Chitons (Mollusca, Polyplacophora) from Alacranes Reef, Yucatan, Mexico Author Reyes-Gomez, Adriana Author Ortigosa, Deneb Author Simoes, Nuno text ZooKeys 2017 665 1 36 http://dx.doi.org/10.3897/zookeys.665.10476 journal article http://dx.doi.org/10.3897/zookeys.665.10476 1313-2970-665-1 9117BAF17E9B4E2599EC7C8C6A8F456E Acanthochitona hemphilli (Pilsbry, 1893) Figures 6F, 9 A-K Material examined. Seven specimens; 7-38 mm long, 3.2-21 mm wide. Agregacion Meros (CNMO4939, CNMO4999), Cabezas entre Blanca y Pajaros (CNMO4940), Yate Acatl (CNMO4946), Precio Caribbean (CNMO4941), Laguna Arrecifal (CNMO4997). Description. Large chitons, body of oval shape. Tegmentum mostly red and orange (Figure 6F). Head valve (Figure 9A) semi-rounded, posterior margin "V" shaped, with concave apex, not notched; the pustule formations fade towards apex. Tail valve tegmentum drop shaped (Figure 9B); the pustules arranged concentrically; the postmedian somewhat elevated mucro not pointed (Figure 9B, C). Articulamentum solid, wide, well extending in all valves; wing-like shaped in the intermediate valves and the tail valve, with the slits short like a little opening and located posterior in the tail valve (Figure 9D); slit formula 5/1/2-1. Intermediate valves (Figure 9E) with rounded sides; jugal area narrow, with a pointed apex. Sculpture of semi-reniform pustules, more oval than elongated, with one single aesthete located in the center of the pustule (Figure 9F, G). Girdle wide and covered with small, hyaline smooth spicules (Figure 9H). Ventral spicules long and somewhat curved (Figure 9J). Dorsal tufts with long hyaline spicules (Figure 9I). Radula (Figure 9K) with a tridentate mayor lateral tooth, cusps rounded, the central cusp a little longer than the outer ones; the central tooth of rectangular shape, spatulate, longer than the minor lateral tooth. Figure 9. Acanthochitona hemphilli (Pilsbry, 1893). Scanning electron images of a specimen from Agregacion Meros (CNMO4939, 36.5 mm length). A dorsal view of head valve (I), SB = 1 mm B dorsal view of tail valve (VIII), SB = 1 mm C dorsal view of tail valve (VIII), of specimen from Laguna Arrecifal (CNMO4997, 38 mm length), SB = 1 mm D detail of articulamentum of tail valve (CNMO4997), SB = 1 mm E dorsal view of intermediate valve IV (CNMO4939), SB = 1 mm F pustules detail of tail valve (VIII), SB = 100 μm G detail of pustules of intermediate valve IV, SB = 50 μm H detail of girdle spicules, SB = 100 μm I detail of girdle tuft, SB = 1 mm J detail of ventral spicules of girdle, SB = 0.50 mm K radular teeth, showing central and major lateral teeth, SB = 200 μm . Habitat. Found from the intertidal to the shallow subtidal down to 12 m on rocks associated with crustose coralline red algae. Remarks. The PNAA specimens have more rounded or kidney-shaped pustules that are distributed across all valves (Figure 9F). The slits are shallow or not deep in the intermediate valves. In the tail valve, one of them is regularly absent (Figure 9D). The lack of the second slit on the tail valve was observed in three specimens, although there was no indication of any damage to the girdle or the valves, which sometimes may cause deformities in the articulamentum development. The central tooth of the PNAA species is a long sub rectangular plate, which in contrast to specimens from Puerto Rico ( Garcia-Rios 2003 : figure 133), show a conspicuously elongate-rounded tooth.