Callistoplax retusa (G. B. Sowerby I, 1832)

Reyes-Gómez, Adriana, Flores-Garza, Rafael, Galeana-Rebolledo, Lizeth, Hernández-Vera, Gerardo, Galván-Villa, Cristian M., Torreblanca-Ramírez, Carmina, Flores-Rodríguez, Pedro, García-Ibañez, Sergio & Ríos-Jara, Eduardo, 2022, Intertidal chitons (Mollusca: Polyplacophora) from the rocky coastline of Guerrero, México, with the description of a new species, Zootaxa 5155 (4), pp. 451-492 : 465-466

Callistoplax retusa (G. B. Sowerby I, 1832)

Figures 2H , 8C–K , 9A–D

Distribution. Islas Tres Marías, Nayarit, México to Panamá ( Kaas & Van Belle 1994).

Type specimens. According to Kaas & Van Belle (1994) the holotype was not found at BMNH; its whereabouts are thus unknown .

Type Locality. Guacomayo and Porto Portrero, Central America ; Kaas & Van Belle (1994) did not specify in which country of Central America the type locality is located. The same authors reported this species global distribution between Islas Tres Marias and Panamá . However, it is not clear if the type locality is at Panamá .

Material examined. 51 specimens, maximum size 24.1 mm long, 11.9 mm wide. K (n=4); N (n=2); H (n=5); Q (n=8); M (n=2); P (n=2); U (n=1); D (n=3); F (n=4); I (n=4); E (n=4); A (n=6); S (n=1); L (n=4); E (n=1).

Habitat. This species was collected in the intertidal attached to big rocks partly buried in sand, covered with brown and red algae, in shallow subtidal (2–6 m), also in high surf areas buried in sand. We occasionally collected several adult specimens at 12 m depth, which were the largest in body size length (24 mm). These chitons were often eroded and usually bearing epibionts like barnacles and polychaete worms, sponges, and crustose algae. The juvenile specimens were mostly found in shallow subtidal (3–6 m) on smaller rocks and shells. Callistoplax retusa was collected with I. muscarius and S. limaciformis .

Remarks. We observed a change in body shape, that is especially pronounced when specimens of adult size (between 20–24 mm) and smaller animals (less than 10 mm of body length) are compared. The latter have an oval body shape, becoming progressively elongated at a length of 12–17 mm. Callistoplax retusa shows a pronounced change of body shape and height as it reaches its maximum body length. Watters (1991) studied the vermiform body shape of the families Leptochitonidae , Ischnochitonidae and Chitonidae . This author found that all these families maintained a geometric similarity regardless of size and are isometrically related to vermiformity and the portion of the body width or the tegmentum dorsal coverage.

Figures

FIGURE 2. Dorsal view of the whole specimens that represent the analyzed species. A, Chaetopleura lurida, BL 27.48 x 15.70 mm, Majahua, Acapulco (CNMO 5229). B, Chaetopleura hanselmani, BL 11.02 x 7.16 mm, Tlacopanocha, Acapulco (CNMO 5804). Ischnochiton muscarius, C, BL 16.62 x 9.77 mm, Angosta, Acapulco (CNMO 5202); D, BL 15.12 x 9.55 mm, Barra de Potosí Protegida, Petatlán (CNMO 5338); E, BL 18.30 x 10.17 mm, Troncones, La Unión (CNMO 5327); F, BL 14.98 x 9.51 mm, La Barrita, Petatlán (CNMO 5315). G, Callistochiton elenensis, BL 12.32 x 7.76 mm, La Barrita, Petatlán (CNMO 5823). H, Callistoplax retusa, BL 20.41 x 9.68 mm, Parque de la Reina, Acapulco (CNMO 5185). Stenoplax limaciformis, I, BL 17.56 x 7.21 mm, Parque de la Reina, Acapulco (CNMO 5179); J, BL 20.12 x 9.15 mm, Tlacopanocha, Acapulco (CNMO 5208); K, BL 17.65 x 8.29 mm, Las Gatas, Zihuatanejo de Azueta (CNMO 5254); L, BL 19.78 x 9.84 mm, Isla Grande, Zihuatanejo de Azueta (UAGRO 0024). Chiton albolineatus, M, BL 23.84 x 14.63 mm, Piedra de Tlacoyunque, Tecpan de Galeana (CNMO 5337). Tonicia forbesii, BL 33.41 x 17.86 mm, Isla Grande, Zihuatanejo de Azueta (CNMO 5255). Acanthochitona arragonites, O, BL 8.80 x 5.2 mm, Las Salinas, Copala (CNMO 5267). Lepidochitona salvadorensis, P, BL 10.63 x 5.7 mm, Barra de Potosi Protegida, Zihuatanejo de Azueta (CNMO 5332).

FIGURE 8. Callistochiton elenensis, SEM images of a specimen BL 11.6 mm, Manzanillo, Acapulco; A, B radular teeth. Callistoplax retusa, disarticulated valves of a specimen BL 17.74 mm; valves in dorsal view, C, head valve; D, intermediate valve IV; E, tail valve. Valves in ventral view shows the articulamentum details; F, head valve; G, intermediate valve IV; H, tail valve. SEM images of a specimen BL 15.1 mm; valves in dorsal view; I, head valve; J, intermediate valve IV; K, tail valve.

FIGURE 9. Callistoplax retusa, SEM images of a specimen BL 15.1 mm, A, girdle bristles detail; B, detail of the ventral girdle spicules; C, radular teeth; D, detail of central and major lateral teeth. Stenoplax limaciformis, disarticulated valves of a specimen BL 20.45 mm, Tlacopanocha, Acapulco (CNMO 5310). Dorsal view of valves, E, head valve; F, intermediate valve IV; G, tail valve. Ventral view of valves, H, head valve; I, intermediate valve IV; J, tail valve. SEM images of a specimen BL 15.6 mm, valves in dorsal view; K, head valve.