Choneplax indica Odhner, 1919

Dell’Angelo, Bruno, Landau, Bernard M., Sosso, Maurizio & Taviani, Marco, 2020, Late Pleistocene Red Sea Mollusca: 1. Polyplacophora, Zootaxa 4772 (3), pp. 401-449 : 435-437

Choneplax indica Odhner, 1919

( Fig. 22 )

Choneplax indicus Odhner 1919, p. 40 , pl. 3, figs 44-45.

Choneplax indica ; Bergenhayn 1931, p. 3, pl. 1, figs 5–9; Kaas 1985, p. 331, 339; Kaas 1986, p. 20, figs 67–72; Kaas & Van Belle 1998, p. 95; Slieker 2000, p. 50, fig. 32; Sirenko 2003, p. 33, 35, fig. 11; Dell’Angelo et al. 2004, p. 58, pl. 6, figs 8–13; Schwabe 2004, p. 3160, figs 11–13, 17D; Sirenko 2006, fig. 8A; Dinapoli & Janssen 2009, p. 31, pl. 16 a–c; Dell’Angelo et al. 2010b, p. 40, fig. 4H; Blatterer 2019, p. 56, pl. 6, fig. 15a-l.

Type material. Holotype: SMNH 1324, indicated as syntype (fide Schwabe 2004: 3160).

Type locality. Tamatave , Madagascar .

Material examined. Saudi Arabia, Gulf of Aqaba (Ash Shaykh Humayd: this study): St. 2: 1 tail valve ( MZB 60264); St. 4: 2 intermediate valves ( MZB 60265); St. 7: 1 intermediate valve ( MZB 60266); St. 8: 37 valves (1 head, 30 intermediate and 6 tail) ( MZB 60267); St. 9: 6 valves (1 intermediate and 5 tail), Figs 22 H–I ( MZB 50564); St. 10: 2 intermediate valves ( MZB 60268). Egypt, (Hurghada): St. 12: 50 valves (3 head, 40 intermediate and 7 tail) ( BD 229): St. 13: 306 valves (15 head, 216 intermediate and 75 tail), Figs 22 A–G, 22J–L ( BD 230; MZB 50563; RGM.1356862). Egypt, Hamata: St. 18: 1 intermediate valve ( MZB 60273). Maximum width: 1.6 / 2.6 / 2.4 mm.

Description. Head valve semielliptical, apex hardly developed, sculptured with very large granules arranged in quincunx.

Intermediate valve elliptical in shape, more or less elongated, jugal area narrow, smooth, from triangular to almost rectangular, growth lines clearly visible, sculptured with granules arranged in longitudinal lines in pleurolateral areas and end without overlapping along the smooth, wedge-shaped jugum

Tail valve with mucro situated terminally, not elevated and inconspicuous, antemucronal area sculptured like intermediate valves, but jugum less wedge-shaped, postmucronal area lacking.

Tegmentum surface completely granulated, except for smooth jugal area, macroaesthetes of granules posteriorly situated and surrounded by five microaesthetes.

Articulamentum with apophyses rather large and triangular, directed laterally in intermediate valves, much shorter and closer-set in tail valve, slit formula 3/0/0, slits in head valve very short, slit rays visible in head valve only.

Remarks. A detailed description of this species was given by Schwabe (2004). Choneplax indica Odhner, 1919 is characterised by elongate, convex valves, with raised, smooth jugum and elliptical granules, sometimes coalescent, arranged in longitudinal rows diverging forward from the apex in latero-pleural areas.

Choneplax indica is the most common species found in the Hurghada localities St. 12 and St. 13 (356 valves, 31.6% of the total number of valves). The examined specimens fully agree with descriptions and figures provided by Kaas (1986), Dell’Angelo et al. (2004), Schwabe (2004) and Dinapoli & Janssen (2009). The granules are roundish, similar to those figured by Schwabe (2004: fig. 11C) in intermediate valves, a central macroaesthete is clearly visibile, whereas the microesthetes are not visible due to erosion and adherent matrix. Some intermediate valves ( Fig. 22H ) match well with the valve figured by Schwabe (2004: fig. 11B) as second intermediate valve. Leloup (1981) described two other species of Choneplax from Madagascar, C. parvus , and C. sp., both discussed at length by Kaas (1986), who considered them to represent synonyms of C. indica .

The valves of Choneplax indica resemble those of Cryptoplax sykesi in many respects. Whilst complete living specimens of both species are easily separable, it is more difficult to separate single valves. Choneplax (attributed to the family Acanthochitonidae , see Sirenko 2006 and Irisarri et al. 2014) differs from Cryptoplax (attributed to the family Cryptoplacidae ) in the strong imbrications of all the valves, and most importantly in the different characters of girdle. Sirenko (2003) suggested that the evolution of the superfamily Cryptoplacoidea (which includes three families: Acanthochitonidae , Cryptoplacidae , and Hemiarthridae ) can be connected to a reduction of the tegmentum and, as a result, a reduction of slits on the insertion plates.

This is the first fossil record of the species.

Distribution. Late Pleistocene: Saudi Arabia, Gulf of Aqaba (Ash Shaykh Humayd: this study); Egypt, (Hurghada, Hamata: this study). Present-day: Leven Bank (North of Mozambique Channel), Madagascar, Réunion, Mauritius, and Rodrigues (Mascarene Islands), Socotra island ( Dell’Angelo et al. 2010b; Blatterer 2019).

Figures

FIGURE 22. Choneplax indica Odhner, 1919. A–G, J–L. Egypt, Hurghada (St. 13), Late Pleistocene (last interglacial MIS5e). A–C. MZB 50563a, head valve, width 1.3 mm, dorsal view, detail of tegmentum surface and posterior view. D–G. MZB 50563b, intermediate valve, width 2.6 mm, dorsal view, detail of tegmentum surface of latero-pleural area, ventral and lateral views. J–L. MZB 50563c, tail valve, width 1.5 mm, dorsal, ventral and lateral views. H–I. Saudi Arabia, Gulf of Aqaba, Ash Shaykh Humayd (St. 9), Late Pleistocene (last interglacial MIS5e), MZB 50564, intermediate valve, width 1.5 mm, dorsal and lateral views. Scale bars: 100 µm (B, E).