Ophiolofsson immolation, 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 : 228-229

Ophiolofsson immolation gen. et sp. nov.

urn:lsid:zoobank.org:act:CF27D28D-2B22-449F-AC48-8F9468B09640

Figs 4A–D , 7

Diagnosis

Species of Ophiolofsson gen. nov. with lateral arm plates of almost oval outline; outer surface with a fine tuberculation; up to three small, weakly developed lateral spine articulations in a continuous row along the distal plate edge; up to five moderately large, but weakly developed ambulacral groove spine articulations.

Etymology

Species named after legendary American death metal band, Immolation, who came onto the scene slightly later than the above-mentioned Obituary.

Type material

Holotype

SWEDEN • Gotland, Tjälderviken ; NRM PAL Ec38328 .

Paratype

SWEDEN • same data as for holotype; NRM PAL Ec38329 .

Type locality and stratum

Wenlock Series, Whitwell Stage, Ozarkodina sagitta sagitta conodont Zone, Slite Group (upper part – “ Pentamerus gothlandicus beds” or equivalents); Tjälderviken, Gotland, Sweden.

Description

Holotype ( Fig. 4A–B )

NRM PAL Ec38328 is a dissociated proximal lateral arm plate approximately 1.3 times as long as high; dorsal edge very weakly convex, distal edge convex and proximal edge straight without central incision; narrow, poorly defined and distalwards concave depressed area at proximal edge; outer surface of lateral arm plate with fine, densely packed tubercles consisting of weakly enlarged trabecular intersections covering entire outer surface except for depressed area at proximal edge; three small lateral arm spine articulations, freestanding and weakly prominent spine articulations in vertical to slightly oblique row from ventral to dorsal edge of lateral arm plate; spine articulations relatively close to distal edge of lateral arm plate; ventral edge of lateral arm plate convex, with protrusions of five ambulacral groove spine articulations. Inner side of lateral arm plate ( Fig. 4B ) with large, well-defined vertebral articulation in dorso-proximal corner, with clearly depressed center; inner distal edge of lateral arm plate very weakly elevated and separated from remaining outer surface by low, moderately well-defined vertical ridge; large, moderately-defined tubercle notch distally sharply bordered by ridge of elevated distal edge; ventral edge of lateral arm plate without incision for tentacle notch but with five small, poorly-defined, nearly equidistant and equal-sized ambulacral groove spine articulations.

Paratype (supplements)

NRM PAL Ec38328 ( Fig. 4C–D ) is a dissociated median to distal lateral arm plate approximately 1.4 times as long as high; outline, outer surface ornamentation and spine articulations as in holotype; ventral edge with only four protrusions of ambulacral groove spine articulations.

Remarks

The lateral arm plates of Ophiolofsson immolation gen. et sp. nov. can be distinguished from their congeners by the fine outer surface tuberculation combined with three small, inconspicuous lateral arm spine articulations in a vertical row along the entire distal plate edge.

Occurrence

Tjälderviken and Filehajdar.

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.