Leptochiton sp.

Dell’Angelo, Bruno, Schwabe, Enrico, Gori, Sandro, Sosso, Maurizio & Bonfitto, Antonio, 2014, Chitons (Mollusca, Polyplacophora) from São Tomé and Príncipe Islands, African Invertebrates 55 (2), pp. 171-200 : 175

Leptochiton sp.

Figs 2E–H

Material examined: ST11: 2 tail valves, maximum width 2.1 mm (BD 106).

Description:

Tail valve less than semicircular ( Fig. 2E ), mucro central, somewhat swollen although not prominent, antemucronal slope slightly convex, postmucronal slope slightly concave just behind the mucro ( Fig. 2F ).

Tegmentum coarsely sculptured, with rather irregular, roundish and obliquely elevated granules, arranged in longitudinal series, obliquely directed in antemucronal area, radially in postmucronal area. About 28 series of granules in antemucronal area, 31 in postmucronal area, interrupted by thin, commarginal growth lines, more evident in the postmucronal area. Granules with a central macroaesthete, and a few microaesthetes irregularly disposed along margin.

Articulamentum without insertion plates. Apophyses small, subtriangular.

Distribution: São Tomé Island.

Comparison and remarks: This species differs from other Leptochiton species living along the West African coast.

Leptochiton denhartogi Strack, 2003 has a coarser tegmental sculpture, with regularly arranged roundish granules that are completely different from those of Leptochiton sp. (cf. Fig. 2H with Fig. 2C ).

Leptochiton odhneri ( Bergenhayn, 1931) , known from the northwestern coast of Africa, the Canary Islands, and Madeira, has a more weakly sculptured tegmentum, with granules that are arranged in quincunx on the head valve, the lateral areas of intermediate valves, and the postmucronal area of the tail valve.

The species is similar to Leptochiton serenae Dell’Angelo, Piccioli Resta & Bonfitto, 2007 from the Lower Pleistocene of southern Italy, which shows a more stressed sculpture pattern shaped by granules developed obliquely from the tegmentum, but a different tail valve shape (i.e. the anteriorly located mucro and the wider, trapezoidal apophyses).

The scarcity of material does not permit us to attribute it to a known species, so it is preferable to leave the identification as Leptochiton sp. until such time as more material becomes available, ideally complete specimens.

Order Chitonida Thiele, 1909

Suborder Chitonina Thiele, 1909

Family Ischnochitonidae Dall, 1889

Genus Ischnochiton Gray, 1847

Ischnochiton: Gray 1847 a: 126 . Type species: Chiton textilis Gray, 1828 , by subsequent designation (Gray 1847 b: 168).

For synonymy, see Kaas & Van Belle (1990).

Distribution: Worldwide, widespread in all seas, except for the northern Atlantic and Arctic Oceans. Eocene – Recent.

Figures

Fig. 2. (A–D) Leptochiton denhartogi Strack, 2003, São Tomé Island, ST03, intermediate valve: (A–B) dorsal and frontal views, (C–D) detail of the sculpture of the tegmentum, close-ups of granules with aesthetes in different views; (E–H) Leptochiton sp., São Tomé Island, ST11, tail valve: (E–F) dorsal and lateral views, (G–H) detail of the sculpture of antemucronal and postmucronal areas, respectively; (I–K) Ischnochiton cf. rissoi (Payraudeau, 1826), São Tomé Island, specimen from ST06: (I) dorsal view, (J) dorsal girdle scales, (K) detail of the intermediate and tail valves; (L–Q) Ischnochiton sp., SãoTomé Island, specimen from ST06:(L–M) dorsal and lateral views,(N) detail of thehead and the first intermediate valves, (O–P) detail of the sculpture of central and lateral areas, respectively, (Q) dorsal girdle scales.Scale bars = 1 mm (B); 800 μm (I); 600 μm (A); 500 μm (E); 400 μm (L, M); 300 μm (F, K); 200 μm (N); 100 μm (J); 60 μm (G, H); 50 μm (D); 40 μm (C); 30 μm (P); 20 μm (O, Q).