Ophiopetagno sp. 1

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 : 238-240

Ophiopetagno sp. 1

Figs 6G–H , 7

Material studied

NRM PAL Ec38344 .

Description

NRM PAL Ec38344 ( Fig. 6G–H ) is a dissociated proximal or median lateral arm plate approximately 1.8 times as long as high, with weakly concave dorsal edge, convex distal edge and oblique proximal edge lined by shallow groove; ventral portion long, weakly protruding ventro-proximalwards, with weakly convex ventral edge with central protrusion caused by three ambulacral groove spine articulations; outer surface with very fine tuberculation covering entire outer surface except for groove along proximal edge and shelf distally bordering spine articulations; large, dorsally rounded, moderately well-defined elevation in middle of outer surface; three small, inconspicuous lateral spine articulations directly at distal edge of central elevation on outer surface, with larger gap between dorsal and middle articulations, separated from distal plate edge by very large shelf. Inner side of lateral arm plate ( Fig. 6H ) with large, oval to 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 small, shallow but well-defined, with small but deep incision in ventral edge; three small, inconspicuous ambulacral groove spine articulations grouped in protruding part of ventral plate edge proximally bordering tentacle notch.

Remarks

The single lateral arm plate described herein as Ophiopetagno sp. 1 differs from those of its congeners in being much larger, having a very fine outer surface ornamentation and a central elevation, very small, inconspicuous lateral spine articulations, and ambulacral groove spine articulations reduced to a group on a protrusion of the ventral edge. The lateral arm plate in question clearly belongs to a new species but in the absence of more material allowing for assessment of the intraspecific variability, we refrain from formally naming it.

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.