Cryptoplax sykesi Thiele, 1909

Dell’Angelo, Bruno, Landau, Bernard M., Sosso, Maurizio & Taviani, Marco, 2020, Late Pleistocene Red Sea Mollusca: 1. Polyplacophora, Zootaxa 4772 (3), pp. 401-449 : 437-439

Cryptoplax sykesi Thiele, 1909

( Fig. 23 )

Cryptoplax sp. cf. C. striatus ; Sykes 1900, p. 164, figs 2–5.

Cryptoplax striatus ; Sykes 1907, p. 33.

Cryptoplax sykesi Thiele 1909, p. 53 , pl.6, figs 83–86 (nom. nov. x Cryptoplax striatus ); Ferreira 1983, p. 287, fig. 33; Strack 1993, p. 27, pl. 5, fig. 9; Kilias 1995, p. 169; Anseeuw & Terryn 2004, p. 16, fig. 55; Dinapoli & Janssen 2009, p. 36, pl. 19a–b; Blatterer 2019, p. 56, pl. 6, fig. 17a-f.

Criptoplax (sic) striatus ; Selli 1944, p. 6.

Cryptoplax erythraeus Selli 1973, p. 260 , pl. 11, figs 8–9.

Cryptoplax enigmaticus Leloup 1980, p. 7 , pl.1, figs 1–2; pl.2, fig.1; Ferreira 1983, p. 289 (fide Ferreira 1983).

Non Cryptoplax sykesi ; Leloup 1940, p. 9, fig. 3, pl. 2, figs 1–2; Kaas 1986, p. 21, figs 73–81; Dell’Angelo et al. 2004, p. 60, pl. 6, figs 14–15; Dell’Angelo et al. 2010a, p. 32, figs 11M–O.

? (reported as Cryptoplax sykesi without description or figures); Leloup 1952, p. 53; Kaas 1985, p. 333; Kaas 1996, p. 373; Slieker 2000, p. 50, pl.13, fig.31; Ghobashy & Kotb 2002, p. 6.

? (reported as Cryptoplax striatus without description or figures); Leloup 1981, p. 21.

Type material. ZMHU, ZMB Moll 102.074 ( Fig. 23B ).

Type locality. Red Sea, “Gimsah-Bay” ( Kilias 1995) .

Material examined. Eritrea, Massawa North, Abd-el-Cader ( St. 20): 2 tail valves, described and illustrated by Selli (1973: pl. 11, figs 8–9), deposited at MGGC, with the indication “Massaua E” on the label ( Fig. 23A ) . Eritrea, Massawa South ( St. 21): 2 valves (1 intermediate and 1 tail), Figs 23 C–D ( MZB 00930) . Jordan, Aqaba, Yamanie ( St. 1): 3 intermediate valves ( MZB 60269) . Saudi Arabia, Gulf of Aqaba (Ash Shaykh Humayd): St. 8: 4 valves (3 intermediate and 1 tail), Figs 23 H–I ( MZB 50566) ; St. 9: 6 valves (5 intermediate and 1 tail) ( MZB 60270) . Egypt (Hurghada): St. 13: 16 valves (10 intermediate and 6 tail), Figs 23 E–G, 23J–O ( BD 231 ; MZB 50565; RGM.1356863). Maximum width: -/3/ 1.2 mm .

Description. Intermediate valves elliptical in shape, more or less elongated, jugal area narrow, smooth, almost rectangular, only slightly reduced near apex, growth lines clearly visible, latero-pleural areas sculptured with 5–6 longitudinal striae of irregular roundish granules starting from apex running parallel to jugal area.

Tail valve with mucro situated terminally, not elevated, inconspicuous, jugal area narrow and smooth, almost rectangular, growth lines clearly visible, antemucronal area sculptured like intermediate valves, postmucronal area lacking.

Tegmentum surface completely granulated, except for smooth jugal area, granules more irregular, often coalescing into longitudinal riblets, on each side of jugum.

Articulamentum strongly developed, intermediate and tail valves with elongate apophyses, slit formula -/0/0.

Remarks. The identification of Cryptoplax sykesi has presented some problems in past years. Specimens of Cryptoplax from east Africa were identified at first by Sykes (1900, 1907) as C. striata ( Lamarck, 1819) , a species originally described from Australian waters. Thiele (1909), based on a specimen from the Red Sea, pointed out specific differences in the shape of the tail valve, the jugal area and girdle elements, and proposed the name C. sykesi for his and Sykes’ (1907) specimens. Thiele (1909) described the sculpture of the latero-pleural areas as clearly granulose (“ The jugal field is smooth, the lateral fields with granules, which are more or less orientated in longitudinal lines ”), even if this is not evident in his figures ( Thiele 1909: figs 83–85, the sculpture seems more as longitudinal riblets than granulose), however the granulose sculpture is confirmed by the figure of the fourth valve of the lectotype deposited at ZMHU ( Fig. 23B ).

