Ischnochiton yerburyi
Creators: name: Dell'Angelo, Bruno
name: Landau, Bernard M.
name: Sosso, Maurizio
name: Taviani, Marco
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Polyplacophora
Chitonida
Ischnochitonidae
Ischnochiton
Ischnochiton yerburyi

description: Ischnochiton yerburyi (E.A. Smith, 1891)
(Fig. 4)
Chiton (Ischnochiton) yerburyi E.A. Smith 1891, p. 420, pl. 33, fig. 6; Pilsbry 1892, p. 101, pl. 20, fig. 11.
Ischnochiton yerburyi; Leloup 1960, p. 35, fig. 5; Ferreira 1983, p. 251, figs 1–2; Strack 1993, p. 9, pl. 3, fig. 2, pl. 7, fig. 3; Bosch et al. 1995, p. 189, fig. sp. 879; Kaas & Van Belle 1998, p. 203; Dekker & Orlin 2000, p. 7; Slieker 2000, p. 46, fig. 9; Abubakr 2004, p. 73; Callea et al. 2005, p. 93; Dell’Angelo et al. 2011b, p. 25; Mohammadian 2011, p. 211, fig. p. 212; Al-Yamani et al. 2012, p. 120, pl. 83; Blatterer 2019, p. 49, pl. 2, fig. 5 a-b.
Ischnochiton yerburi (sic); Leloup 1980, p. 10; Vine 1986, p. 125.
Ischnochiton (Ischnochiton) yerburyi; Kaas 1986, p. 11, fig. 8; Anseeuw & Terryn 2004, p.7, figs 16–23, 38–39; Dinapoli & Janssen 2009, p. 23, pl. 12a–d; Hekmatara & Heidary Baladehi 2011, p. 1, fig. 2.
Ischnochiton (I.) yerburyi; Kaas & Van Belle 1988, p. 116, figs 2–7; Kaas & Van Belle 1990, p. 124, fig. 53, map 21; Dell’Angelo et al. 2004, p. 51, pl. 3, figs 4–7.
Ischnochiton (Simplischnochiton) yerburyi; Van Belle & Wranik 1991, p. 368, fig. 13; Van Belle 1994, p. 2.
Type material. BMNH 1888.4.9.345.
Type locality. Aden.
Material examined. Saudi Arabia, Gulf of Aqaba (Ash Shaykh Humayd: this study): St. 8: 8 valves (1 head and 7 intermediate) (MZB 50589); St. 9: 4 valves (1 head, 2 intermediate and 1 tail), Figs 4 G–I (MZB 50527). Egypt, Hurghada: St. 13: 6 intermediate valves (BD 181); St. 14: 14 valves (1 head, 11 intermediate and 2 tail), Figs 4 A–F (BD 182; MZB 50526; RGM.1356850); St. 14bis: 2 intermediate valves (BD 183); St. 16: 7 valves (1 head, 5 intermediate and 1 tail) (BD 184). Maximum width: 5 / 6.3 / 5.2 mm.
Description. Head valve semi-circular, posterior margin widely V-shaped, front slope straight.
Intermediate valve rectangular, L/W = 0.36–0.38, front margin sinuous, moderately elevated (H/W = 0.39– 0.44), anterior profile subcarinated, side margins rounded, posterior margin almost straight, apex hardly or not indicated, lateral areas slightly raised, poorly defined.
Tail valve semicircular, L/W = 0.58, front margin weakly convex in jugal part, mucro subcentral, not elevated, antemucronal slope slightly convex, postmucronal slope weakly concave directly behind mucro.
Tegmentum coarsely reticulated by a thimble-like sculpture, pits squarish to subromboidal, network finer on the jugal part.
Articulamentum with rounded apophyses, jugal sinus straight, relatively wide, insertion plates short, slit formula 11–13/1/11–12, slits deep, teeth inequidistant, smooth.
Remarks. A detailed description of this species was given by Kaas & Van Belle (1990). Ferreira (1983) synonymised four other nominal Ischnochiton species from the Indian Ocean with Ischnochiton yerburyi, all having in common a thimble-like sculptured tegmentum. After a thorough examination of the types, Kaas & Van Belle (1990) concluded that at least two species could be distinguished, I. yerburyi with a strong thimble-like sculpture that is apparent even on the head and tail valves, and I. sansibarensis Thiele, 1909 with a weaker net-like sculpture, in which the head and tail valves and lateral areas are evenly granulose-punctate. Other differences in the dorsal girdle scales and in the radula require further investigation (Kaas & Van Belle 1990; Anseeuw & Terryn 2004).
We attribute our material to I. yerburyi, despite the valves having a weaker sculpture and the front margin of the figured tail valve (Fig. 4G) being convex, as reported by Thiele (1909: pl. 8, fig. 27) and Kaas & Van Belle (1990: fig. 55/2) for I. sansibarensis. The tail valve figured has 12 slits in the articulamentum (Fig. 4H), which agrees with the number reported by Kaas & Van Belle for I. yerburyi (11–13, vs 8–10 for I. sansibarensis). Moreover, the sculpture of antemucronal and postmucronal areas seems similar (not granulose-punctate as in I. sansibarensis), and agrees with the tail valves figured by Anseeuw & Terryn (2004: fig. 20) and Dinapoli & Janssen (2009: pl. 12d) for I. yerburyi.
This is the first report of this species as a fossil.
Distribution. Late Pleistocene: Saudi Arabia, Gulf of Aqaba (Ash Shaykh Humayd: this study); Egypt (Hurghada: this study). Present-day: Indian Ocean, from the north-western Red Sea to the Maldives; African coast from Somalia to Zanzibar, Socotra island to Madagascar, and the Northern Red Sea to Mozambique; Arabian Sea: Pakistan to Yemen (Dinapoli & Janssen 2009; Hekmatara & Heidary Baladehi 2011; Blatterer 2019).
description: Published as part of Dell'Angelo, Bruno, Landau, Bernard M., Sosso, Maurizio & Taviani, Marco, 2020, Late Pleistocene Red Sea Mollusca: 1. Polyplacophora, pp. 401-449 in Zootaxa 4772 (3) on pages 408-409, DOI: 10.11646/zootaxa.4772.3.1, http://zenodo.org/record/3819654