Loxoconcha petasa ( Livental, 1929 )

RAUSCH, LEA, STOICA, MARIUS & LAZAREV, SERGEI, 2020, A Late Miocene - Early Pliocene Paratethyan Type Ostracod Fauna From The Denizli Basin (Sw Anatolia) And Its Palaeogeographic Implications, Acta Palaeontologica Romaniae 16 (2), pp. 3-56 : 44

Loxoconcha petasa ( Livental, 1929)

Fig. 28 a-j

1929 Loxoconcha petasus nov. sp. - Livental, p.33, pl. 1, fig. 39-41.

1978 Loxoconcha petasa Lievental- Olteanu, pl. 5, fig. 8; pl. 7, fig. 1.

1967 Loxoconcha ex. gr. petasus Livental- Agalarova, p. 110, pl. 19, fig. 1a.

1972 Loxoconcha petasus Livental- Sokač, p. 86, pl. XLVI, fig. 2-8.

1986 Loxoconcha petasa Livental- Yassini, p. 50, pl. 17, fig. 1-3.

2001 Loxoconcha petasus Livental- Tunoğlu, p. 142, pl. 1, fig. 1-3.

2013 Loxoconcha petasa Livental- Stoica et al., p. 140, pl. 2, fig 37.

2013 Loxoconcha petasa Livental- Van Baak et al., p. 124, fig. 4b, 22.

Description. The carapace is rhomboidal in lateral view and shows a coarse and irregular reticulate surface ornamentation and a distinguishable eye-spot. The ornamentation is composed of meshes of different sizes that tend to be arranged in longitudinal running rows in proximity to the ventral margin. The dorsal margin is straight and is passing smoothly onto the rounded convex anterior border as well as onto the broadly rounded posterior end at a small, rather deep depression that is creating an edge that is especially visible on the RV. Anterior and posterior pass smoothly onto the ventral margin which runs parallel and almost straight to the dorsal margin. Towards the posterior the ventral margin is recurving and slightly convex. In males the anterior end is noticeably narrower than the posterior one. Along the posterior-and anterior margin several randomly distributed cone-shaped pores are present. The ones in the posterior part tend to be higher pronounced. The marginal zone is wide and several simple marginal pore canals are present. The hinge is amphidont and represented by a crenulated bar with one tooth being present at the anterior end and two divided teeth at the posterior end of the LV. Dimension: L = 0,67 – 0,70 mm, H = 0,30 – 0,39 mm, the minimum sizes include juveniles too.

Chronostratigraphical and geographical distribution. Within the Paratethys domain L. petasa is known from the Pontian deposits of the Pannonian Basin of Yugoslavia ( Sokač, 1972), the upper Pontian (Bosphorian) of the Rîmnicu Sărat Valley in the Dacian Basin ( Stoica et al., 2013) and the Pontian from the Bădislava – Topolog area in the South Carpathian foredeep region in Romania ( Floroiu et al., 2011). Further it has been described from the Pliocene (Akchagylian and Apsheronian) of the Caspian Basin in Azerbaijan, Turkmenistan (the post-Pliocene western part of Turkmenistan), the northern Caucasus, the lower Volga Plain and in recent assemblages of the Caspian Sea ( Agalarova et al., 1961;Yassini, 1986; Sokač, 1990; Van Baak et al., 2013; Lazarev et al., 2019). This species is also known from the Eastern Black Sea region of Turkey ( Tunoğlu, 2001).

Ecology. According to the environmental preference of the genus Loxoconcha , L. petasa can be considered a shallow marine indicator ( Tunoğlu, 2001). Recent living Loxoconcha species are globally occurring in mesohaline to euryhaline and have been reported from salinities ranging from 4,5 – 13,5 ‰ in the Caspian Sea (Yassini, 1986; Gliozzi, 1999).

Figures

Fig. 28a-j Loxoconcha petasa; a LV, external view, ♂; b, g RV, external view, ♂; c LV, external view, ♀; d RV, external view, ♀; e LV, internal view, ♂; f, h RV, internal view, ♂; i Carapace, dorsal view, ♀; j Carapace, ventral view, ♀; (all specimens from section B, samples 100 m – 184,5 m).