Leptochiton nierstraszi ( Leloup, 1981 )

Dell’Angelo, Bruno, Landau, Bernard M., Sosso, Maurizio & Taviani, Marco, 2020, Late Pleistocene Red Sea Mollusca: 1. Polyplacophora, Zootaxa 4772 (3), pp. 401-449 : 404-406

Leptochiton nierstraszi ( Leloup, 1981)

( Fig. 2 )

Lepidopleurus (Pilsbryella) nierstraszi Leloup 1981, p. 27 , fig. 13, pl. 2, fig. 1.

Leptochiton (L.) nierstraszi ; Kaas & Van Belle 1985a, p. 130, fig. 58, map 45; Kaas 1986, p. 9. Leptochiton nierstraszi ; Strack 1993, p. 3, pl. 1, fig. 1, pl. 7, figs 1–2; Kaas & Van Belle 1998, p. 130; Dekker & Orlin 2000, p. 7; Slieker 2000, p. 46, pl. 11, fig. 1; Anseeuw & Terryn 2004, p. 22; Sirenko 2013, p. 40; Sirenko 2014, p. 65; Blatterer 2019, p. 49, pl. 1, fig. 1 a-d.

Lepidopleurus (Leptochiton) nierstraszi ; Dell’Angelo et al. 2004, p. 49, pl. 1, figs 1–9.

Type material. Holotype IRSN, IG 26.374.

Type locality. Madagascar (= Malagasia), reef off Tuléar .

Material examined. Saudi Arabia, Gulf of Aqaba (Ash Shaykh Humayd): St. 8: 3 valves (1 head and 2 intermediate) ( MZB 50588). Egypt (Hurghada): St. 13: 10 valves (1 head, 8 intermediate and 1 tail), Figs 2 A–L ( BD 179; MZB 50523; RGM.1356849). Maximum width: 1.8 / 2.3 / 1.8 mm.

Description. Head valve semicircular, posterior margin widely V-shaped, with rounded notch at apex, front slope straight, tegmentum sculptured with rather large, strongly pronounced, roundish pustules quincuncially arranged.

Intermediate valves broadly rectangular, about three times as wide as long (L/W = 0.38), front margin almost straight, moderately elevated (H/W = 0.38), anterior profile rounded to subcarinated, side margins rounded, posterior margin almost straight, apex inconspicuous, lateral areas not very raised.

Tail valve semielliptical, L/W = 0.48, front margin slightly convex, mucro well defined, in anterior position, antemucronal slope strongly convex, postmucronal slope concave.

Tegmentum of all valves sculptured with rather large, strongly pronounced, well separated roundish granules quincuncially arranged, diameter 43–57 µm in central area of intermediate valves ( Fig. 2F ), with large central macroaesthete, rough interstices; granules along posterior and side margins of intermediate valves very elevated, indenting sutures.

Articulamentum with small, triangular apophyses, wider in tail valve.

Remarks. Detailed descriptions of this species were given by Kaas & Van Belle (1985a) and Dell’Angelo et al. (2004). Leptochiton nierstraszi ( Leloup, 1981) is characterised by the tegmentum covered by widely separated and elevated, subequal granules, arranged in quincunx. Dell’Angelo et al. (2004: pl. 1, figs 1–9) illustrated the tegmentum sculpture of valves of extant specimens from Tuléar ( Madagascar), showing a central macroaesthete and 1–4 microaesthetes around the granule. The central macroaesthete is clearly seen in the study material ( Fig. 2F ), the microaesthetes are not visible as the tegmentum characteristics are partially obscured by matrix (compare Fig. 2F to pl. 1, fig. 4 in Dell’Angelo et al. 2004). The other valve characters agree with those of Leptochiton nierstraszi .

In the Red Sea, this elusive species is known only from loose valves at Hurghada, Egypt ( Strack 1993).

This is the first fossil record of this species.

Distribution. Late Pleistocene (this study): Saudi Arabia, Gulf of Aqaba (Ash Shaykh Humayd); Egypt (Hurghada). Present-day: Indian Ocean: Madagascar, Réunion and the Red Sea ( Strack 1993; Dell’Angelo et al. 2004; Blatterer 2019).

Figures

FIGURE 2. Leptochiton nierstraszi (Leloup, 1981), Egypt, Hurghada (St. 13), Late Pleistocene (last interglacial MIS5e). A–D. MZB 50523a, head valve, width 1.8 mm, dorsal, ventral, lateral and posterior views. E–H. MZB 50523b, intermediate valve, width 2.3 mm: E. Dorsal view; F. Detail of tegmentum surface of central area; G–H. Ventral and frontal views. I–L. MZB 50523c, tail valve, width 1.8 mm, dorsal, ventral, lateral and posterior views. Scale bar: 100 µm (F).