Ophiolofsson hendersonorum, Thuy & Eriksson & Kutscher & Numberger-Thuy, 2024

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 : 232-233

Ophiolofsson hendersonorum gen. et sp. nov.

urn:lsid:zoobank.org:act:A24BEBB4-3C6C-4E9F-93F1-2340AE5B416D

Figs 4K–P , 7

Diagnosis

Species of Ophiolofsson gen. nov. with lateral arm plates of rounded rectangular outline; outer surface with a moderately coarse, dense tuberculation; outer proximal edge with two spurs, a ventral one with an even surface and a smaller dorsal one with a convex, knob-like surface; up to five relatively small but prominent lateral spine articulations arranged in a continuous row along the entire distal plate edge; up to six large, conspicuous, protruding ambulacral groove spine articulations along the ventral plate edge.

Etymology

Species named after the Canadian couple, Tim and Sephora Henderson, for their work with the influential and pioneering metal music outlet, BraveWords.

Type material

Holotype

SWEDEN • Gotland, Lau Backar ; NRM PAL Ec38333 .

Paratypes

SWEDEN • 2 specs; same data as for holotype; NRM PAL Ec38334 , NRM PAL Ec 38335.

Type locality and stratum

Ludlow Series, Ludfordian Stage, uppermost part of the Lower Icriodontid conodont subzone sensu Jeppsson (2005), Eke Formation; Lau Backar, Gotland, Sweden.

Description

Holotype ( Fig. 4K–L )

NRM PAL Ec38333 is a large dissociated proximal lateral arm plate, almost as high as long, with weakly concave dorsal edge, weakly convex ventral edge and strongly convex distal edge; proximal edge irregularly convex, with a central depression ventro-distally bordered by large, prominent and well-defined oval spur (SP) with even surface, and dorso-distally by smaller, prominent but poorly-defined spur with convex surface; outer surface with moderately coarse tuberculation except in depressed area of outer proximal edge; five relatively small, equidistant lateral spine articulations, extending from dorsal to ventral plate edge, with weak dorsal decrease in size; ventral edge devoid of incision but with six protrusions for ambulacral groove spines articulations. Inner side of lateral arm plate ( Fig. 4L ) with large, prominent, poorly defined vertebral articular knob in dorso-proximal corner of plate, with large, deep central depression; inner distal edge with rounded, bulging dorsal and ventral corners; tentacle notch large but relatively shallow and poorly defined; five large, conspicuous ambulacral groove spine articulations all along ventral plate edge.

Paratype (supplements)

NRM PAL Ec38334 ( Fig. 4M–N ) is a large dissociated median to distal lateral arm plate approximately 1.3 times as wide as high, well in agreement with holotype but with less strongly convex distal edge; proximal edge with two conspicuous knobs as in holotype; outer surface ornamentation as in holotype; spine articulations similar to those of holotype but only four instead of five; ventral edge with six small, inconspicuous protrusions of ambulacral groove spine articulations. Inner side with large vertebral articular structure; inner distal edge as in holotype but with even surface on ventro-distal edge; six small, poorly defined ambulacral groove spine articulations all along ventral edge; tentacle notch as in holotype. NRM PAL Ec38335 ( Fig. 4O–P ) is a dissociated proximal to median vertebra, roughly cylindrical, approximately 1.3 times as long as high and slightly wider than high, with rounded triangular cross section and slightly constricted waist; large, articular surface on proximal part of lateral sides matching vertebral articular knob on inner side of lateral arm plates; water vessel canal entirely enclosed by vertebra; distal face with two large, comma-shaped, prominent, well-defined zygocondyles, dorsalwards converging and with more prominent ventral tip; opening of water vessel canal encompassed by zygosphene.

Remarks

The lateral arm plates of Ophiolofsson hendersonorum gen. et sp. nov. differ from those of their congeners in having two characteristic spurs on the outer proximal edge, the ventral one of which shows a conspicuous, even surface, and in having up to five relatively small lateral spine articulations arranged over the entire distal plate edge.

Occurrence

Lau Backar.

Figures

Fig. 4. Dissociated lateral arm plates and vertebra of ophiuroids from the Silurian of Gotland. A–B. Ophiolofsson immolation gen. et sp. nov., holotype, NRM PAL Ec38328, proximal lateral arm plate in external (A) and internal (B) views. C–D. O. immolation, paratype, NRM PAL Ec38329, median to distal lateral arm plate in external (C) and internal (D) views. E–F. Ophiolofsson archspire gen. et sp. nov., holotype, NRM PAL Ec38330, proximal lateral arm plate in external (E) and internal (F) views. G–H. O. archspire, paratype, NRM PAL Ec38331, median lateral arm plate in external (G) and internal (H) views. I–J. O. archspire, paratype, NRM PAL Ec38332, distal lateral arm plate in external (I) and internal (J) views. K–L. Ophiolofsson hendersonorum gen. et sp. nov., holotype, NRM PAL Ec38333, proximal lateral arm plate in external (K) and internal (L) views. M–N. O. hendersonorum, paratype, NRM PAL Ec38334, median to distal lateral arm plate in external (M) and internal (N) views. O–P. O. hendersonorum, paratype, NRM PAL Ec38335, vertebra in lateral (O) and distal (P) views. Abbreviations: AGSA = ambulacral groove spine articulations; AS = muscle attachment surface; di = distal; do = dorsal; LSA = lateral spine articulations; PB = podial basin; SP = spur; TN = tentacle notch; VAK = vertebral articular knob;WVC = water vessel canal; ZC = zygocondyle; ZS = zygosphene.

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.