Eolaxoporus, 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 : 21-22

Genus Eolaxoporus gen. nov.

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Type species

Eolaxoporus hagdorni sp. nov. by present designation.

Other species included

Eolaxoporus imminens sp. nov.

Diagnosis

Ophiacanthid with lateral arm plates of rectangular outline displaying large tentacle notches; welldeveloped constriction, outer surface without conspicuous ornamentation; two spurs on the outer proximal and inner distal edges; spine articulations with near-parallel, proximally widely separated dorsal and ventral lobes connected distally by sigmoidal fold; tongue-shaped, dorso-proximalwards bent ridge devoid of kinks and widened parts on the inner side.

Etymology

Name composed of Eos , the Greek goddess of the dawn, laxus, Latin for “wide”, and porus, Latin for “pore”, in allusion to the fact that this genus represents one of the oldest members of the large-pored ophiacanthid lineages; gender masculine.

Remarks

Small dissociated lateral arm plates with conspicuously large tentacle notches, a well-developed constriction resulting in an elevated distal part, and spine articulations composed of proximally widely separated dorsal and ventral lobes connected distally by a sigmoidal fold are the commonest and stratigraphically most widely distributed ophiacanthid remains in Triassic shallow-water deposits. The peculiar structure of the spine articulations seems misleading at first, but the presence of a sigmoidal fold (as defined by Martynov 2010) undoubtedly places the present LAP type in the Ophiacanthidae . The size of the tentacle notches implies that the corresponding tentacle pores were large as defined by Thuy et al. (2012). This refers the present LAP type among the basal, large-pored ophiacanthid lineages formerly united as the subfamily Ophiotominae Paterson, 1985 ( Paterson 1985) .

Indeed, there is a certain resemblance to the LAPs of extant Ophiologimus and, on account of the presence of spurs on the outer proximal and inner distal edges, even a closer match with the LAPs of extinct Lapidaster gen. nov. The structure of the spine articulations, however, differs fundamentally. A new genus, Eolaxoporus gen. nov., is thus erected here to accommodate the LAP type in question. Phylogenetic relations with other large-pored ophiacanthid lineages, however, remain elusive until articulated specimens of this new genus are discovered.

The LAPs described as Ophiacantha ? binitorulosa Kristan-Tollmann, Tollmann and Hamedani, 1979 from the Rhaetian of Iran, are probably assignable to Eolaxoporus gen. nov., in particular in view of the nearparallel dorsal and ventral lobes of the spine articulations. In the absence of SEM-supported re-examination of the type material, however, assignment to Eolaxoporus gen. nov. must be treated as questionable. On the basis of the drawings in Kristan-Tollmann et al. (1979), it cannot be decided whether the LAPs of O.? binitorulosa

display a sigmoidal fold or not; this means that that species cannot even be considered as an unquestionable ophiacanthid record.The LAPs figured by Kristan-Tollmann & Gramann (1992) as Ophiacantha ? binitorulosa from the Rhaetian of the Exmouth Plateau are too poorly preserved to be identifiable.