Leptochiton abacinus

Leptochiton abacinus ( Dell’Angelo & Palazzi, 1989)

Fig. 9 View FIGURE 9

Lepidopleurus ( Leptochiton) abacinus Dell’Angelo & Palazzi, 1989, p. 79, pl. 26; Schwabe 2005, p. 89.

Leptochiton abacinus ; Dell’Angelo et al. 2007b, p. 142.

Type material. Holotype MZB 7074, intermediate valve, width 3.6 mm ( Figs 9A–E View FIGURE 9 ); Paratype BD 3828, intermediate valve, width 1.6 mm.

Type locality. Pezzo, near Villa S. Giovanni ( Calabria, Italy) .

Type stage. Upper Pleistocene, but possibly reworked from contiguous deposits of the Lower Pleistocene of bathyal facies.

Material examined. Upper Pleistocene: Pezzo ( Italy): type material and another intermediate valve ( BD 335 , Figs 9F–H View FIGURE 9 ), width 3.5 mm. Maximum width of the valves: 3.6 mm (intermediate) .

Description. Head and tail valves unknown. Intermediate valves broadly rectangular, semicarinate in anterior profile forming angle of ca 80°, highly elevated (H/W = 0.60–0.68), anterior margin concave in wide jugal area, antero-lateral corners obliquely truncated, side margins slightly rounded, posterior margin almost straight at both sides of small apex, lateral areas very raised.

Tegrnentum rough, sculptured with roundish-polygonal, separated granules, irregularly arranged, less evident in JA, forming longitudinal irregular ribs in hind zone of CA, for about half valve; LA furrowed by strong concentric growth lines in continuity with those of CA.

Articulamentum without insertion laminae, apophyses wide, semicircular.

Remarks. This species has been found only from the type locality, and the head and tail valves are not known. At the time of the original description, only the two valves designated as holotype and paratype were known. The holotype is illustrated here for the first time (only by drawings in the original description). The paratype is smaller and differs from the holotype for a lowest elevation, a less pronounced jugal angle, and in lacking the longitudinal irregular ribs in the hind zone of CA. Subsequently, another intermediate valve was found, shown here ( Figs 9F–G View FIGURE 9 ), matching to the characters of Leptochiton abacinus ( Dell’Angelo & Palazzi, 1989). The anterior profile seems a little more carinated ( Fig. 9G View FIGURE 9 ), the height/width ratio is 0.60 (vs. 0.68 of the holotype), and the angle of anterior profile is 80°, as in the holotype.

Comparisons. Leptochiton abacinus differs from all Leptochiton species discussed here, mainly because of its considerable elevation (H/W = 0.60–0.68) and for the peculiar sculpture with irregularly arranged granules, forming longitudinal irregular ribs only in the hind zone of PA for about half valve.

Distribution. Pleistocene: central Mediterranean, S. Italy: Pezzo ( Dell’Angelo & Palazzi 1989; this study).