Lucilina aqabaensis, 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 : 423

Lucilina aqabaensis n. sp.

( Fig. 13 )

Type material. Holotype: MZB 50545, a tail valve, St. 9, width 6.5 mm ( Figs 13 A–F).

Type locality. Gulf of Aqaba , Saudi Arabia (Ash Shaykh Humayd: this study): St. 9 .

Type stage. Late Pleistocene, last interglacial MIS5e.

Etymology. The name refers to the Gulf of Aqaba, source of the material here described.

Diagnosis. Tail valve semioval, mucro posterior, obtuse, antemucronal slope slightly convex, postmucronal slope perpendicular. Tegmentum finely granulose, antemucronal and postmucronal areas with concentric growth lines, characterised by the presence of groups of fused granules, irregularly arranged in concentric striae. Articulamentum white, apophyses well developed, jugal sinus wide, 10 slits, teeth slightly forwardly directed, finely grooved on upper side.

Description. Tail valve semioval, length less than half width (L/W = 0.42), front margin straight, hind margin angularly rounded, mucro posterior, obtuse, antemucronal slope slightly convex, postmucronal slope perpendicular.

Tegmentum finely granulose, roundish granules irregularly dispersed, extending over entire surface of valve, both antemucronal and postmucronal areas with concentric growth lines, characterised by the presence of groups of fused granules, more frequent and larger in postmucronal area along hind margin, giving the impression of being irregularly arranged in concentric striae. Roundish granules small and close-set, diameter ca 48–60 µm, with 1 large central macroaesthete and up to 10 microaesthetes along margin.

Articulamentum white, apophyses well developed, jugal sinus wide, provided with a short plate, 10 slits, slit rays not indicated, teeth relatively long, slightly forwardly directed, all teeth finely grooved on upper side, denticulated on outer edge, eaves narrow, solid.

Remarks. We assign this unique tail valve to the genus Lucilina based on the presence of having grooved teeth on the articulamentum (and not a callus as in the genus Onithochiton Gray, 1847 ), and having the mucro subterminal (and not subcentral as in the genus Tonicia Gray, 1847 ) ( Kaas et al. 2006: 294). We did not observe the presence of ocelli in the postmucronal area.

The characters of this single tail valve are so distinctive that they warrant description as a new species. The peculiar granulose sculpture of this species is different from that of other Lucilina species known from the Red Sea (including those described herein), and Indian Ocean ( Kaas et al. 2006).

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

Figures

FIGURE 13. Lucilina aqabaensis n. sp. A–F. Saudi Arabia, Gulf of Aqaba, Ash Shaykh Humayd (St. 9), Late Pleistocene (last interglacial MIS5e), Holotype, MZB 50545, tail valve, width 6.5 mm, dorsal view (in two different positions of the valve), detail of tegmentum surface of antemucronal area, ventral, lateral and posterior views. Scale bar: 100 µm (C).