Krohcoma, 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 : 78

Genus Krohcoma gen. nov.

urn:lsid:zoobank.org:act:0A950939-8454-48E0-853A-A431FB153F6F

Type species

Krohcoma mira sp. nov., by present designation.

Other species included

Krohcoma ampla sp. nov.

Diagnosis

Ophiacanthid genus with relatively stout LAPs devoid of conspicuous outer surface ornament; spine articulations very large, with thick dorsal and ventral lobes and very large muscle opening, freestanding on strongly elevated ridge, arranged in conspicuously dorso-proximally receding row; spine articulations not sharply separated from remaining outer surface; tentacle notch large to very large.

Etymology

Genus named in honour of my friend and colleague Andreas Kroh for his valuable support in the cladistic phylogenetic anaylsis of the Ophiacanthidae and in sampling the spectacular Glasenbach Gorge section, which produced the type species of the genus; from coma, Latin for “hair”, a commonly used suffix in ophiuroid names, gender feminine.

Remarks

Most fossil LAP types assignable to the Ophiacanthidae can be related to an extant lineage on the basis of strong morphological similarities. Among the more challenging fossil ophiacanthid LAP types is one which is characterised by very large, ear-shaped spine articulations arranged in a conspicuously dorso-proximalwards obliquely receding and ventrally protruding row, and displaying a large muscle opening. These relatively stout LAPs, unambiguously assignable to the Ophiacanthidae on account of the sigmoidal fold and the absence of a single large perforation on the inner side, furthermore display a very large tentacle notch. Although articulated specimens have yet to be discovered, it seems highly probable that the large tentacle notches, indeed, reflect large tentacle pores as defined by Thuy et al. (2012), which would place the LAP type in question among the basal, large-pored ophiacanthids formerly united as the Ophiotominae .

Among the currently known large-pored ophiacanthid lineages, Ophiotoma and the Lapidaster - Ophiologimus lineage clearly differ in having a non-bulging or elevated distal portion of their LAPs. The LAPs of Ophiolimna and Ophiopristis Verrill, 1899 display a conspicuous vertical striation on the outer surface and fundamentally different ridge structures on their inner side, and in Geromura gen. nov. the LAPs are extremely elongate. There is a superficial similarity to the LAPs of Eolaxoporus gen. nov., which, however, fundamentally differ in having proximally widely separate dorsal and ventral lobes of the spine articulations. Closest similarities are shared with the LAPs of Ophiomedea Koehler, 1906 and Leadagmara Thuy et al., 2012 . Neither of these, however, display a dorso-proximalwards receding row of spine articulations. Krohcoma gen. nov. is thus introduced here to accommodate the above-mentioned LAPs. Its exact phylogenetic position remains elusive. On the basis of LAP morphology, however, Krohcoma gen. nov. seems closest to Eolaxoporus gen. nov. and to the Ophiomedea - Leadagmara clade.