Rhyssoplax affinis ( Issel, 1869 )

Dell’Angelo, Bruno, Landau, Bernard M., Sosso, Maurizio & Taviani, Marco, 2020, Late Pleistocene Red Sea Mollusca: 1. Polyplacophora, Zootaxa 4772 (3), pp. 401-449 : 412-414

Rhyssoplax affinis ( Issel, 1869)

( Fig. 7 )

Chiton affinis Issel 1869, p. 234 ; Sykes 1907, p. 34; Pallary 1926, p. 30, pl. 4, figs 8–9 (ex Savigny 1817: pl. 3, figs 8–9); Moazzo 1939, p. 217; Yaron 1973, p. 15; Bouchet & Danrigal 1982, p. 11, fig. 51; Dekker & Orlin 2000, p. 7; Abubakr 2004, p. 73; Dekker & Gemert 2008, p. 124.

Chiton (Clathropleura) affinis ; Thiele 1909, p. 91, pl. 9, figs 41–44.

Chiton olivaceus Spengler var. affinis ; Leloup, 1952, p. 27, text-fig. 11, pl. 4, fig. 4; Leloup 1960, p. 36; Vine 1986, p. 125, unnumbered fig. p. 125.

Rhyssoplax affinis ; Ferreira 1983, p. 268, figs 22, 24; Blatterer 2019, p. 52, pl. 3, fig. 7 a–s.

Chiton (Rhyssoplax) affinis ; Kaas & Van Belle 1988, p. 122, figs 34–40; Van Belle & Wranik 1991, p. 372, fig. 18; Van Belle 1994, p. 6; Bosch et a l. 1995, p. 190, fig. sp. 884; Kaas 1996, p. 371; Schwabe 1997, p. 26, unnumbered figs at p. 27; Kaas & Van Belle 1998, p. 14; Anseeuw & Terryn 2004, p. 11, figs 5, 42–43; Kaas et al. 2006, p. 165, fig. 61, map 30; Di Napoli & Janssen 2009, p. 15, pl. 8a–d; Schwabe 2010, figs 1A, 2A, 5A–B; Mohammadian 2011, p. 211.

Type material. Lectotype MNHN in Savigny Collection, designated by Ferreira (1983: 268), as illustrated in Bouchet & Danrigal (1982: fig. 51).

Type locality. Gulf of Suez.

Material examined. Jordan, Aqaba (Yamanie) (St. 1): 2 intermediate valves ( MZB 50592). Saudi Arabia, Gulf of Aqaba (Ash Shaykh Humayd): St. 2: 1 intermediate valve ( MZB 50593); St. 7: 1 intermediate valve ( MZB 50594); St. 8: 10 intermediate valves ( MZB 50595); St. 9: 6 valves (1 head, 4 intermediate and 1 tail) ( MZB 50596). Egypt (Hurghada): St. 13: 48 valves (3 head, 36 intermediate and 9 tail), Figs 7 G–I ( BD 187; MZB 50531); St. 14: 106 valves (10 head, 90 intermediate and 6 tail), Figs 7 A–F ( BD 188; MZB 50530); RGM.1356852); St. 14bis: 4 valves (3 intermediate and 1 tail) ( BD 189); St. 15: 3 valves (2 intermediate and 1 tail) ( BD 190); St. 16: 59 valves (12 head, 36 intermediate and 11 tail) ( BD 191). Maximum width: 4 / 7.1 / 4 mm.

Description. Head valve semi-circular, posterior margin widely V-shaped, front slope slightly convex, tegmentum sculptured with 13–14 strong radial ribs, some bifurcating, interstices pitted.

Intermediate valve rectangular, L/W = 0.34–0.42, front margin sinuous, moderately to highly elevated (H/W = 0.42–0.47), anterior profile carinated, side margins short, weakly bilobed, posterior margin straight at both sides of well defined apex, lateral areas clearly defined, sculptured like head valve, 2 radial ribs separated by pitted interstices, pleural areas with ca 10 longitudinal, slightly forwardly converging grooves, innermost not reaching anterior margin of valve, interspaces somewhat broader, smooth, jugal area narrow, smooth.

Tail valve semi-circular, length more than half the width (L/W = 0.58–0.60), front margin slightly convex, posterior margin lobate, mucro well defined, subcentral, prominent, antemucronal slope almost straight or slightly convex, postmucronal slope slightly convex, antemucronal area sculptured like central area of intermediate valve, postmucronal area with sculpture like head valve.

Articulamentum with apophyses wide, short, connected across the shallow sinus by short, denticulated jugal plate, insertion plates short, slit formula 8/1/10–13, teeth inequidistant, irregular, finely striated on the upper side, slit rays not indicated.

Remarks. Issel´s original description (1869) has subsequently been revised by several authors ( Leloup 1952; Ferreira 1983; Kaas et al. 2006). Rhyssoplax affinis has been confused with the Mediterranean R. olivaceus ( Spengler, 1797) by authors following Cooke (1885). The controversy, summarized by Leloup (1952), was resolved by Yaron (1973), who demonstrated consistent morphological differences between the two species. This is the first report of this species as a fossil.

Distribution. Late Pleistocene: Jordan, Aqaba (Yamanie); Saudi Arabia, Gulf of Aqaba (Ash Shaykh Humayd); Egypt (Hurghada: this study). Present-day: Indian Ocean: Red Sea, Gulf of Suez, Yemen, Socotra Island, Gulf of Oman, the Arabian Gulf, Seychelles and Somalia ( Kaas et al. 2006; Di Napoli & Janssen 2009; Blatterer 2019).

Figures

FIGURE 7. Rhyssoplax affinis (Issel, 1869). A–I. Egypt, Hurghada, Late Pleistocene (last interglacial MIS5e). A–C. MZB 50530a, head valve (St. 14), width 3.6 mm, dorsal, ventral and lateral views. D–F. MZB 50530b, intermediate valve (St. 14), width 5.7 mm, dorsal, ventral and frontal views. G–I. MZB 50531, tail valve (St. 13), width 2.5 mm, dorsal, ventral and lateral views.