Ophiolimna Verrill, 1899

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 : 65

Genus Ophiolimna Verrill, 1899

Type species

Ophiolimna bairdi Lyman, 1883 , by original designation.

Diagnosis

LAPs with at least part of their outer surface covered by a well-developed, coarse vertical striation composed of broad, overlapping lamellae; spine articulations sunken into notches of the distal edge and partly overlapped by the strongly undulose distalmost lamella and connected with the latter by the large, tongue-shaped ventral lobe of the spine articulations; inner side with central ridge, commonly with widened or bifurcated dorsal tip, and ventral ridge, in direct continuation of central ridge or connected with the latter.

Remarks

The LAPs of extant Ophiolimna ( Fig. 13 : 4-6) are among the most distinctive of the currently known ophiacanthids. The well-developed, coarse vertical striation of the outer surface consisting of broadly overlapping lamellae, and the spine articulations overlapped by the undulose distalmost lamella and connected with the latter by the large, tongue-like ventral lobes of the spine articulations are found in no other type of ophiacanthid LAP morphology. There is, however, a superficial resemblance with the LAPs of extant Ophioconis Lütken, 1869 , currently assigned to the Ophiodermatidae Ljungman, 1867 ( Stöhr & O’Hara 2007), as already pointed out by Martynov (2010). However, the LAPs of the two genera can easily be told apart on the basis of the ridges on the inner side of the proximal LAPs: while in Ophiolimna there is one large, central ridge with a second ventral one indirect continuation of the former, Ophioconis displays three round knobs instead of true ridges. Ophiolimna and Ophiotoma share a very similar development of the ridges on the inner side of the LAPs, which underpins their close phylogenetic ties.

The ophiacanthid fossil record includes a number of rare occurrences, from both shallow- and deepwater settings, of dissociated LAP types which closely recall the LAPs of extant Ophiolimna . In fact, they fit the LAP-morphological diagnosis of Ophiolimna so well that they almost certainly belong to Ophiolimna or at least to a very closely related genus.

Figures

Fig. 13. Lateral arm plates (LAPs) of fossil and Recent ophiacanthid brittle stars in external (a) and internal (b) views. 1-3. Ophiotoma incredibilis sp. nov. from the latest Aptian to earliest Albian (Early Cretaceous) of Blake Nose, NE Atlantic. 1. GZG.INV.78549 (holotype), proximal LAP. 2. GZG. INV.78550 (paratype), median LAP. 3. GZG.INV.78551 (paratype), distal LAP. 4. Ophiolimna antarctica (Lyman, 1879), Recent, proximal LAP. 5-6. Ophiolimna perfida (Koehler, 1904), Recent. 5. Proximal LAP. 6. distal LAP. 7-8. Ophiolimna tiamatia sp. nov. from the late Sinemurian to early Pliensbachian (Early Jurassic) of the Glasenbach Gorge, Austria. 7. NHMW 2012/0137/0010 (holotype), proximal LAP. 8. NHMW 2012/0137/0011 (paratype), median LAP. 9-12. Ophiolimna malagasica sp. nov. from the Bathonian (Middle Jurassic) of Jumara, India. 9. GZG.INV.78553 (holotype), proximal LAP. 10. GZG.INV.78554 (paratype), median LAP. 11. GZG.INV.78555 (paratype), median LAP. 12. GZG. INV.78556 (paratype), distal LAP. One common scale bar per species is given.