Callistochiton elenensis (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

Callistochiton elenensis (G. B. Sowerby I, 1832)

Figures 2G , 6J–K , 7A–K , 8A–B

Distribution. Throughout the Gulf of California, México (including Sinaloa, Sonora, Baja California and Baja California Sur) along Central America Punta Ancón, Santa Elena, Ecuador ( Reyes-Gómez 2016; Kaas & Van Belle 1994).

Type specimens. Kaas & Van Belle (1994) designated the lectotype from BMNH, H. Cuming collection, number 1829/1 .

Type Locality. Puerto Santa Elena, Panamá .

Material examined. 40 specimens, maximum size of 14.8 mm long, 9.2 mm wide. L (n=4); D (n=5); M (n=5); N (n=5); A (n=7); K (n=6); F (n=8).

Habitat. This species was observed to occur in two habitats: intertidal with high wave energy areas attached on medium rocks commonly covered with green and brown algae, and in shallow subtidal (3–8 m depth) on small rocks where it seems to be most abundant. This species was collected with Callistoplax retusa , Chaetopleura hanselmani and Stenoplax limaciformis in subtidal depths. The juveniles of C. elenensis were collected buried in sand on smaller rocks at 6–12 m depth.

Remarks. Callistochiton elenensis exhibits a wide range from the Gulf of California to Ecuador ( Kaas & Van Belle 1994). In México, it has been recorded as common in Baja California Sur ( García-Ríos & Álvarez-Ruiz 2007) and within the southern Gulf of California in Sinaloa ( Ortiz-Arellano & Flores-Campaña 2008). This species is common in Acapulco and northern Guerrero, and according to Reyes-Gómez (2016) it is also common in Jalisco.

Comparing our specimens with the lectotype ( Santa Elena, Panamá), described and illustrated by Kaas & Van Belle (1994), we identified differences in body size and in the number of the pustule rows of the lateral areas as well as the thickening of its nodules. Specimens from Guerrero showed smaller body size reaching up to 14.8 mm and displayed fewer ribs than the lectotype, with 8 ribs on the head valve and 7–9 on the tail valve; the nodules or knobs of the ribs also appeared smaller and more rounded. Examination of specimens from La Paz, Baja California Sur were up to around 20 mm in body length and usually displayed 9 ribs in the head valve and the tail valve has large, thick nodules or knobs. The specimens from Mazatlán showed similarities with La Paz chitons, reaching a large body length (17 mm) and in general, the valve ribs thicken as the specimens reach its maximum size ( Fig. 20L–M ).

Kaas & Van Belle (1994: fig. 67) presented drawings of the radular plates of lectotype of C. elenensis , in which they depicted the central tooth as a large rectangular plate, anteriorly wider than at its base and the minor lateral has a similar shape but is smaller. A closer examination to the radular teeth of specimens from different localities along the Mexican Pacific revealed morphological variation. The central tooth of chitons from La Paz (Playa Balandra, 19.2 mm length) showed a rectangular plate and the minor lateral tooth had a small sub-rectangular shape. The specimens from Playa Manzanillo, Guerrero (Acapulco) possess an oval central tooth ( Fig. 7K ) and a smaller bicuspid minor tooth. However, specimens from northern Guerrero (Troncones) have a central tooth that is sub-rectangular in shape and others irregularly sub-rectangular ( Fig. 8A, B ) and the minor lateral has an irregular bicuspid sub-triangular plate. Little is known about the radular features from specimens of other regions along the latitudinal range of this species. The radular central teeth variation observed in Guerrero chitons, may indicate intraspecific variability, which requires further investigation.

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 6. Ischnochiton muscarius, SEM images of a specimen BL 13.1 mm; valves in dorsal view, A, head valve; B, intermediate valve IV and in ventral view, C, detail or articulamentum of valve IV; D, tail valve in dorsal view. E, aesthete system detail of intermediate valve IV; F, girdle scales; G, detail of girdle scales surface; H, radular teeth; I, detail of major lateral teeth. Callistochiton elenensis, disarticulated valves of a specimen BL 11.09 mm, Manzanillo, Acapulco (CNMO 5304); dorsal view of valves, J, head valve; K, intermediate valve IV.

FIGURE 7. Callistochiton elenensis, disarticulated valves of a specimen BL 10.9 mm, Manzanillo, Acapulco (CNMO 5304); A, dorsal view of tail valve. Valves in ventral view, B, head valve; C, intermediate valve IV; D, tail valve. SEM images of a specimen BL 9.97 mm, valves in dorsal view; E, head valve; F, intermediate valve IV; G, tail valve, and H, ventral view of intermediate valve IV; I, detail of girdle scales; I, radular teeth; J, K, detail of central teeth.

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 20. Chiton articulatus, specimen BL 27 mm, El Faro, Mazatlán (CNMO 5661); shows the tegmentum color details A, head valve; B, intermediate valves III-V; C, tail valve. Specimen BL 24.45 mm, Santa Elena, Oaxaca (CNMO 1066); shows color tegmentum details; D, head valve; E, detail of intermediate valves III-V; F, tail valve. Chaetopleura lurida, G, dorsal view of whole specimen BL 21.3 x 13.7 mm, Estacahuite, Oaxaca (CNMO 5813). Chaetopleura lurida, specimen of 27.9 x 15.4 mm, dorsal view of valve I and IV, Isla Partida, Baja California Sur (CNMO 1004), H, head valve and I, valve IV; J, whole specimen BL 25.8 mm, Sayulita, Nayarit; K, Ischnochiton muscarius, whole specimen BL 27.6 mm in dorsal view.Callistochiton elenensis, L, whole specimen BL 19.46 mm, La Paz, Baja California Sur (UAGRO 0060); M, detail of sculpturing of valves II-IV; N, Chiton articulatus, N, whole specimen in dorsal view, BL 37.2 mm, Sayulita, Nayarit (CNMO 40012).