Rhyssoplax maldivensis (E.A. Smith, 1903 )

Dell’Angelo, Bruno, Landau, Bernard M., Sosso, Maurizio & Taviani, Marco, 2020, Late Pleistocene Red Sea Mollusca: 1. Polyplacophora, Zootaxa 4772 (3), pp. 401-449 : 414-415

Rhyssoplax maldivensis (E.A. Smith, 1903)

( Fig. 8 )

Ischnochiton maldivensis E.A. Smith 1903, p. 596 , 619, pl. 36, figs 7–10.

Chiton (Rhyssoplax) maldivensis ; Van Belle & Wranik 1991, p. 374, fig. 19; Strack 1993, p. 15, pl. 4, fig. 2, pl. 7, figs 10–16; Schwabe 1997, p. 26, unnumbered figs p. 29; Kaas & Van Belle 1998, p. 118; Dekker & Orlin 2000, p. 7; Slieker 2000, p. 48, fig. 20; Anseeuw & Terryn 2004, p. 14, figs 44–45; Kaas et al. 2006, p. 170, fig. 63, maps 11, 32; Schwabe & Lozouet 2006, p. 625.

Chiton maldivensis ; Hylleberg & Kilburn 2002, p. 21; Abubakr 2004, p. 73.

Rhyssoplax maldivensis ; Dell’Angelo et al. 2010a, p. 13, figs 4G–I; Sirenko & Schwabe 2011, p. 119; Blatterer 2019, p. 52, pl. 3, fig. 8 a-f.

Rhyssoplax cf. maldivensis ; Sirenko 2012, p. 78, fig. 20 A–G; Sirenko 2016, p. 483, figs 1–3, 13B, C.

Type material. BMNH 1903.9.17.26.

Type locality. Felidu Atoll , Maldive Archipelago .

Material examined. Eritrea, Massawa (AGIP Exp., St. 21): 1 intermediate valve ( MGGC). Saudi Arabia, Gulf of Aqaba (Ash Shaykh Humayd): St. 2: 2 intermediate valves ( MZB 50597); St. 5: 2 intermediate valves ( MZB 50598); St. 7: 10 valves (2 head and 8 intermediate) ( MZB 50599); St. 8: 17 valves (15 intermediate and 2 tail) ( MZB 50600); St. 9: 11 valves (2 head, 8 intermediate and 1 tail) ( MZB 60251): St. 10: 2 intermediate valves ( MZB 60252); St. 11: 1 tail valve ( MZB 60253). Egypt (Hurghada): St. 12: 30 valves (5 head, 21 intermediate and 4 tail) ( BD 192); St. 13: 233 valves (31 head, 160 intermediate and 42 tail), Figs 8 A–I ( BD 193; MZB 50532; RGM.1356853); St. 14: 21 valves (2 head, 17 intermediate and 2 tail) ( BD 194); St. 14bis: 2 intermediate valves ( BD 195); St. 15: 1 intermediate valve ( BD 196); St. 16: 55 valves (8 head, 43 intermediate and 4 tail) ( BD 197). Egypt, Hamata: St. 18: 1 head valve ( MZB 60272). Maximum width: 3.4 / 4.5 / 3.8 mm.

Description. Head valve semicircular, posterior margin widely V-shaped, front slope slightly convex.

Intermediate valves rectangular, front margin slightly convex, highly elevated (H/W = 0.45–0.48), anterior profile rounded to subcarinated, side margins little rounded, posterior margin straight at both sides of the well defined apex, lateral areas raised.

Tail valve semi-circular, length about half the width (L/W = 0.50–0.51), front margin straight or slightly convex, posterior margin rather angular, mucro subcentral, prominent, antemucronal and postmucronal slopes almost straight.

Head valve, lateral areas of intermediate valves and postmucronal area of tail valve smooth, except for microsculpture and concentric growth lines, central areas with 5–8 longitudinal sulci at both sides of smooth jugum, innermost sulci not reaching front margin of valve.

Articulamentum with wide and rounded apophyses, jugal sinus rather narrow, provided with short, finely dentate plate, slit formula 8–10/1/10–13, teeths irregular, inequidistant, outer edge minutely denticulate, slit rays indicated, eaves narrow, porous.

Remarks. A detailed description of this species was given by Kaas et al. (2006). This species has occasionally been recorded (i.e. Leloup 1960, 1980) as Chiton (Rhyssoplax) corallinus ( Risso, 1826) , a well known Mediterranean species that has little in common with R. maldivensis (see Strack 1993; Kaas et al. 2006).

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

Distribution. Late Pleistocene: Eritrea, Massawa; Saudi Arabia, Gulf of Aqaba (Ash Shaykh Humayd); Egypt, (Hurghada, Hamata: this study). Present-day: Indian Ocean: Red Sea, Gulf of Aden, India, Sri Lanka, the Maldive Archipelago and South Vietnam ( Kaas et al. 2006; Sirenko 2016; Blatterer 2019).

Figures

FIGURE 8. Rhyssoplax maldivensis (E.A. Smith, 1903). A–I. Egypt, Hurghada (St. 13), Late Pleistocene (last interglacial MIS5e). A–C. MZB 50532a, head valve, width 2.8 mm, dorsal, ventral and lateral views. D–F. MZB 50532b, intermediate valve, width 3.2 mm, dorsal, ventral and frontal views. G–I. MZB 50532c, tail valve, width 3.8 mm, dorsal, ventral and lateral views.