Lapidaster etteri, Thuy, 2013

Thuy, Ben, 2013, Temporary expansion to shelf depths rather than an onshore-offshore trend: the shallow-water rise and demise of the modern deep-sea brittle star family Ophiacanthidae (Echinodermata: Ophiuroidea), European Journal of Taxonomy 48, pp. 1-242 : 39-42

Lapidaster etteri sp. nov.

urn:lsid:zoobank.org:act:DFBC69CF-37F1-4D39-A8F3-D8DA46708D05

Fig. 9 : 1-5

p.p. Ophiopholis ? trispinosa Hess, 1965a: 1067, 1075 , figs 16, 38-40 (non figs 36-37, referable to Ishidacantha trispinosa (Hess, 1965) comb. nov.)

Diagnosis

Species of Lapidaster gen. nov. with relatively large LAPs showing a weak constriction, a widened dorsal tip of the ridge on the inner side and a thickened ventral part.

Etymology

Species named in honour of Walter Etter (Naturhistorisches Museum Basel, Switzerland), who generously provided access to the original material of Hans Hess’s pioneering studies on ophiuroid micropalaeontology, inclusive of the type material of the new species.

Type material

Holotype NHMB M11209 .

Paratypes

NHMB M11210, NHMB M11211, NHMB M11212 and NHMB M11213.

Type locality and horizon

Longecombe, France; Renggeri Member, Bärschwil Formation, early Oxfordian, Late Jurassic.

Additional material

304 dissociated LAPs from Longecombe, France, the original material of Hess (1965a); 7 dissociated LAPs from Chapois, France, the original material of Hess (1965a).

Description

Holotype

NHMB M11209 is a dissociated, medium-sized proximal lateral arm plate, slightly wider than long, with strongly concave proximal edge and strongly convex distal edge; ventro-proximal quarter of LAP protruding ventro-proximalwards; slight constriction, resulting in slightly concave dorsal edge; horizontal, elongate, moderately well-defined and prominent spur close to ventro-proximal tip of LAP. Outer surface with coarsely reticulate stereom with thickened trabeculae; trabeculae without tendency to develop into vertical striation; coarsely reticulate stereom evenly surrounding all spine articulations, grading into finely meshed stereom close to proximal edge. Four large, ear-shaped spine articulations, freestanding in continuous row close to distal edge of LAP, dorsal and ventral lobes forming continuous volute in all spine articulations; proximal edge of dorsalmost spine articulation overlapped by finely reticulate stereom; ventralmost and dorsalmost spine articulations smaller than two median ones; dorsalward increase in size of gaps separating spine articulations. Ventral edge of LAP with large, conspicuous and gently concave tentacle notch.

Inner side of LAP with sharply defined, narrow, prominent ridge; dorsal half of ridge oblique and nearly straight, with rounded tip nearly twice wider than remaining dorsal half of ridge and not reaching dorsal or proximal edges of LAP; ventral half of ridge slightly wider than dorsal half, separated from the latter by rounded kink, less sharply defined and prominent than dorsal half but not confluent with thickened ventral edge of LAP. Single irregular perforation discernible on inner side of LAP near tentacle notch. Small, moderately well-defined, prominent and slightly oblique ridge on inner side of ventro-distal tip of LAP. Inner side of tentacle notch with coarsely reticulate and horizontally stretched stereom.

Paratype supplements and variation

NHMB M11210 is a dissociated median lateral arm plate, wider than high. Overall morphology well in agreement with that of holotype. Constriction stronger than in holotype, resulting in clearly concave dorsal edge of LAP. Spur near ventro-proximal edge of LAP poorly defined, hardly discernible. Three spine articulations in continuous row; median spine articulation slightly larger than others. Ventral edge of LAP with large, conspicuous tentacle notch.

Inner side with well-defined, narrow, prominent ridge; dorsal half of ridge strongly oblique, straight, with slightly widened dorsal tip; ventral half of ridge wider than dorsal one but less well-defined, not confluent with thickened ventral edge of LAP. Small, very poorly defined and barely prominent spur on inner side of ventro-distal edge.

