Ophiolofsson archspire, 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 : 229-231

Ophiolofsson archspire gen. et sp. nov.

urn:lsid:zoobank.org:act:6613A01F-46C2-4E99-A187-A34C2199E3C5

Figs 4E–J , 7

Diagnosis

Species of Ophiolofsson gen. nov. with lateral arm plates showing very coarse, widely spaced tubercles on the outer surface, arranged in loose vertical rows; four relatively small lateral spine articulations along the entire distal plate portion; ambulacral groove spine articulations absent or very small and almost indiscernible; very shallow tentacle notch incision in ventral edge of median and distal lateral arm plates.

Etymology

Species named after Canadian, technical death metal band, Archspire, in recognition of their transcendent form of this music style while simultaneously building on the tradition formed by the progenitor bands.

Type material

Holotype

SWEDEN • Gotland, Lau Backar ; NRM PAL Ec 38330.

Paratypes

SWEDEN • 2 specs: same data as for holotype; NRM PAL Ec38331 , NRM PAL Ec38332 .

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. 4E–F )

NRM PAL Ec38330 is a small dissociated proximal lateral arm plate approximately 1.2 times as long as high, of rounded general aspect, with weakly convex dorsal and ventral edges and strongly convex distal edge; proximal edge weakly concave, with rounded dorsal and ventral edges, and with poorly defined, central depression encompassed by broad band of more finely-meshed stereom along proximal plate edge; outer surface with very coarse, widely-spaced tuberculation composed of enlarged trabecular intersections, arranged in loose, vertical rows and covering entire outer surface except for band of more finely-meshed stereom at proximal edge; four relatively small lateral arm spine articulations in vertical row at some distance from distal edge, equidistant, two central spine articulations largest; spine articulations poorly defined, rugose but strongly prominent, with small, inconspicuous central opening; ventralmost spine articulation at ventral edge of lateral arm plate; dorsalmost spine articulation close to dorsal plate edge; ventral edge of lateral arm plate without protrusions for ambulacral groove spine articulations. Inner side of lateral arm plate ( Fig. 4F ) with large, well-defined, weakly prominent, laterally elongate vertebral articular knob with large, shallow central depression; inner side of distal edge with two large, weakly prominent and poorly defined spurs; relatively large, deep and well-defined tentacle notch; ventral edge of lateral arm plate without incision for tentacle notch but with five small and vaguely visible ambulacral groove spine articulations.

Paratype supplements and variation

NRM PAL Ec38331 ( Fig. 4G–H ) is a small dissociated median lateral arm plate approximately 1.3 times as long as high; in agreement with holotype but with less strongly concave proximal edge; lateral arm spine articulations as in holotype; ventral edge with very weak incision for tentacle notch. Inner side of lateral arm plate as in holotype but with larger central depression in vertebral articular knob.

NRM PAL Ec38332 ( Fig. 4I–J ) is a small dissociated distal lateral arm plate approximately 1.5 times as long as high; dorsal and ventral edges very weakly convex to almost straight; proximal edge almost straight; outer surface as in holotype; three lateral arm spine articulations as in holotype, nearly equal-sized; ventral edge with very small incision for tentacle notch. Inner side with large, laterally elongate vertebral articular knob with large central depression; tentacle notch relatively large; ambulacral groove spine articulations invisible.

Remarks

The lateral arm plates of Ophiolofsson archspire gen. et sp. nov. stand out in having very coarse, widely-spaced outer surface tubercles arranged in loose vertical rows. It furthermore differs from its congeners in lacking clearly discernible ambulacral groove spine articulations and in showing a very weak tentacle notch incision in median to distal lateral arm plates.

Occurrence

Lau Backar and Gannor.

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.