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.

Published as part of 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, pp. 216-247 in European Journal of Taxonomy 947 (1) on pages 238-240, DOI: 10.5852/ejt.2024.947.2631, http://zenodo.org/record/13365641