Lapidaster, 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 : 27

Genus Lapidaster gen. nov.

urn:lsid:zoobank.org:act:C21FF4FC-5361-44D5-ACC9-6AD5907BAC90

Type species

Lapidaster hystricarboris sp. nov., by present designation.

Other species included

Lapidaster caeloscopus sp. nov., Lapidaster coreytaylori sp. nov., Lapidaster etteri sp. nov., Sinosura fasciata Kutscher & Villier, 2003 , Lapidaster lukenederi sp. nov., Lapidaster mastodon sp. nov., Lapidaster mathcore sp. nov., Lapidaster wolfii sp. nov. and Lapidaster varuna sp. nov.

Diagnosis

Ophiacanthid with lateral arm plates displaying large tentacle notches; spine articulations not positioned on elevated ridge and not sunken into depressions or notches; ventral portion of lateral arm plate protruding ventro-proximally; generally single, poorly to moderately defined, spur on outer proximal and inner distal edge of lateral arm plate; inner side with single, well-defined ridge generally separated by rounded kink into dorsal and ventral halves.

Etymology

Name composed of lapis, Latin for “rock”, and aster, Greek for “star”, in reference to three species of the genus being named after rockstars; gender masculine.

Remarks

Lateral arm plates with a conspicuous, large tentacle notch combined with a strongly protruding ventroproximal portion of the plate and spine articulations which are neither on an elevated vertical ridge nor sunken in depressions of the distal plate edge are a common and morphologically diverse component of many Jurassic and Cretaceous ophiuroid assemblages (see below for details of distribution). The large ventral notches of the LAPs imply that the forms they belong to had large tentacle pores as defined by Thuy et al. (2012), which places them among the basal, large-pored ophiacanthid lineages formerly united as the subfamily Ophiotominae ( Paterson 1985) . Indeed, there are striking morphological similarities between the LAPs of the fossils considered here and those of extant Ophiologimus H.L. Clark, 1911 ( Fig. 11 : 1), in particular with regard to the development of the tentacle notch and the ventro-proximal portion of the plate, and the position and arrangement of the spine articulations. There are superficial similarities to the LAPs of extant Ophiotoma Verrill, 1899 . In that genus, however, the spine articulations generally are slightly sunken into depressions of the distal plate edge, and the ridge on the inner side of the plate displays two kinks instead of one.

As clearly shown by Thuy & Stöhr (2011), the greater the similarity between LAP morphologies, the more closely related the species in question are. In the present case, the above-mentioned fossil LAPs are so similar to the LAPs of Ophiologimus that they, indeed, belong to Ophiologimus or at least to a very closely related genus. The latter possibility is preferred here since the fossil LAPs differ, albeit only slightly, from those of Ophiologimus in generally displaying a spur on the outer proximal and inner distal plate edges. Thus, Lapidaster gen. nov. is erected here to accommodate dissociated fossil LAPs which are most closely similar to those of Ophiologimus . The great similarities in LAP morphology, however, strongly suggest that Ophiologimus and Lapidaster gen. nov. are sister taxa, although definite proof for the existence of an Ophiologimus - Lapidaster lineage can solely be gleaned from articulated specimens of Lapidaster gen. nov.

Figures

Fig. 11. Lateral arm plates (LAPs) of fossil and Recent ophiacanthid brittle stars in external (a) and internal (b) views. 1. Ophiologimus hexactis H.L. Clark, 1911, Recent, median LAP in external view. 2-4. Ophiologimus martynovi sp. nov. from the latest Aptian to earliestAlbian (Early Cretaceous) of Blake Nose, NE Atlantic. 2. GZG.INV.78532 (holotype), proximal LAP. 3. GZG.INV.78533 (paratype), median LAP. 4. GZG.INV.78534 (paratype), distal LAP. 5-6. Ophiologimus aiodipius sp. nov. from the latest Aptian to earliest Albian (Early Cretaceous) of Blake Nose, NE Atlantic. 5. GZG.INV.78536 (holotype), proximal LAP. 6. GZG.INV.78537 (paratype), median LAP. 7-8. Ophiologimus rugosus (Kutscher & Jagt, 2000) comb. nov. from the early Maastrichtian (Late Cretaceous) of Rügen, Germany. 7. GZG. INV.78539, proximal LAP. 8. GZG.INV.78540, median LAP. One common scale bar per species is given.