines, a single large tentacle scale and small scales interspersed with larger plates on the dorsal disk ( Clark 1915). Since Spencer & Wright (1966) synonymized Ophiotylos with Ophiozonoida , the genus includes six species, most of which are small, under 5 mm in disk diameter. Liao &Clark (1995) remarked that the species previously assigned to Ophiotylos may actually be misidentified young of Ophiolepis , due to their small size and underdeveloped skeleton. The remaining species may likewise be young of Ophiolepis or Ophiozonella , except for the type species O. picta , which has been reported with up to 10 mm disk diameter ( Mortensen 1924). Among the unidentified species from Lifou, the Ophiozonella sp. from sta. 1440 ( Table 2) has a colour pattern similar to the image of O. obscura Koehler, 1922 shown in Koehler (1930) and agrees in most characters with it, except at a disk diameter of 3.8 mm it is larger than Koehler's specimen and it has small scales between the larger disk plates, which suggests it may be the young of an Ophiolepis . Further examination and revision of all species of Ophiozonoida are needed to resolve their status.

Distribution. Known from Lifou, northern Australia (Timor Sea) and southwest Australia (Indian Ocean). Most of the species of Ophiozonella live in the deep sea, from a few hundred to several thousand meters deep. However, the locality (Uraga Channel, Japan) of the type species, O. longispina , was only 128 m deep. The holotype of Ophiozonella hexactis sp. nov. was collected at 100–120 m, the paratype at just 90 m, and the Australian material at 87– 414 m.

Figures

FIGURE 18. SEM images of Ophiozonella hexactis nov. sp., holotype MNHN IE- 2009 - 9209. A, dorsal aspect, showing signs of regeneration with three smaller and three larger arms and an irregular disk; B, ventral aspect; C, oral frame and ventral interradii, note the large distal oral papilla; D, dorsal arm; E, ventrolateral arm; F, hook-shaped distal arm spines; G, arm spine articulation and tentacle scale. Scale bars in millimetre.