Acanthochitona barbarae, 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 : 200-201

Acanthochitona barbarae new species

( Figure 5 )

Type material. Holotype: MZUB 60341 , intermediate valve, width 3.4 mm ( Figs 5A–D ) ; Paratype 1: MZUB 60342 , tail valve, width 3.8 mm ( Figs 5E–G ) ; Paratype 2: MNHN-IM-2022-2407, intermediate valve, fragmented ( Fig. 5H ).

Type locality. Western Mediterranean, Tyrrhenian Sea , Sardinia .

Etymology. This species is named after Barbara Gualandi who participated with M.T. in research on marine habitats in the Tyrrhenian Sea and to the collecting at the type locality.

Material examined. Western Mediterranean , Tyrrhenian Sea : S. Lucia (Nuoro province, Sardinia): type material; Tunisia, Kélibia (leg. P. Quadri), one tail valve ( Figs 5I–L ) (lost after SEM photographing). Maximum width 4.2 mm .

Diagnosis. Intermediate valves broadly rectangular, semicarinate, elevated, apex well developed. Whole tegmentum (except JA) sculptured with large and well separated granules of variable size, rounded but truncated by a straight line, elevated, JA finely longitudinally striated and crossed by marked growth lines, each granule with a single subcentral megalaesthete and many micraesthetes. Articulamentum well developed, apophyses strongly protruding, expanded and completely surrounding tail valve, slit formula - / 1 / 2.

Description. Head valve unknown. Intermediate valves broadly rectangular, WT/LT = 1.34, elevated (H/W = 0.38), semicarinate in anterior profile, anterior margin straight between apophyses, lateral margins whose partly straight and partly rounded profile gives the valve a nearly pentagonal shape, posterior margin almost straight on both sides of pronounced apex, jugal area triangular, much raised. Tail valve circular, WT/LT = 1.07, very elevated, jugal area raised, mucro well evident in subcentral position, antemucronal slope straight, postmucronal slope slightly concave just behind mucro.

Whole tegmentum (except JA) sculptured with large and well separated granules, rounded but truncated by a straight line, elevated, with flat surface, jugal area finely longitudinally striated and crossed by marked growth lines, pectinated in upper edge; granules of variable size, with a single subcentral located megalaesthete and many micraesthetes, mainly grouped near straight line of granules.

Articulamentum well developed, expanded and completely surrounding tail valve, except for jugal margin, apophyses quadrangular and strongly protruding, delimiting a wide jugal sinus, slit formula - / 1 / 2.

Remarks. Acanthochitona barbarae sp. nov. is only known by a few valves from two localities in the central Mediterranean Sea (Sardinia and Tunisia). The valves from Sardinia have the granules rather eroded, the shape seem polygonal, in some cases almost triangular, but the straight line is visible in some better preserved granules, e.g. see PMA in Fig. 5E . It has been hypothesised that A. crinita could represent a «waste basket» containing, in fact, various taxa of still uncertain classification ( Vončina et al. 2023). Their biomolecular research seems to indicate this possibility for two taxa from Croatian waters. Our own study lends support to this view, although only based at present on shell morphological evidence.

Comparisons. The tegmental granules have a particular shape, different from that typical of the other Acanthochitona species known from the Mediterranean, granules small, packed, roundish in A. fascicularis ( Linnaeus, 1767) , granules oval or drop-shaped in A. crinita ( Pennant, 1777) , A. oblonga Leloup, 1981 and A. pilosa Schmidt-Petersen, Schwabe & Haszprunar, 2015 ( Schmidt-Petersen et al. 2015).

Distribution. Western Mediterranean, Sardinia and Tunisia.

Figures

FIGURE 5. Acanthochitona barbarae sp. nov. A–H. Tyrrhenian Sea: S. Lucia (Nuoro, Sardinia): A–D. Holotype (MZUB 60341), intermediate valve, width 3.4 mm, dorsal (A), ventral (B) and frontal (C) views, and close-up of surface ornamentation (D); E–G. Paratype 1 (MZUB 60342), tail valve, width 3.8 mm, dorsal (E) and lateral (F) views, and close-up of surface ornamentation (G); H. Paratype 2 (MNHN-IM-2022-2407), intermediate valve, width 4.2 mm, dorsal view. I–L. Tunisia, Keubia, tail valve, width 2.7 mm, dorsal view (I), and close-up of surface ornamentation in dorsal (J, K) and lateral (L) views. Scale bar = 200 μm (J, K): 80 μm (L).