Ophiolofsson joelmciveri, 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 : 224-226

Ophiolofsson joelmciveri gen. et sp. nov.

urn:lsid:zoobank.org:act:3DEE7765-50CE-4D7C-9FF4-CB437B923EF3

Figs 3A–D , 7

Diagnosis

Species of Ophiolofsson gen. nov. with lateral arm plates of rounded rectangular outline, with a convex dorsal edge; outer surface with a moderately coarse, dense tuberculation, up to three large, round spine articulations in the ventral half of the distal edge; up to five small, weakly protruding ambulacral groove spine articulations.

Etymology

Species named after prolific British author and music journalist, Joel McIver, for his unique ability to convey the cultural importance and impact of music.

Type material

Holotype

SWEDEN • Gotland, Nyhamn ; NRM PAL Ec38322 .

Paratype

SWEDEN • same data as for holotype; MnhnL NRM PAL Ec38323 .

Type locality and stratum

Llandovery Series, Telychian Stage, Pterospathodus amorphognathoides conodont Zone, Lower Visby Formation (units a and b); Nyhamn, Gotland, Sweden.

Description

Holotype ( Fig. 3A–B )

NRM PAL Ec38322 is a dissociated proximal lateral arm plate, approximately 1.3 times as long as high, with very weakly convex dorsal and ventral edges and straight distal edge; proximal edge slightly oblique, with very weak central incision and semi-circular depression dorsally and ventrally bordered by poorly defined, slightly prominent but not protruding oval knobs; outer surface with trabecular intersections enlarged into medium-sized, irregular tubercles, resulting in coarse overall appearance; tuberculation on entire outer surface except for depressed area near proximal edge; three large, approximately equidistant lateral arm spine articulations (LSA) freestanding in vertical row at some distance from distal edge; dorsalmost spine articulation at some distance from dorsal edge of lateral arm plate, with dorsal third of lateral arm plate devoid of spine articulations; ventralmost spine articulation at ventral edge of lateral arm plate; two central spine articulations largest; spine articulations consisting of single opening encompassed by elevated ring; ventral edge of lateral arm plate with very weakly visible protrusions of ambulacral groove spine articulations (AGSA). Inner side of lateral arm plate ( Fig. 3B ) with large, well-defined vertebral articulation knob with slightly depressed centre and situated directly at dorso-proximal corner of lateral arm plate; inner distal edge slightly depressed and separated from remaining inner surface by vertical ridge; large but relatively shallow tentacle notch (TN) on inner side; ventral edge of lateral arm plate without incision for tentacle notch but with four weakly developed ambulacral groove spine articulations.

Paratype (supplements)

NRM PAL Ec38323 ( Fig. 3C–D ) is a dissociated median to distal lateral arm plate approximately 1.5 times as long as high; overall, similar to holotype, but with convex distal edge, resulting in more rounded general outline; three spine articulations similar to those of holotype but with dorsalmost one missing; ventral edge of lateral arm plate with stronger protrusions of ambulacral groove spine articulations. Inner side as in holotype but with five instead of four ambulacral groove spine articulations.

Remarks

Ophiolofsson joelmciveri gen. et sp. nov. differs from its congeners in having large, round lateral spine articulations at some distance from the distal edge and restricted to the ventral part of the distal portion of the lateral arm plate. The closest similarities are shared with the stratigraphically close Ophiolofsson obituary gen. et sp. nov. However, there are distinctions: Ophiolofsson obituary features larger and vertically elongated spine articulations, a slightly coarser outer surface tuberculation, a concave dorsal edge, and larger, more pronounced ambulacral groove spine articulations.

Occurrence

Nyhamn and Ireviken.

Figures

Fig. 3. Dissociated lateral arm plates of ophiuroids from the Silurian of Gotland. A–B. Ophiolofsson joelmciveri gen. et sp. nov., holotype, NRM PAL Ec38322, proximal lateral arm plate in external (A) and internal (B) views. C–D. O. joelmciveri, paratype, NRM PAL Ec38323, median to distal lateral arm plate in external (C) and internal (D) views. E–F. Ophiolofsson obituary gen. et sp. nov., holotype, NRM PAL Ec38324, median to proximal lateral arm plate in external (E) and internal (F) views. G–H. O. obituary, paratype, NRM PAL Ec38325, proximal lateral arm plate in external (G) and internal (H) views. I–J. O. obituary, paratype, NRM PAL Ec38326, proximal median lateral arm plate in external (I) and internal (J) views. K–L. O. obituary, paratype, NRM PAL Ec38327, distal lateral arm plate in external (K) and internal (L) 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.