Acanthochitona mastalleri Strack, 1989

Dell’Angelo, Bruno, Landau, Bernard M., Sosso, Maurizio & Taviani, Marco, 2020, Late Pleistocene Red Sea Mollusca: 1. Polyplacophora, Zootaxa 4772 (3), pp. 401-449 : 431-433

Acanthochitona mastalleri Strack, 1989

( Fig. 19 )

Acanthochiton mastalleri Strack 1989, p. 169 , textfig. 1, pls. 19, 20; Strack 1993, p. 25, pl. 5, fig. 7; Schwabe 1997, p. 28, unnumbered figs at p. 30; Kaas & Van Belle 1998, p. 119; Dekker & Orlin 2000, p. 7; Slieker 2000, p. 52, fig. 36; Anseeuw & Terryn 2004, p. 20, figs 58–59; Dell’Angelo et al. 2010a, p. 20; Blatterer 2019, p. 56, pl. 5, fig. 12 a-f.

Type material. Holotype: ZMA Moll. 388029, a specimen preserved in ethanol from Merlin Point , Hurghada, Egypt . Paratypes: many specimens in several institutions ( Strack 1989).

Type locality. Merlin Point , 4 km South of Hurghada, Egypt .

Material examined. Saudi Arabia, Gulf of Aqaba (Ash Shaykh Humayd: this study): St. 8: 2 tail valves, Figs 19 G-I ( MZB 50558); St. 9: 2 valves (1 head and 1 tail), Figs 19 A–B, 19E–F ( MZB 50557). Egypt, Hurghada: St. 13: 6 valves (5 intermediate and 1 tail) ( BD 225); St. 14: 4 valves (1 head and 3 intermediate), Figs 19 C–D ( BD 226; MZB 50559); St. 14bis: 1 intermediate valve ( BD 227); St. 16: 2 intermediate valves ( BD 228). Maximum width: 3.7 / 3.9 / 3.2 mm.

Description. Head valve semicircular.

Intermediate valve wing-shaped, posterior margin concave on both sides of well developed apex, jugal area raised, narrow, striated, sharply separated from lateropleural areas, anterior end of jugum protruding sinus, lateropleural areas much reduced, their front margins deeply concave.

Tail valve broad, antemucronal area reduced as in intermediate valves, mucro subcentral, prominent, antemucronal and postmucronal slopes almost straight, forming angle of 134–141°.

Tegmentum densely covered with irregular, more or less oval, flat topped granules, except in jugal area,

Articulamentum with apophyses extraordinarily large, insertion plates well developed, strongly protruding on intermediate valves, expanded and completely surrounding tail valve, except for jugal margin, slit formula 5/1/2.

Remarks. Detailed descriptions of this species were given by Strack (1989) and Anseeuw & Terryn (2004). Acanthochitona mastalleri Strack, 1989 is characterised by the tegmentum reduced in lateropleural areas, with markedly concave anterolateral margins, sculptured with irregular, more or less oval, flat-topped granules, and by a very wide girdle, partially extending over the valves.

Our valves agree with the description and figures of the valves given by Strack (1989), but with slight differences in the shape of the tail valves ( Figs19E, G ): they are less elongate than the valve figured by Strack (1989: fig. 4), and also the granules seem more irregular roundish, less elongate. Notwithstanding these slight differences, we consider our valves conspecific with Acanthochitona mastalleri .

This is the first report of this species as a fossil.

Distribution. Late Pleistocene: Saudi Arabia, Gulf of Aqaba (Ash Shaykh Humayd: this study); Egypt, Hurghada (this study). Present-day: Indian Ocean: Red Sea, Oman and Kenya ( Anseeuw & Terryn 2004; Blatterer 2019).

Figures

FIGURE 19. Acanthochitona mastalleri Strack, 1989. A–B, E–I. Saudi Arabia, Gulf of Aqaba, Ash Shaykh Humayd, Late Pleistocene (last interglacial MIS5e). A–B. MZB 50557a, head valve (St. 9), width 3.3 mm, dorsal and lateral views. E–F. MZB 50557b, tail valve (St. 9), width 3.1 mm, dorsal and lateral views. G–I. MZB 50558, tail valve (St. 8), width 3.2 mm, dorsal, ventral and lateral views. C–D. Egypt, Hurghada (St. 14), Late Pleistocene (last interglacial MIS5e), MZB 50559, intermediate valve, width 3.9 mm, dorsal and ventral views.