Goniomya literata

Goniomya literata (J. Sowerby, 1819)

(Figure 19 A–B)

1819 Mya ? literata —J. Sowerby, p. 45, pl. 224, fig. 1.

1931 Goniomya arctica nov. sp. —Sokolov & Bodylevsky, p. 76, pl. 4, fig. 8.

1934 Goniomya literata (J. Sowerby) —Arkell, p. 344, pl. 47, figs. 1–7 and references therein.? 1982 Goniomya cf. dubois Agassiz—Birkenmajer et al., pl. 43, fig. 5.

1982 Goniomya literata (Sowerby) —Fürsich, p. 98, figs. 35e, 36 c–d.

1985 Goniomya literata (Sowerby) —Bäckström & Nagy, p. 35, pl. 5, figs. 1–2 and references therein.

2011 Goniomya sp. —Hammer et al., tab. 2.

Material examined. Three internal moulds with small pieces of shell. See Appendix 1 for list of specimens.

Description. Shell small to medium, elongated, outline ovoid; no carina. Umbonal area positioned submedialy. Umbones not preserved. Ornament of up to 13 ventrally directed chevrons, with ridges and depressions between them roughly equal in size. Chevron ridges gently rounded with both ventral and dorsal slopes inclined at an equal angle. At younger growth stages tips of chevrons often blunt so whole ornament is trapezoidal or w-shaped. Line transecting tips of chevrons slightly inclined towards shell posterior. Angle between chevron limbs between 85 and 95 degrees. Chevron ornament transected by weak, concentric growth lines. Pallial line unknown.

Remarks. The oval shape of our specimens with almost equilaterally positioned beaks puts them into Goniomya literata (J. Sowerby, 1819) (e.g. Arkell 1934; Fürsich 1982). The Svalbard specimens differs from G. bicarinata Fürsich, 1982, from Greenland, which has a much longer posterior and two distinct carinae running from the umbo towards the anteroventral and posteroventral margins, respectively.

Occurrence. Seeps 3 and 9 (Upper Volgian–uppermost Ryazanian), Slottsmøya Member, Svalbard (Tab. 1). Goniomya literata is relatively wide-spread (Hallam 1976) and is known from the Middle Jurassic of England (e.g. Arkell 1934), Lithuania (Krenkel 1915), Spitsbergen (Bäckström & Nagy 1985) and the Upper Jurassic of England (Arkell 1934; Clausen & Wignall 1990), Greenland (e.g. Fürsich 1982) and Spitsbergen (Sokolov & Bodylevsky 1931). The genus Goniomya had much wider distribution and is common in many Jurassic fine-grained rocks (e.g. Trautschold 1865; Gerasimov 1955; Koshelkina 1962; Zakharov & Mesezhnikov 1974; Pugaczewska 1986).

Palaeoecology. We assume that G. literata was a deep-burrowing suspension feeder, by comparison with its extant relative Pholadomya candida J. de C. Sowerby, 1823 (Morton 1980). This species is a sluggish deep burrower, which remains stationary in the sediment with its siphons protruding towards the surface. The oblique shell ornament of Goniomya, comprising symmetrical ribs, is present among a variety of Late Palaeozoic and Mesozoic bivalves and was probably a shell reinforcement (e.g. Checa & Jiménez-Jiménez 2003).