Ischnochiton guatemalensis Thiele, 1909

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 : 151

Ischnochiton guatemalensis Thiele, 1909

( Figures 2A , 4A–I )

Ischnochiton guatemalensis Thiele, 1909:51–56 . Chresonymy and synonymy in Kaas & Van Belle (1990).

Type material. Lectotype ZMB Moll. 102027 ( Kilias 1995).

Type locality. Champerico , Guatemala or Acajutla, El Salvador ( Kaas & Van Belle 1990).

Material examined. Two specimens, BL 6.8–8.1 mm.

Habitat. Under big, semi–humid rocks. The specimens were found on rocks buried in sand with brown and red crusty algae patches.

Remarks. The examination of Ischnochiton guatemalensis revealed microgranular sculpture ( Figs. 4A–C ) of valves, lateral areas somewhat raised ( Fig. 4B ). Each microgranule with 16–19 microaesthetes ( Figs. 4D–E ). Girdle dorsal scales, somewhat bent with 7–10 longitudinal ribs which converge distally ( Figs. 4F–G ). Radula with bicuspid major lateral and narrow central tooth ( Figs. 4H–I ).

According to Kaas &Van Belle (1990), I. guatemalensis shows a continuous distribution in the intertidal, from the Gulf of California to Guatemala. Nevertheless, it has not been registered since Kaas &Van Belle (1990) reported it in their monograph of worldwide living chitons, nor in recent studies such as the ones performed about the fauna from Mazatlán, Sinaloa (Ortiz–Arellano & Flores –Campaña 2008), the Mexican Tropical Pacific (MTP) (Jalisco, Guerrero and Oaxaca) (Reyes–Gómez et al. 2010; Flores-Garza et al. 2012; Galeana–Rebolledo et al. 2014; ReyesGómez et al. 2022) and the coast of El Salvador (García-Ríos et al. 2007). In the present study, we only obtained two individuals from both sites (Bahía la Choya, Puerto Peñasco), indicating that it may be a rare species (with respect to its abundance and occurrence) in the Northern Gulf of California. The absence of reports of I. guatemalensis in some regions of the Gulf and the MTP is also reflected in the lack of representative material of this species in the malacological collections. The report of this species from the northern Gulf of California represents the rediscovery of I. guatemalensis in this region after Kaas & Van Belle's report (1990).

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.