Actinozonella texturata ( Lyman, 1883 ) Lyman, 1883

Stöhr, Sabine, 2011, New records and new species of Ophiuroidea (Echinodermata) from Lifou, Loyalty Islands, New Caledonia, Zootaxa 3089, pp. 1-50 : 42-44

Actinozonella texturata ( Lyman, 1883) , new combination

Figure 20

Ophiomastus texturatus Lyman, 1883: 247 –248, pl. IV, figs 49–51. Ophioglypha humilis Koehler, 1904 : pl. VII, figs 1–3. New synonymy. Ophiozonella humilis – Koehler 1930: 254.

Amphiophiura humilis – H.L. Clark 1915: 310.

Type locality. Fiji, off Matuku, "Challenger" sta. 173, 19°9'35''S, 179°41'50''E, 315 fms (= 576 m), coral mud, 24 July 1874, dredged.

Material. Sta. 1468: 1 spm; sta. 1650C:>50 spms.

Description. Figured specimen from sta. 1650C with dorsal disk 4.7 mm dd, covered with a round centrodorsal plate, encircled by 7 small trapezoidal plates, an outer circle of 10 larger pentagonal plates, interradial columns of 2–3 rectangular plates, interspersed by a few smaller plates at the outer circle. Radial shields triangular, about half of disk radius long, completely separated by series of 4 rectangular plates similar to the interradial series. The distalmost of these radial plates forms the centre of a trio of plates on the arm base distal to the radial shields. Dorsal arm plates contiguous, fan-shaped, slightly wider than long, with convex to angular dorsal edge. Lateral arm plates massive. All plates with tuberculous microstructure. Three short conical arm spines, about as long as half an arm joint, appressed.

Ventral disk covered by a wide marginal plate that is the extension of the distal dorsal interradial plate, a narrow rectangular plate three times as long as wide, and two large genital plates as long as the entire interradius. Genital slits restricted to proximalmost arm joint, inconspicuous, lacking papillae. Jaws with small papilliform apical papilla and three low, wide, scale-like lateral papillae. Adoral shields curved, distally flaring, abutting the proximal edges of the oral shield, not separating it from the arm. Oral shield fan-shaped with acute proximal angle and convex distal edge, slightly wider than long. Ventral arm plates small, slightly wider than long, widely separated by lateral plates, pentagonal with straight distal edge and convex lateral edges. A single round tentacle scale at each pore, on the lateral plate. Tentacle pores along entire arm.

Internal skeleton: oral plates elongated and strongly arched, with a small round abradial muscle attachment area. Dental plate somewhat cup-shaped convex, dorsal tooth fenestration elongated and placed at an angle, middle one shorter and almost horizontal, ventral one an oval opening. On internal side of dental plate several holes indicate positions of ventral and middle fenestration, but not the dorsal one. Proximal vertebrae with typical zygospondylous articulation and not elongated much, with wide, winglike proximal muscle flanges. Their lateral structure shows a complex pattern of muscle flanges, a central process and grooves. Proximal lateral arm plates about as long as high, strongly convex, with a tuberculous external stereom, except where two plates meet and overlap ventrally. Internal side strongly excavated proximally, bearing two smooth distal patches and a slightly off-centre nerve opening. Spine articulations on proximal arm consist of two parallel ribs with muscle and nerve opening between them. Distalwards lateral plates more and more elongated and more convex. Abradial genital plate massive, with convex outer and straight inner edge. An adradial genital plate was not identified and may be absent. Radial shields on the same animal differ in shape, some with a straight inner edge and some with an almost rhombic shape. Their internal side is depressed distally, but shows no obvious socket to form a joint with the genital plate.

Variations. The scalation pattern of the dorsal disk is highly variable in the sample at hand. In smaller specimens the scales in the circle next to the centrodorsal are smaller and their number varies from four to eight. When there are five of them they are placed interradially and this is most likely the basic, undisturbed pattern. These are cleary secondary plates developing after the primaries and probably other plates. The larger radial plates in the following circle are present in all specimens and most likely represent the primary plates. Several specimens lack distinct circles of plates. Instead, the centre of the disk is covered by a random looking assortment of unidentifiable plates. This may suggest regeneration after damage. One specimen from sta. 1650C is hexamerous with a deformed disk on which the primaries cannot be distinguished.

Remarks. It should be noted that Lyman (1883) included this and two other Indo-Pacific species from the "Challenger" expedition in his report on the "Blake" expedition to the West Indies. He particularly remarked on the pattern of the disk plates with 11 central plates and ten radiating lines of single plates, which are a unique characteristic of this species, clearly visible also in Koehler's (1904) illustration. Actinozonella texturata and O. humilis are thus conspecific. A new genus is proposed for this species, since it does not fit well with either Ophiomastus or Ophiozonella , nor with any other known genus, which is also reflected by the fact that the species has been transferred between several genera. Ophiomastus is described as the disk being covered with little more than the primary plates and all included species show a strongly paedomorphic morphology, suggesting that some may actually be the juveniles of other species. Actinozonella texturata has a larger number of disk plates.

Actinozonella differs from Ophiozonella in the shape of the oral papillae, particularly the absence of an operculiform distal papilla, the presence of a superficial second tentacle pore and the small tentacle scales. This species may be placed in the family Ophiuridae , subfamily Ophiurinae , due to its superficial second oral papilla, a character regarded as critical for this subfamily. However, the absence of genital papillae and an arm comb, the short genital slits, the large disk plates and the trio of plates distal to the radial shields are similar to genera in the family Ophiolepididae (compare Ophiozonella above). Indeed, A. texturata had originally been placed in that family, since Matsumoto (1915) placed Ophiomastus in Ophiolepididae , subfamily Ophiomastinae . Koehler (1930) recognized these affinities when he revised his original opinion on O. humilis . Matsumoto (1917) remarked on the juvenile appearance of many species in Ophiolepididae , and the position of the second tentacle pore outside the mouth used to delimit Ophiurinae is a juvenile character ( Sumida et al. 1998; Stöhr 2005). Its validity as a character for family delimitation is thus questionable. Pending a much needed revision of Ophiurinae and Ophiolepididae , since all other characters point to Ophiolepididae , I propose to place A. texturata in this family.

Figures

FIGURE 20. SEM images of Actinozonella texturata. A, dorsal aspect; B, ventral aspect; C, dorsal arm; D, ventral arm; E, dorsolateral arm; F, oral plate (half-jaw), abradial aspect; G, oral plate, adradial aspect; H, dental plate, external; I, dental plate, internal; J, proximal vertebra, proximal face; K, proximal vertebra, lateral aspect; L, proximal vertebra, distal face and dorsal; M, proximal lateral arm plate, external; N, proximal lateral arm plate, internal; O, spine articulations on lateral arm plate; P, ar m spine, showing articulation; Q, distal lateral arm plate external; R, distal, lateral arm plate internal; S, abradial genital plate; T, distal vertebra, dorsal; U, radial shield, internal. Oral plates and radial shield orientated with distal end left, dental plates with dorsal side up. Scale bars in millimetre.