Stenoplax limaciformis (Sowerby, 1832)

Reyes-Gómez, Adriana, Vargas-Ponce, Ofelia, Galván-Villa, Cristian, Salgado-Barragán, José, Esqueda-González, Ma. Del Carmen & Ríos-Jara, Eduardo, 2023, Inventory of chiton species (Polyplacophora) from the rocky intertidal of the Northern Gulf of California, with an illustrated taxonomic key, Zootaxa 5296 (2), pp. 147-178 : 153-154

Stenoplax limaciformis (Sowerby, 1832)

( Figures 2C , 4J–N )

Chiton limaciformis Sowerby in Broderip & Sowerby, 1832: 25–33. Chresonymy and synonymy in Bullock (1985).

Type material. Syntype BMNH 1980007 /1.

Type locality. According to Kaas & Van Belle (1987) at Inner Lobos , Perú; Central America , Guacomayo (the exact location is unknown; it is even unclear from which country in Central America) .

Material examined. Ninety– five specimens, BL 11.2–28.9 mm.

Habitat. In the intertidal, on medium–sized and small rocks with patches of crusty algae and abundant globular tally of the algae Dictyosphaeria Decaisne, 1842 . The algae patches had a maximum diameter of 20 cm.

Remarks. Stenoplax limaciformis has a sculpture of somewhat elevated ribs, the ribs are usually broken at the periphery of the valves and become less broken and can show a zigzag arrangement towards the apex ( Figs. 4J, L ). Lateral areas of valves raised and central areas with narrow longitudinal ribs ( Fig. 4K ). Girdle with small, bent dorsal scales showing eroded surface with 5–9 longitudinal, broken striae ( Fig. 4M ). Radula with tricuspid major lateral and short thin central tooth ( Fig. 4N ).

Stenoplax limaciformis differs from the other species of Stenoplax in body shape and tegmentum sculpture. The morphological characters of S. limaciformis are: 1) high variation in the color pattern of the tegmentum, 2) maximal known body size 35 mm, 3) moderately elevated tegmentum sculpture of irregular and/or inter–cut slats forming nodules, and 4) elongated girdle scales, curved and with longitudinal fine grooves. However, S. sonorana exhibits a gray or olive–green tegmentum color; its maximum size is up to 65 mm; with coarse, elevated tegmentum and long bent spicules.

Stenoplax limaciformis is more similar to the species of the Caribbean ( Stenoplax purpurascens C.B. Adams, 1845 , S. floridana Pilsbry, 1892 , and S. bahamensis Kaas & Van Belle, 1987 ). These morphological similarities were also noted by Ferreira (1978) and Bullock (1985) and were confirmed in a molecular clock (cox1) study by García-Ríos et al. (2014). Bullock (1985) concluded that S. limaciformis shows a greater affinity to S. purpurascens . He noted that S. floridana , S. purpurascens , and S. bahamensis are morphologically similar but can be differentiated by details in shape and arrangement of the tegmentum sculpture, also observed in the Stenoplax species from the Mexican Caribbean discussed by Reyes–Gómez et al. (2017). Bullock (1985) recognized the Caribbean Stenoplax species including S. limaciformis from the Pacific as a complex of “sister species". The phylogeny of this genus requires more in–depth studies that analyze morphological characteristics and DNA regions of more individuals of the species that constitute this genus.

Due to the absence of S. limaciformis in the samples collected at higher latitudes, the present study considers Bahía San Carlos, Sonora as the northern limit of this species. Bullock (1985) reported that the northern limit of this species is located at Puertecitos and La Libertad, Baja California. However, Kaas & Van Belle (1987) mentioned that the distribution of S. limaciformis extends from the Gulf of California to Lobos Island, Perú.

Figures

FIGURE 2. Chiton species obtained from the Northern Gulf of California. A. Dorsal and lateral views of Ischnochiton guatemalensis CUCBACM 00450. B. Dorsal and lateral views of Ischnochiton tridentatus CUCBACM 00453. C. Dorsal and lateral views of Stenoplax limaciformis CUCBACM 00455. D. Dorsal and lateral views of Stenoplax mariposa CUCBACM 00459. E. Dorsal and lateral views of Stenoplax sonorana CUCBACM 00462. F. Dorsal view of Lepidozona clathrata CUCBACM 00464. G. Dorsal view of Lepidozona serrata CUCBACM 00471. H. Dorsal and lateral views of Lepidozona subtilis CUCBACM 00475. I. Dorsal and lateral views of Callistochiton elenensis CUCBACM 00476.

FIGURE 4. A–I. Scanning electron microscope images of one specimen of Ischnochiton guatemalensis CUCBACM 00450. A. Dorsal view of head valve. B. Dorsal view of intermediate valve IV. C. Dorsal view of tail valve. D. Detail of valve IV central area. E. Detail of valve IV aesthetes of central area. Dorsal view of F. Dorsal girdle scales. G. Detail in dorsal view of girdle scales ornamentation. H. Radular teeth. I. Detail of central and minor lateral teeth. Light microscope images (J–L) and scanning electron microscope images (M–N) of Stenoplax limaciformis CUCBACM 00455. J. Dorsal view of head valve. K. Dorsal view of intermediate valve IV. L. Dorsal view of tail valve. M. Dorsal view of girdle scales. N. Radular teeth detail.