Ophiolofsson archspire Thuy & Eriksson & Kutscher & Numberger-Thuy 2024

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.