Ophiopetagno sp. 2

Thuy, Ben, Eriksson, Mats E., Kutscher, Manfred & Numberger-Thuy, Lea D., 2024, The beginning of a success story: basalmost members of the extant ophiuroid clade from the Silurian of Gotland, Sweden, European Journal of Taxonomy 947 (1), pp. 216-247 : 240

Ophiopetagno sp. 2

Figs 6I–J , 7

Material studied

NRM PAL Ec38345 .

Description

NRM PAL Ec38345 ( Fig. 6I–J ) is a dissociated median or distal lateral arm plate approximately 2.5 times as long as high, with weakly concave dorsal edge, convex distal edge and oblique proximal edge lined by shallow groove followed by very narrow band of more finely-meshed stereom; ventral portion long, weakly protruding ventro-proximalwards, with very weakly convex ventral edge lined by at least ten ambulacral groove spine articulations; outer surface with conspicuously coarse tuberculation covering entire outer surface except for groove along proximal edge and shelf distally bordering spine articulations, and consisting of trabecular intersections transformed into irregular, widely spaced tubercles; three moderately large lateral spine articulations, nearly equal-sized and equidistant along entire distal plate edge, separated from latter by relatively short shelf. Inner side of lateral arm plate ( Fig. 6J ) with very large, well-defined, prominent, rounded triangular vertebral articular surface in center of proximal plate portion at some distance from inner dorso-proximal corner and separated from slightly inwards protruding dorsal edge; tentacle notch large, shallow but well-defined, with large, shallow incision in ventral edge; at least ten small but well-developed ambulacral groove spine articulations along entire ventral plate edge.

Remarks

The single lateral arm plate described as Ophiopetagno sp. 2 stands out in having a very coarse outer surface ornamentation. In this respect, it bears a superficial similarity to the lateral arm plates of O. bonzo sp. nov. The latter, however, show a conspicuously oblique distal edge, smaller lateral spine articulations and fewer ambulacral groove spine articulations. In the absence of more specimens, we cannot assess the morphological variability of Ophiopetagno sp. 2 and therefore refrain from describing it formally as a new species.

Occurrence

Hoburgen.

Figures

Fig. 6. Dissociated lateral arm plates of ophiuroids from the Silurian of Gotland. A–B. Ophiopetagno doro sp. nov, holotype, NRM PAL Ec38341, proximal lateral arm plate in external (A) and internal (B) views. C–D. O. doro, paratype, NRM PAL Ec38342, median lateral arm plate in external (C) and internal (D) views. E–F. O. doro, paratype, NRM PAL Ec38343, distal lateral arm plate in external (E) and internal (F) views. G–H. Ophiopetagno sp. 1, NRM PAL Ec38344, proximal to median lateral arm plate in external (G) and internal (H) views. I–J. Ophiopetagno sp. 2, NRM PAL Ec38345, median to distal lateral arm plate in external (I) and internal (J) views. Abbreviations: AGSA = ambulacral groove spine articulations; di = distal; do = dorsal; LSA = lateral spine articulations; TN = tentacle notch; VAK = vertebral articular knob.

Fig. 7. Stratigraphic position of the taxa described in the present paper with their assumed evolutionary relationships and the nesting of the clades Ankhurida clade nov., Ophiovalida clade nov. and Metophiurida Matsumoto, 1913. Note that some lateral arm plates are mirrored to allow comparison in similar orientation.