NHMB M11211 is a dissociated distal LAP, almost three times wider than high, of rectangular to barlike outline; distal edge gently convex, proximal edge concave; slight constriction, resulting in very gently concave dorsal edge and clearly concave ventral edge of LAP; no spurs discernible on outer proximal edge. Two spine articulations, nearly equal in size. Large tentacle perforation near ventral spine articulation.

Inner side with two very small, irregular, diffuse, slightly prominent and widely separate knobs. Large tentacle perforation in centre of distal half of LAP.

NHMB M11212 is a median arm fragment composed of two articulated segments. LAPs well in agreement with type specimens; ventral arm plates T shaped, with narrow proximal half, concave lateral edges, distal half almost three times wider than proximal half, distal edge straight to slightly concave. Tentacle openings clearly larger than half the width of the ventral arm plates. Dorsal arm plates very thin, wedge shaped, with strongly acute proximal angle, outline of distal edge not clearly discernible. Single arm spine preserved, attached to ventral spine articulation, conical, with coarse outer surface, broken tip but probably not much longer than half the width of a LAP.

NHMB M11213 are two distal arm fragments composed of five intact arm segments. One LAP preserving two arm spines in place, ventral one broken, dorsal one intact, shorter than half the width of a LAP, conspicuously claw shaped with point facing ventralwards.

Remarks

When Hess (1965a) described a new species, Ophiopholis ? trispinosa , on the basis of dissociated LAPs and articulated arm fragments from the Oxfordian of France, he lumped two entirely different LAP types under a single species. A re-examination of the original material has now revealed that one type, figured in the original description ( Hess 1965a: figs 16, 38-40) along with the second type, bears a striking similarity to the LAPs of extant Ophiologimus . The presence of a spur on the outer proximal and inner distal edges places this type of LAPs in Lapidaster gen. nov. In view of the fact that the holotype of O.? trispinosa is a LAP of the second type (see below for a detailed reassessment), however, the species name cannot be used for the LAPs assigned to Lapidaster gen. nov. The latter are therefore here described as a new species. Greatest similarities are shared with the LAPs of Lapidaster lukenederi sp. nov., especially on account of the slight constriction. The LAPs of Lapidaster etteri sp. nov., however, differ in being more markedly thickened near their ventral edge and in having a better-developed spur on the outer proximal and inner distal edges and a dorsally widened tip of the ridge on the inner side.

Lapidaster etteri sp. nov. is the sole species of the genus of which arm spines and ventral and dorsal arm plates are available. Hook-shaped spines on distal arm segments, as observed in the articulated arm fragments of L. etteri sp. nov. described above are commonly found in extant species of Ophiologimus (e.g. O’Hara & Stöhr 2006; Martynov 2010). In addition, tentacle pores of the distalmost arm segments developed as within-plate perforations rather than between-plate openings, as observed in L. etteri sp. nov., are regularly seen in extant species of Ophiologimus . The hook-shaped arm spines and within-plate tentacle openings in distalmost arm segments provide additional evidence for the close ties between both genera.

Occurrence

Early Oxfordian of France.

Figures

Fig. 9. Fossil lateral arm plates (LAPs) of ophiacanthid brittle stars in external (a) and internal (b) views and articulated arm fragments. 1-5. Lapidaster etteri gen. et sp. nov. from the early Oxfordian (Late Jurassic) of Longecombe, France. 1. NHMB M11209 (holotype), proximal LAP. 2. NHMB 11210 (paratype), median LAP. 3. NHMB M11211 (paratype), distal LAP. 4. NHMB M11212 (paratype), distal arm fragment in lateral view. 5. NHMB M11213 (paratype), distal arm fragment in dorsal (a) and ventral (b) views. 6-8. Lapidaster mastodon gen. et sp. nov. from the late Oxfordian (Late Jurassic) of the Plettenberg, Germany. 6. GZG.INV.78517 (holotype), proximal LAP. 7. GZG.INV.78518 (paratype), median LAP. 8. GZG.INV.78519 (paratype), distal LAP. One common scale bar per species is given, except for 4 and 5.