Ischnochiton luquei, DELL’ANGELO et al. 2024, DELL’ANGELO et al., 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 : 199-200

“ Ischnochiton ” luquei sp. nov.

( Figure 4 )

Type material. Holotype: MZUB 60343 , intermediate valve, width 2.5 mm ( Figs 4A–D ) . Paratype 1: MZUB 60344 , intermediate valve, width 2.8 mm ; Paratype 2: MZUB 60345 , intermediate valve, width 2.5 mm ; Paratype 3: MZUB 60346 , intermediate valve, width 2.8 mm ; Paratype 4: MNHN-IM-2022-2405, intermediate valve, width 3.1 mm ( Figs 4E–F ); Paratype 5: SMF 376793 , intermediate valve, width 2.8 mm ; Paratype 6: MZUB 60347 , intermediate valve, width 3 mm ( Figs 4G–H ) .

Type locality. Western Mediterranean , Tyrrhenian Sea , offshore Capraia-Capo Corso, Tuscan Archipelago, depth ca. 350/ 500 m, by fishers .

Etymology. This species is named after Angel Luque for his contribution to the study of Mediterranean and NE Atlantic molluscs.

Material examined. Offshore Capraia island-Capo Corso, -350/ 500 m: type material plus 9 intermediate valves ( BD 251 ). Maximum width: 3.4 mm .

Diagnosis. Intermediate valve broadly rectangular, semicarinate, elevated, apex well developed. Tegmentum smooth, with some weak concentric growth lines. Articulamentum with large, triangular apophyses, insertion plate short with 1 slit, a second slit ray visible near posterior margin.

Description. Head and tail valves unknown. Intermediate valve broadly rectangular (W/L = 1.72–1.96), semicarinate in anterior profile, elevated (H/W = 0.45–0.50), anterior margin convex, side margins almost straight or little rounded, posterior margin almost straight at both sides of protruding apex, lateral areas raised.

Tegmentum smooth. LA and CA with some weak concentric growth lines.

Articulamentum with large, triangular apophyses, insertion plate short with 1 slit, slit rays well visible, a second slit ray is almost always visible near posterior margin.

Remarks. “ Ischnochiton ” luquei sp. nov. is so far only known from the Tuscan Archipelago offshore Capraia island/Capo Corso at -350/ 500 m. Only intermediate valves are present.

The generic attribution is difficult; many extant species with a smooth or microgranulose tegmentum are attributed to the genera Ischnochiton Gray, 1847 , Stenosemus von Middendorff, 1847 or Lepidochitona Gray, 1821 , mainly on the basis of the soft parts (e.g. the dorsal girdle coverage). We provisionally attribute the material studied to Ischnochiton , on the basis of strong similarities to species included in this genus..

Comparisons. “ Ischnochiton “ luquei sp. nov. is superficially similar to Boreochiton ruber ( Linnaeus, 1767) , a species with an arctic-circumboreal distribution ( Kaas & Van Belle 1985; Sirenko & Dell’Angelo 2023), with whom it shares the smooth tegmentum, and from which it differs by the different shape of the intermediate valves (much more elongate in B. ruber ), and the weaker concentric growth lines, more prominent in B. ruber . Boreochiton is a genus characterized by the presence of a large fenestral gland in tail part of chitons, a characteristic feature found only in the species of the genus. Here we have loose valves, for comparisons and we prefer to adopt a conservative approach at supraspecific level.

Distribution. Western Mediterranean, possibly from last glacial Pleistocene assemblages.

Figures

FIGURE 4. “Ischnochiton” luquei sp. nov.; Tyrrhenian Sea: offshore Capraia island-Capo Corso, depth ca. 350/500 m. A–D. Holotype (MZUB 60343), intermediate valve, width 2.5 mm, dorsal view (A), close-up of surface ornamentation of central area (B), ventral (C) and frontal (D) views. E–F. Paratype 4 (MNHN-IM-2022-2405), intermediate valve, width 3.1 mm, dorsal (E) and frontal (F) views. G–H. Paratype 6 (MZUB 60347), intermediate valve, width 3 mm, dorsal (G) and ventral (H) views. Scale bar = 40 μm (B).