Acanthochitona arragonites ( Carpenter, 1857 ), 2016

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 : 472-473

Acanthochitona arragonites ( Carpenter, 1857)

Figures 2O , 13E–K , 14A–H

Distribution. Throughout the Mexican Tropical Pacific, México. From Sonora, México to Salinas, Ecuador ( Watters 1990).

Type specimens. According to Watters (1990), lectotype by designation of Keen (1958:414), BMNH 1857 /64.907.

Type Locality. Mazatlán , Sinaloa, México .

Material examined. 32 specimens, maximum size 9.9 mm long, 5.8 mm wide. G (n=4); P (n=2); R (n=3); S (n=2); U (n=5); F (n=1); E (n=2); N (n=6); J (n=4); I (n=2); A (n=1).

Habitat. Acanthochitona arragonites occurs mostly in surf areas exposed to wave action. It was found on the underside of large rocks in protected cracks and crevices and is common under red, brown, and green algae. Adult and juvenile specimens are usually found together, but juvenile specimens were also collected at 3–6 m depths buried in sand and on the brown macro-alga Padina pavonica . We also collected adult specimens on medium-sized rocks buried in sand in a sample from 12 m depth ( Table 2 ).

Remarks. Previous works on this species focused exclusively in describing and depicting the tegmentum pustule shape and patterns of aesthete openings ( Watters 1990, 1991; Thorpe in Keen 1971) and a few other aspects of its morphology. In this study, we also describe and illustrate the radular teeth, which are characterized by small central and minor lateral teeth. The girdle spicules bear longitudinal ribs.

According to Watters (1990) this species is known to be rare and almost absent in scientific collections. We believe that this lack of available specimens is due to the difficulty in accessing their habitat, which can be accessed only during the lowest tides.

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 13. Tonicia forbesii, SEM images of a specimen BL 15.2 mm; A, detail of ocelli system in lateral area of intermediate valve IV;B,radularteeth;C, detail of minorandmajor lateral teeth; D, detail ofintermediate valveIV.Acanthochitona arragonites, disarticulated valves of a specimen BL 8.7 mm, Las Salinas, Copala (CNMO 5267). Valves in dorsal view shows the sculpturing details; E, head valve; F, intermediate valve IV; G, tail valve. Valves in ventral view, H, head valve; I, intermediate valve IV; J, tail valve. SEM images of a specimen BL 9.1 mm; valves in dorsal view, K, head valve in dorsal view.

FIGURE 14. Acanthochitona arragonites, SEM images of a specimen BL 8.80 mm, Las Salinas, Copala (CNMO 5267). Vales in dorsal view, A, intermediate valve IV; B, tail valve; C, ventral view of intermediate valve IV; D, detail of pustules of intermediate valve IV; E, detail of the tuft’s hyaline needles; F, detail of girdle spicules; G, radular teeth; H, detail of central and minor lateral teeth. Lepidochitona salvadorensis, disarticulated valves of a specimen BL 10.74 mm, Barra de Potosi Protegida, Zihuatanejo de Azueta (CNMO 5332). Valves in dorsal view, I, head valve; J, intermediate valve IV; K, tail valve; L, ventral view of head valve.