Acanthopleura vaillantii de Rochebrune 1882

Acanthopleura vaillantii de Rochebrune, 1882 (Fig. 17) Chiton (Tonicia) sueziensis, non Reeve; Issel 1869, p. 235 (pars). Acantopleura (sic) vaillantii de Rochebrune 1882, p. 192. Acanthopleura gemmata; Ferreira 1983, p. 278, fig. 30. Acanthopleura haddoni; Vine 1986, p. 126, unnumbered figs p. 125, 126. Acanthopleura vaillantii; Ferreira 1986, p. 231, fig. 17; Kaas & Van Belle 1988, p. 123; Strack 1993, p.: 17, pl. 4, figs 3���4; Bosch et al. 1995, p. 190, fig. sp. 885; Dekker & Orlin 2000, p. 7; Slieker 2000, p. 50, fig. 24; Brooker 2003, p. 44, 153, 214, 486, figs 5.8, 6.5; Abubakr 2004, p. 73; Anseeuw & Terryn 2004, p. 14, figs 46���47; Kaas et al. 2006, p. 268, fig. 109, map 45; Dekker & Gemert 2008, p. 124; Dinapoli & Janssen 2009, p. 8, pl. 4a���c; Sadeghi & Loghmani 2010, p. 1, figs 2���3; Angeletti et al. 2018, p. 374, fig. 6, Blatterer 2019, p. 52, Fig. 3 f-g, pl. 3, fig. 6 a-e. Type material. MNHN, lectotype and paralectotype designated by Ferreira (1986). Type locality. Suez, Egypt. Material examined. Saudi Arabia, Gulf of Aqaba (Ash Shaykh Humayd): St. 3: 11 valves (1 head, width 18.5 mm, and 10 intermediate, maximum width 29 mm), Figs 17 A���C (MZB 50554); St. 6: 1 intermediate valve, width 24.5 mm (MZB 60261); St. 9: 1 intermediate valve (figured in Angeletti et al. 2018). Egypt, Shaw��r��ţ island.: St. 19: 1 intermediate valve, width 27.5 mm (MZB 60274). Description. Head valve nearly semicircular. Intermediate valves broadly rectangular to widely V-shaped, side margins rounded, apex blunt, lateral areas little or not raised, hardly marked. Tegmental sculpture often indistinguishable on account of erosion and encrustation, consists of roundish tubercles irregularly arranged, ocelli very small, abundantly distributed on end valves and more than half lateral areas of intermediate valves. Articulamentum glossy, apophyses large, rounded, connected across the sinus by a short, concave jugal plate, slit formula 10/I/ 9���10, teeth short, deeply grooved on the dorsal side, pectinate. Remarks. This is the only species of Acanthopleura known to live in the northern Red Sea, and is also the largest Red Sea chiton (reaching �� 100 mm in length). The determination of Acanthopleura species is often difficult due to their high degree of intraspecific variability, similarity between congeneric species, and frequent erosion on the dorsal parts of plates. Ferreira (1983, 1986) considered all the Red Sea specimens to belong to A. gemmata (de Blainville, 1825), while Kaas & Van Belle (1988) and Strack (1993) regarded the Red Sea, Yemen, Oman and Arabian Gulf populations as distinct from A. gemmata, A. vaillantii de Rochebrune, 1882 being the oldest available name for these. The Red Sea specimens were also determined in early publications as Chiton spiniger Sowerby, 1840 (now considered a synonym of A. gemmata) and Acanthopleura haddoni Winckworth, 1927 (Brooker 2003). Acanthopleura vaillantii inhabits the intertidal zone and is therefore an excellent sea-level indicator in paleoecological studies (Angeletti et al. 2018). However, on-land occurrences of loose plates could be misleading for geological purposes due to collection and displacement by humans rather than representing genuine ecological settings (M. Taviani, pers. observ.). Distribution. Late Pleistocene: Saudi Arabia, Gulf of Aqaba (Ash Shaykh Humayd: this study); Egypt (Hurghada: Issel 1869; Shawarit isl.: this study). Present-day: Red Sea, Yemen, Socotra Island, Oman, Iran, and the entrance of the Arabian Gulf (Kaas et al. 2006; Dinapoli & Janssen 2009; Blatterer 2019).
Published as part of Dell'Angelo, Bruno, Landau, Bernard M., Sosso, Maurizio & Taviani, Marco, 2020, Late Pleistocene Red Sea Mollusca: 1. Polyplacophora, pp. 401-449 in Zootaxa 4772 (3) on pages 428-429, DOI: 10.11646/zootaxa.4772.3.1, http://zenodo.org/record/3819654
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