Leptochiton freiwaldi, Dell’Angelo & Sosso & Taviani, 2024

Dell’Angelo, Bruno, Sosso, Maurizio & Taviani, Marco, 2024, A critical update of Mediterranean chitons (Mollusca: Polyplacophora) with the description of new taxa, Zootaxa 5497 (2), pp. 194-208 : 196-197

Leptochiton freiwaldi new species

( Figure 2 )

Lepidopleurus (Leptochiton) sarsi (non Kaas, 1981); Dell’Angelo & Giusti 2000, p. 54, figs 5–10.

Type material. Holotype: MZUB 60348 intermediate valve, width 3.5 mm ( Figs 2A–E ) . Paratype 1: MZUB 60349 , head valve, width 2.1 mm ( Figs 2F–G ) ; Paratype 2: MZUB 60350 tail valve, width 2.2 mm ( Figs 2H–J ) ; Paratype 3: MNHN-IM-2022-2408, intermediate valve, width 3 mm; Paratype 4: MNHN-IM-2022-2409, tail valve, width 2.7 mm ( Figs 2K–L ); Paratype 5: SMF 366408 , intermediate valve, width 2.9 mm ; Paratype 6: SMF 366409 , tail valve, width 2.7 mm .

Type locality. Western Mediterranean , Tyrrhenian Sea , Tuscan Archipelago offshore Capraia island-Capo Corso, -350/ 500 m.

Etymology. The species is named after André Freiwald for his outstanding contribution to the study of Atlantic and Mediterranean deep-sea habitats.

Material examined. Tyrrhenian Sea, offshore Capraia island-Capo Corso, Tuscan Archipelago, from trawl fishing residues at -350/ 500 m: type material and 100+ valves ( BD 248 ). Maximum width: 2.7 / 3.5 / 3.0 mm .

Diagnosis. Head valve semicircular, intermediate valves broadly rectangular, rounded, elevated, apex not evident, tail valve semicircular, mucro subcentral, not prominent. Tegmentum rough, sculptured with small elliptical granules (up to 40 µm), randomly arranged in HV, LA, PMA, roundish and more compact (up to 55–60 µm), arranged in longitudinal series in CA, AMA, each granule with 3–6 aesthetes of same size. Articulamentum without insertion laminae, apophyses small, triangular in intermediate valves, trapezoid in tail valve.

Description. Head valve semicircular, posterior margin widely V-shaped. Intermediate valves broadly rectangular (W/L = 2.43–2.85), rounded in anterior profile, elevated (H/W = 0.44–0.51), anterior margin almost straight, side margins rounded, posterior margin straight, apex not evident, lateral areas not raised. Tail valve semicircular, elevated, anterior margin slightly convex, mucro not prominent, subcentral, antemucronal slope convex, postmucronal slope slightly concave.

Tegmentum rough, space between striae of granules very reduced. HV, LA, PMA sculptured with small elliptical granules (up to 40 µm) moderately raised, with 2–3 stems in apical part, randomly arranged, faint concentric lines of growth in LA, more evident in HV, PMA. CA, AMA sculptured with granules roundish and more compact (up to 55–60 µm) arranged in longitudinal series (CA 80, AMA 60), with a regular quincuncial pattern displayed by granules of neighboring rows. Each granule with a variable number of aesthetes, up to 6 in CA and AMA, and 3 aesthetes lined up along diameter in HV, LA and PMA, all aesthetes of same size.

Articulamentum without insertion laminae, weakly developed, apophyses small, triangular, wide apart in intermediate valves, trapezoid in tail valve.

Remarks. This material was studied by Dell’Angelo & Giusti (2000), and attributed to Leptochiton sarsi (Kaas, 1981) . A more in-depth examination of both species allowed to detect some significant differences, which lead us to consider these valves as belonging to a new species.

Leptochiton freiwaldi sp. nov. is presently known only from submerged assemblages of putative glacial Pleistocene age trawled offshore Capraia island and Capo Corso in the Tyrrhenian Sea at a depth of 350/ 500 m.

Comparisons. Leptochiton freiwaldi sp. nov. differs from Leptochiton sarsi mainly by the different sculpture, with longitudinal striae of granules in CA and AMA more numerous and dense, unlike L. sarsi , which shows tegmentum rough, and space between striae of granules large.Also, the shape of the intermediate valves is different, with valves about twice as wide (W/L = 1.90–2.12) in L. sarsi , more elongated (W/L = 2.43–2.85) in L. freiwaldi sp. nov..

Distribution. Western Mediterranean, possibly from last glacial Pleistocene assemblages ( Dell’Angelo & Giusti 2000; this study).

Figures

FIGURE 2. Leptochiton freiwaldi sp. nov.; Tyrrhenian Sea: offshore Capraia island-Capo Corso, depth ca. -350/500 m. A–E. Holotype (MZUB 60348), intermediate valve, width 3.5 mm, dorsal (A) and ventral (B) views, close-up of surface ornamentation of central area (C–D), and frontal view (E). F–G. Paratype 1 (MZUB 60349), head valve, width 2.1 mm, dorsal view (F) and close-up of surface ornamentation (G). H–J. Paratype 2 (MZUB 60350), tail valve, width 2.2 mm, dorsal view (H), close-up of surface ornamentation of postmucronal area (I) and lateral view (J). K–L. Paratype 4 (MNHN-IM-2022-2409), tail valve, width 2.7 mm, dorsal view (K) and close-up of surface ornamentation of antemucronal area (L). Scale bars: 100 µm (C); 40 µm (I, L); 20 µm (G); 10 µm (D).