Rhyssoplax canariensis (d’Orbigny, 1839)

Figs 9F–N

Chiton canariensis: d’Orbigny 1839: 99, pl. 7, figs 18–19; Gray 1854: 19; MacAndrew 1856: 117; Nierstrasz 1906: 515; Thiele 1909: 6; Lamy 1907: 151; Bergenhayn 1931: 18, pl. 1, figs 30–33, pl. 3, fig. 66; Nickles 1950: 14, fig. 3; Sourie 1954: 239, 299; Marche-Marchad 1958: 11; Leloup 1968 a: 28; Sabelli & Spada 1970: 6; Fischer 1978: 43; Altimira & Ros 1979: 9; Bernard 1984: 122, pl. 63; Poppe & Goto 1991: 60, pl. 1, fig. 12; Slieker 2000: 32, pl. 4, figs 39, 39a; Ardovini & Cossignani 2004: 18, figs p. 58. Type material: NHMUK 1854.9.28.152, 3 Syntypes (Figs 9H–J). Type locality: Canary Islands.

Chiton (Lophurus) canariensis: Shuttleworth 1853: 205 .

Chiton (Gymnoplax) canariensis: Dautzenberg 1910: 108; 1912: 80.

Chiton (Rhyssoplax) canariensis: Van Belle 1984 a: 101, pl. 3; Strack 1987: 181; Gerber et al. 1989: 22; Kaas 1991: 94; Kaas et al. 2006: 156, fig. 57 (chresonymy and synonymy); Rolán 2011: 50, figs 4I–T.

Chiton lyratus Sowerby 1840 a: fig. 126 (nom. nud.); 1840 b: 293; Reeve 1847: pl. xviii, species 110; Pilsbry 1893: 184, pl. 31, figs 35–36; Nierstrasz 1906: 515; Tomlin & Shackleford 1915: 269; Fernandes & Rolán 1993: 33. Type material: NHMUK 1979176, 2 Syntypes (Figs 9F–G). Type locality: unknown (Prince Island, West Africa, fide Reeve 1847).

Material examined: ST01: 2 specimens in alcohol, maximum length 11 mm (ZSM Mol-20080400); ST02: 5 specimens, maximum length 20 mm (Figs 9L, 9N) (BD 119 A); ST03: 38 specimens, maximum length 22 mm (Figs 9K, 9M) (BD 119 B); ST03: 1 specimen in alcohol, length 21 mm (ZSM Mol- 20071398), and 81 valves (14 head, maximum width 5 mm, 54 intermediate, maximum width 8 mm, and 13 tail, maximum width 4.2 mm) (BD 119 C, ER); ST05: 6 specimens, maximum length 13 mm (BD 119 D); ST07: 3 specimens, maximum length 26 mm (BD 119 E); ST09: 8 specimens in alcohol, maximum length 15 mm (ZSM Mol-20040494); ST09: 3 specimens in alcohol, maximum length 14 mm (ZSM Mol-20040503); ST10: 7 specimens in alcohol, maximum length 15 mm (ZSM Mol-20034143); ST10: 1 specimen in alcohol, length 6 mm (ZSM Mol-20034149); ST11: 10 valves (3 head, maximum width 3.5 mm, and 7 intermediate, maximum width 3.5 mm) (BD 119 F); PR 01: 5 specimens, maximum length 19 mm (BD 119 G); PR 02: 2 specimens, maximum length 18.5 mm (BD 119 H); PR 03: 1 specimen, maximum length 16 mm (BD 119 I); PR 04: 1 specimen in alcohol, length 26 mm (BD 119 J); PR 06: 11 specimens in alcohol, maximum length 21 mm (ZSM Mol-20040208); PR 07: 9 intermediate valves, maximum width 7.2 mm (BD 119 K) .

Distribution: Rhyssoplax canariensis is a common subtidal species, reported from the Canary Islands and western Africa, from Morocco to Angola (Kaas et al. 2006), and the São Tomé and Príncipe Islands. It does not occur in the Cape Verde and Madeira archipelagos except for one report from Porto Santo, Madeira, as a Pleistocene fossil (Gerber et al. 1989).

Comparison and remarks: Chiton lyratus is considered a synonym of Rhyssoplax canariensis, as already reported by Pilsbry (1893: 184). Syntypes of both taxa are illustrated (Figs 9F–G, 9H–J). The examination of the 100 valves found gives a slit formula of 8–9 / 1 / 10–13 vs. 8 / 1 / 7–11, reported by Kaas et al. (2006), which can be considered to be within the range of acceptable variation for a common and widely-distributed species. Only one intermediate valve with 2 slits on the right side was found, out of a total of 70 intermediate valves checked.

A unique head valve from ST03 has a shell scar due to injury, which caused the development of a new insertion plate under the older one in the articulamentum.