Acanthochitona roseojugum Lyons, 1988

Reyes-Gomez, Adriana, Ortigosa, Deneb & Simoes, Nuno, 2017, Chitons (Mollusca, Polyplacophora) from Alacranes Reef, Yucatan, Mexico, ZooKeys 665, pp. 1-36 : 5

Acanthochitona roseojugum Lyons, 1988 Figures 6 G–H, 10 A–G

Material examined.

One juvenile specimen; 3 mm long, 1 mm wide. Isla Perez (CNMO4995).

Description.

Small-sized chiton, of a broad oval shape; tegmentum creamy color, with dark and lighter brown small spots; girdle irregularly banded in olive green and white (Figure 6G, H). Valves arched, somewhat elevated, especially the tail valve. Head valve (Figure 10A) wider than long, posterior margin almost straight; pustules directed radially towards the apex, apex smooth. Tail valve wider than long; mucro elevated and shifted somewhat postmedian (Figure 10B). Intermediate valves (Figure 10C) with a wide, smooth jugum, anteriorly somewhat straight; apex strongly pointed; pustules directed radially towards the apex. Articulamentum wide, especially on the tail valve, apophyses wing-shaped; slit formula 5/1/2. Tegmentum with sub-spatulate elongate pustules, with rounded edges, one single megalaesthete and two micraesthetes located at the pustule base (Figure 10D). Girdle covered with short and longer spicules (Figure 10E) and tufts with hyaline long needles (Figure 10F). The spicules are wider on the base and narrowing anteriorly; its apical area with a fine thin longitudinal striate (Figure 10G).

Habitat.

Found in the shallow subtidal at 12 m on rocks, associated with crustose algae.

Remarks.

The PNAA specimen of A. roseojugum display a single sub central megaesthete and two micraesthetes near the pustule base, which coincide with the description of Lyons (1988). Lyons also remarked this species high similarity in the sculpture pattern with A. andersoni Watters, 1981, and he found it difficult to separate these species. He called the few characters he established to distinguish the species from each other “subjective”. We found Lyons’ separation of these species to rely on only slight differences of pustule and valve morphology and body length. A more focused study is needed to clarify whether these nominal species are actually distinct species.