Ischnochiton muscarius ( Reeve, 1847 )

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 : 457-465

Ischnochiton muscarius ( Reeve, 1847)

Figures 2C–F , 5E–K , 6A–I

Distribution. Isla El Venado, Sonora to La Ventosa, Oaxaca, including Isla Socorro, Revillagigedo, México ( Kaas & Van Belle 1990).

Type specimens. Unascertained, according to Kaas & Van Belle (1990) and Ferreira (1983b).

Type Locality. Unknown, maybe Lower California (according to Kaas & Van Belle 1990) .

Material examined. 169 specimens, maximum size of 30.4 mm long, 15.5 mm wide. L (n=15); B (n=17); G (n=10); H (n=9); D (n=8); M (n=16); K (n=11); P (n=10); U (n=9); Q (n=12); S (n=6); E (n=5); F (n=11); J (n=7); N (n=5); A (n=10); I (n=8).

Habitat. This species is usually found in large aggregations on smooth rocks and with crustose algae. It is particularly abundant in shallow subtidal (2–4 m), buried on small to medium rocks. Juvenile specimens (between 8–16 mm of body length) occur in subtidal to 10 m on small rocks buried in sand. It was collected with C. lurida , T. forbesii and S. limaciformis .

Remarks. This species was one of the most abundant species found during this study comprising 26% of the total specimens collected ( Table 2 ). Color varies from olive green, brown, yellow, or gray ( Figs. 2C–F ); frequently the whole tegmentum area of the intermediate valves (IV or V) is dark green or black in color. We also observed dark, fine longitudinal bands in the lateral areas, directed concentrically to the apex; this pattern was also observed in specimens from Nayarit and Mazatlán. However, chitons from southern areas in Oaxaca (e.g., CNMO 5662) lack the characteristic chessboard pattern located on head and tail valve ( Fig. 20K ), as well as the olive-green or dark brown dots on the central areas.

Family Callistoplacidae Pilsbry, 1893

Figures

FIGURE 1. Location of sampling sites within the coastline of Guerrero, from north to south:A) Troncones, B) Isla Grande, C) El Capricho, D) Las Gatas, E) Barra de Potosí, F) La Barrita, G) Puerto Vicente Guerrero, H) Ojo Agua, I) Tlacoyunque, J) Pie de la Cuesta, K) Parque de la Reina, L) Muelle, M) Manzanillo, N) Tlacopanocha, O) Palmitas, P) Majahua, Q) Playa Ventura, R) Casa de Piedra, S) Las Salinas, T) Peñitas, U) Punta Maldonado.

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 5. Chaetopleura hanselmani, SEM images of a specimen BL 10.9 mm; A, girdle spicules; B, detail of spicules ornamentation; C, radular teeth; D, detail of central and minor lateral teeth. Ischnochiton muscarius, disarticulated valves of a specimen BL 22.31 x 11.95 mm, Las Gatas, Zihuatanejo de Azueta, (CNMO 5183). 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. K, detail of girdle scales.

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 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).

Tables

TABLE 2. Geographic localization of the collecting sites and description of the wave and substrate type. The code

Site	Code	Georeferences	Wave exposure	Type of substrate
Costa Grande Region
Troncones, La Unión	A	17°47' 35.2''N, 101°44' 46.6''W	High	Blocks, large rocks
Isla Grande, Teniente José Azueta El Capricho Las Gatas, Zihuatanejo Barra de Potosi, Petatlán La Barrita, Petatlán Puerto Vicente Guerrero Ojo de Agua, Tecpan de Galeana Tlacoyunque, Tecpan de Galeana Acapulco Region	B C D E F G H I	17°40' 36.8''N, 101°39' 16.7''W 17°38' 12.7″N, 101°33' 05.8″W 17°37' 17.5''N, 101°33' 14.2''W 17°37' 17.5''N, 101°33' 14.2''W 17°24' 32.7''N, 101°10' 51.3''W 17°16' 34.2''N, 101°03' 19.2''W 17°18' 34.8''N, 101°03' 04.9''W 16°19' 35.4''N, 98° 34' 12.6''W	Medium Medium Low Low High Medium High High	Blocks, large rocks Large and medium rocks Large and medium rocks Rock masses and large rocks Blocks, large and medium rocks Blocks and large rocks Large and medium rocks Blocks, large rocks
Pie de la Cuesta Parque de la Reina	J K	16°52' 25.6''N, 99°56' 34.6''W 16°50' 58.2''N, 99°54' 01.8''W	High Medium	Rock masses and large rocks Large and mediums rocks

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