Acanthochitona interglacialis, Dell’Angelo & Landau & Sosso & Taviani, 2020

Dell’Angelo, Bruno, Landau, Bernard M., Sosso, Maurizio & Taviani, Marco, 2020, Late Pleistocene Red Sea Mollusca: 1. Polyplacophora, Zootaxa 4772 (3), pp. 401-449 : 433

Acanthochitona interglacialis n. sp.

( Fig. 20 )

Type material. Holotype: MZB 50560, an intermediate valve, width 1.6 mm ( Figs 20 A–C).

Type locality. Saudi Arabia, Gulf of Aqaba , Ash Shaykh Humayd: St. 8 .

Type stage. Late Pleistocene, last interglacial MIS5e.

Etymology. The name refers to the stratigraphic occurrence of the available material (interglacial deposits).

Diagnosis. Intermediate valve pentagonal, elevated, rounded in anterior profile, posterior margin slightly concave either side of strongly protruding apex. Tegmentum sculptured with elongated, flattened pustules of variable size. Articulamentum with apophyses projecting forward, insertion plate short with one slit on each side.

Description. Intermediate valve pentagonal, elevated (H/W = 0.55), rounded in anterior profile, anterior margin strongly concave in jugal part, posterior margin slightly concave on both sides of strongly protruding apex. Tegmentum sculptured with elongated, widely-spaced, irregularly arranged, flattened pustules, of variable size, up to 100 µm in length, with up to 13 microaesthetes irregularly disposed.

Articulamentum with apophyses projecting forward, insertion plate short with short, narrow slits, one on each side.

Remarks. A single intermediate valve is present in the studied material that superficially resembles an intermediate valve of the genus Acanthochitona , but without a well developed jugal area. The jugal area is in continuity with the pleural areas and not separate, and it has the same type of sculpture formed by large granules, albeit more irregular and less evident. The elevation of the valve is an uncommon character in Acanthochitona . We therefore describe this unique intermediate valve as a new species. The attribution to the genus Acanthochitona is tentative, based on the great similarity of this valve with intermediate valves pertaining to Acanthochitona .

Other living species of Acanthochitona without a well defined jugal area are known, i.e. Acanthochitona sp. ( Sirenko 2012: 98, fig. 33) and A. lanae Sirenko & Saito, 2017 ( Sirenko & Saito 2017: fig. 30), both from Vietnam, but this could be the first report (B. Sirenko, pers. comm.) of a fossil species of Acanthochitona with this feature.

Distribution. Late Pleistocene: Saudi Arabia, Gulf of Aqaba (Ash Shaykh Humayd: this study).

Figures

FIGURE 20. Acanthochitona interglacialis n. sp. A–C. Saudi Arabia, Gulf of Aqaba, Ash Shaykh Humayd (St. 8), Late Pleistocene (last interglacial MIS5e), Holotype MZB 50560, intermediate valve, width 1.6 mm, dorsal view, detail of tegmentum surface of pleural area and frontal view. Scale bar: 100 µm (B).