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 zebra Lyons, 1988 Figures 6 I-K , 11 A-H Material examined. Five specimens; 7.5-11.5 mm long, 3.2-7 mm wide. Laguna Arrecifal Desterrada (CNMO4945), Cabana CONANP (CNMO4979), Laguna Desterrada (CNMO4993). Description. Small-sized chitons, color mainly beige to creamy, with concentric bands in dark brown or green on head, tail valve and the lateropleural areas of intermediate valves (Figure 6 I-K ). Head valve (Figure 11A) semicircular, wider than long, posterior margin straight, apex slightly present. Tail valve (Figure 11B) smaller than head valve; mucro postmedian. Intermediate valves (Figure 11C) with tegmentum wider than long; apex pointy; jugum smooth and wider anteriorly. Insertion plate curved, short on its sides; apophyses long and anteriorly elevated wing-shaped in intermediate valves (Figure 11D); sub-rectangular in tail valve; slits in intermediate valves and in the tail valve are hardly present; slit formula 5/1/2. Tegmentum covered with sub-spatulate pustules, wider on their posterior end and somewhat inflated on their central area (Figure 11E). Girdle in living specimens wide, mostly cream-white colored with dark brown or olive-green, irregular longitudinal bands; covered with small spicules (Figure 11F, G), flattened, elongated and strongly ribbed (7-8 ribs) spicules, the ribs reach and join the spicule apex (Figure 11G); tufts reduced or less dense, with long hyaline spicules (Figure 11F). Radula (Figure 11H) with a pointed tricuspid major lateral tooth, the cusps are of almost the same size; central teeth sub-rectangular or spatulate anteriorly curved outwards. Figure 11. Acanthochitona zebra Lyons, 1988. Scanning electron images of a specimen from Laguna Desterrada (CNMO4993, 9.7 mm length). A dorsal view of head valve (I), SB = 500 μm B dorsal view of tail valve (VIII), SB = 500 μm C dorsal view of intermediate valve IV, SB = 500 μm D ventral view of intermediate IV, SB = 500 μm E intermediate valve IV pustules detail, SB = 100 μm F girdle spicules and tuft, SB = 100 μm G girdle spicules detail, SB = 20 μm H radular teeth, SB = 100 μm . Habitat. Found from the intertidal to the shallow subtidal around 12 m, on living corals, rocks and turtlegrass, T. testudinum . Remarks. Lyons (1988) described morphological variation in this species (figure 118-120, and 121-127 respectively) from Tamarind Beach reef in Grand Bahamas, Dry Tortugas Florida and Puerto Rico. According to those figures, it seems that the Bahamas specimen (figure 118-120, of 10 mm length) showed a wider tegmentum in IV, and a remarkably elongated head valve. A PNAA specimen (11.2 mm) showed similarities with those specimens from Florida ( Lyons 1988 : figure 125, 11 mm), particularly in its rounded tegmentum, which seems to be typical in specimens of nearly the same length, and which is also similar to the type specimen (USNM859319) (15 mm). This specimen is also characterized by a somewhat rounded outline of the tegmentum (Figure 14A). Closer examination of the pustules of the PNAA specimens revealed them to have a somewhat inflated surface on their center (Figure 11E). Lyons (1988) did not call attention to this character state but the pustules are similar in his figures.