Thuy B et al. (2020), A new ophiacanthid brittle star (Echinodermata,...

ECB-ART-49629

PeerJ 2020 Jan 01;8:e9671. doi: 10.7717/peerj.9671.

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A new ophiacanthid brittle star (Echinodermata, Ophiuroidea) from sublittoral crinoid and seagrass communities of late Maastrichtian age in the southeast Netherlands.

Thuy B , Numberger-Thuy L , Jagt JWM .

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A new species of brittle star, Ophiomitrella floorae, is recorded from the lower two meters of the Gronsveld Member (Maastricht Formation), of late Maastrichtian age (c. 66.7 Ma). These relatively fine-grained biocalcarenites reflect shallow-water deposition in a sheltered setting with a relatively firm sea floor and clear waters, under middle sublittoral and subtropical conditions. Associated echinoderm taxa comprise more robust, sturdy-plated ophiomusaid and ophiodermatid brittle stars and numerous bourgueticrinine sea lilies. The new brittle star described herein belongs to a family whose present-day members are predominantly restricted to bathyal depths. Its small size and the exceptional preservation of a single articulated specimen partially wrapped around the stalk of a bourgueticrinine suggest that O. floorae n. sp. was probably epizoic and specifically associated with stalked crinoids.

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	Figure 1. Locality map.Map of southern Limburg and contiguous areas in Belgium and Germany, representing the extended type area of the MaaSt.richtian St.age and showing the location of the former ENCI-HeidelbergCement Group quarry (modified from Jagt et al., 2020).
	Figure 2. ENCI-HeidelbergCement Group quarry.The northeaSt. corner of the former ENCI-HeidelbergCement Group quarry (MaaSt.richt), looking southweSt. (Spring 2019); the level with tyre tracks corresponds roughly to the lower Gronsveld Member (St. Pieter and ENCI horizons; see Fig. 3; photograph by Mart J.M. Deckers).
	Figure 3. Litholog of the lower MaaSt.richt Formation.Log (modified from Felder & Bosch, 1998), with the St. Pieter and ENCI horizons in the lower part of the Gronsveld Member. The arrow in the higher part of that unit refers to one of the more spectacular St.orm levels in the section (for details, see Jagt et al., 2019).
	Figure 4. Plaeogeographical map.ReconSt.ruction of oceans, epicontinental seas and land masses during the late Late Cretaceous (c. 75 Ma; ©2012 Colorado Plateau GeosySt.ems Inc.).
	Figure 5. Ophiomitrella. floorae n. sp., from the lower Gronsveld Member (MaaSt.richt Formation; St. Pieter and ENCI horizons) at the former ENCI-HeidelbergCement Group quarry, MaaSt.richt, the Netherlands.A–B: holotype (NHMM JJ 5104), dissociated proximal lateral arm plate in external (A) and internal (B) views; C: paratype (NHMM K 3387), articulated disc with basal arm segments in ventral view. Ophiomitrella granulosa Recent, as a close living relative of O. floorae n. sp. D–E: proximal lateral arm plate (SMNH-121224) in external (D) and internal (E) views; F–G: complete individual (MNHNEcOs22429) in dorsal view (F) and with detail of ventral disc skeleton (G). Abbreviations: AOS, adoral shield; AS, arm spine; do: dorsal; LAP, lateral arm plate; MO, muscle opening; NO, nerve opening; OS, oral shield; pr, proximal; R, ridge; T, tooth; VA, vertebral articulation; VAP, ventral arm plate. Scale bars equal 0,25 mm in A–B and D–E, and 1 mm in C and F–G. Scanning electron microscope images of Figs. F-G by Sabine St.öhr.
	Figure 6. Ophiomitrella floorae. n. sp., from the lower Gronsveld Member (MaaSt.richt Formation; St. Pieter and ENCI horizons) at the former ENCI-HeidelbergCement Group quarry, MaaSt.richt, the Netherlands. Paratype (NHMM K 3387).(A) articulated skeleton before removal of the disc and proximal arm segments for scanning electron microscopy; (B) detail of an arm in dorsal view. Abbreviations: DAP, dorsal arm plate; LAP, lateral arm plate. Scale bars equal 1 mm.

References [+] :

O'Hara, Phylogenomic resolution of the class Ophiuroidea unlocks a global microfossil record. 2014, Pubmed, Echinobase