Orbiculoidea winsnesi Gobbet, 1963

Foster, William J., Danise, Silvia & Twitchett, Richard J., 2017, A silicified Early Triassic marine assemblage from Svalbard, Journal of Systematic Palaeontology 15 (10), pp. 851-877 : 854

Orbiculoidea winsnesi Gobbet, 1963

( Fig. 2A )

1963 Orbiculoidea winsnesi Gobbett : 46, pl. 1, figs 4, 5.

Material. One dorsal valve from LD-04 ( NHMUK PI BE 3238).

Description. Shell outline is subcircular, with its length slightly greater than the width. The dorsal valve is inflated to an apex, which is located about a third of the diameter from the anterior margin. Shell smooth, except for fine concentric growth lines.

Remarks. Extant solitary discinids are sessile, epifaunal invertebrates that attach to hard surfaces with a suckerlike pedicle ( Mergl 2010). They have been attaching to shelled invertebrates since the Ordovician ( Mergl 2010), and one of the specimens described herein is attached to an ammonoid. Discinids are suspension feeders, and their co-occurrence with lingulids in laminated black shales has led some authors to interpret them as being tolerant of low-oxygen conditions (Savoy 1992; Hallam 1995; Mergl 2010).

Mode of life. Surficial, stationary, attached, suspension feeder ( Mergl 2010).

Figures

Figure 2. A, Orbiculoidea winsnesi Gobbet, 1963, NHMUK PI BE 3238, dorsal view, dorsal valve; B, Austrotindaria? canalensis (Catullo, 1846), NHMUK PI MB 1198, external view, left valve; C–G, Promyalina schamarae (Bittner, 1899), external view; C, D, NHMUK PI MB 1204; C, right valve; D, left valve. E, F, NHMUK PI MB 1203; E, right valve; F, left valve. G, NHMUK PI MB 1202, right valve. Scale bars: A, B, G = 2 mm, C–F = 1 mm.