Subsequently, some authors have described and illustrated specimens identified as Cryptoplax sykesi with a sculpture of the latero-pleural areas characterised by longitudinal riblets, broken up into granules only near the apex area, e.g. Leloup (1940: 9, fig. 3, pl. 2, figs 1–2) for specimens from Vietnam; Kaas (1986: 21, figs 73–81) and Dell’Angelo et al. (2004: 60, pl. 6, figs 14–15) for specimens from Madagascar; Dell’Angelo et al. (2010b: 32, figs 11M–O) for specimens from the Maldive Islands. These specimens might represent a distinct species (H. Saito, pers. com.) for which the correct identification needs further study, which is beyond the scope of this work.

The two valves from Massawa reported by Selli (1973) as Cryptoplax sykesi clearly show a granulose sculpture. Selli described the two valves as intermediate [but some lines below: “ Quasi certamente rappresentano le valve 7 e 8 ” (Almost certainly they represent the valves vii and viii)]. On further examination, they are two tail valves, as can be seen by the different structure of the articulamentum (e.g. see the lateral view of an intermediate and tail valves of Cryptoplax weinlandi Šulc, 1934 from the Miocene of North Italy in Dell’Angelo et al. 2016: pl. 7, figs 20, 23, respectively). Selli (1973) thought that his valves with a granulose sculpture could be different from those of Cryptoplax sykesi with longitudinal riblets, and therefore proposed (in note) the name Cryptoplax erythraeus n. sp. for his valves. Since the attribution of Selli’s (1973) material to Cryptoplax sykesi is correct, the taxon Cryptoplax erythraeus must be considered a subjective synonym.

Selli’s material comes from the site of “Massawa Nord” (Abd-el-Cader peninsula, about. 2 km North of Massawa), and is stored at MGGC, but with the museum label states “Massaua E” ( Fig. 23D ). The available material consists of two valves in poor conditions of preservation (intermediate and tail) from the Agip expedition (ex Selli 1973) from “Massawa South” (near the lighthouse in the eastern part of the islet on which stands the city of Massawa).

In the study material at hand, the striae of granules are variable, with the granules more regular in some valves ( Figs 23H, J ) or coalescent in some tracts, giving the impression of riblets ( Fig. 23 E–G). This sculpture is similar to that of Cryptoplax enigmaticus Leloup, 1980 , a species described from the Red Sea ( Israel, Eilat) (see Leloup 1980: pl. 1, fig. 1). This species was discussed by Ferreira (1983: 289), who considered the specimens to be juvenile specimens of C. sykesi .

The valves of Cryptoplax sykesi resemble those of Choneplax indica in many respects, but complete living specimens of both species are easily separable. However, it is more difficult to separate single valves (see above, under the discussion of Choneplax indica ).

Distribution. Late Pleistocene: Eritrea, Massawa North (Abd-el-Cader), and Massawa South; Jordan, Aqaba (Yamanie); Saudi Arabia, Gulf of Aqaba (Ash Shaykh Humayd: this study); Egypt, (Hurghada) ( Selli 1944, 1973; this study). Present-day: Western Indian Ocean from the northern Red Sea to South Africa, Yemen and Socotra Island ( Strack 1993; Dinapoli & Janssen 2009; Blatterer 2019).

Figures

FIGURE 23. Cryptoplax sykesi Thiele, 1909 A. Erythrea, Massawa North, Abd-el-Cader, 2 tail valves figured by Selli (1973: pl. 11, figs 8-9). B. ZMHU, ZMB Moll 102.074., Lectotype, fourth valve, Red Sea, “Gimsah-Bay”, dorsal view. C–D. Erythrea, Massawa South (AGIP Exp.), MZB 000930. C. Intermediate valve, width 1.6 mm, dorsal view. D. Original label. E–G, J–O. Egypt, Hurghada (St. 13), Late Pleistocene (last interglacial MIS5e). E–G. 50565a, intermediate valve, width 3 mm, dorsal view, detail of tegmentum surface and lateral view. J–K. 50565b, intermediate valve, width 3 mm, dorsal and lateral views. L–O. 50565c, tail valve, width 2.4 mm, dorsal view, detail of tegmentum surface of latero-pleural area, ventral and lateral views. H–I. Saudi Arabia, Gulf of Aqaba, Ash Shaykh Humayd (St. 8), Late Pleistocene (last interglacial MIS5e), MZB 50566, intermediate valve, width 2.5 mm, dorsal and ventral views. Scale bar: 100 µm (F, M).