Leptochiton commandorensis Sirenko, 2017

Sirenko, B. I., 2023, Indonesian chitons of the genera Belknapchiton Sirenko, Saito et Schwabe, 2022 and Leptochiton Gray, 1847 (Mollusca: Polyplacophora: Leptochitonidae), Ruthenica, Russian Malacological Journal 33 (2), pp. 79-94 : 85

Leptochiton commandorensis Sirenko, 2017

( Figs 10–15 )

Leptochiton sp.1 . – Sirenko, 2013: 148.

Leptochiton commandorensis Sirenko, 2017: 114 , figs 6–8.

Type material. Holotype ( ZISP 2254 )

Type locality. North-western Pacific, near Com- mander Islands, 54°57.4’– 54°57.8’N, 165°47.8’– 165°52.0’E, 4805– 3724 m, pebbles and mud.

Material examined. Holotype. Indonesia, Banda Sea, R / V Vitjaz, cruise 54, stn. 6778, 5°15’S, 128°25’E, 3200 m, 2 spms, BL 5.0–13.0 mm, 11.04.1973.

Distribution. Only known from the Commander Islands, 4805– 3724 m and the Banda Sea, 3200 m.

Remarks. The study of the two Indonesian specimens and their comparison with the holotype ( BL 17.0 mm) revealed a fairly close similarity in the shape and sculpture of the shell, gills, girdle armature and radula teeth of the holotype with the larger Indonesian specimen and some differences between the smaller Indonesian chiton and the two large ones. The differences of a small specimen relate mainly to the shape of the tegmentum granules, which are less elevated and more flattened in a small chiton than in large ones. As for Belknapchiton giganteus , age-related variability is observed in the gradual elongation of the postmucronal area compared to the antemucronal area. The ratio of the length of the antemucronal area to the length of the postmucronal area in the tail valve in chitons with BL 5.0, 13.0 and 17.0 mm are 1.51, 1.30 and 1.16 respectively. It is important to note here that L. commandorensis , unlike B. giganteus , retains a constant number of aesthetes per tegmenum granule equal to 3 with age. The smallest of the available individuals ( BL 5.0 mm) turned out to be a brooding female, as it yielded three 8-valved juveniles measuring 800 x 630 µm in the pallial groove. This is the second brooding record in a deep-sea chitons after Leptochiton incubatus Sirenko, 2017 [ Sirenko, 2017].

Figures

FIG. 10. Leptochiton commandorensis, Banda Sea, Indonesia, 3200 m, BL–13.0 mm. A. Head valve, dorsal view. B. Valve V, dorsal view. C. Valve VIII, dorsal view. D. Valve IV, ventral view. E. Valve V, tegmentum sculpture in central area. F. Tail valve, lateral view. G. Valve V, frontal view.

FIG. 11. Leptochiton commandorensis Banda Sea, Indonesia, 3200 m, BL–13.0 mm.A. Dorsal and ventral scales and marginal needles. B, E. Radula. C. Dorsal scales. D. Dorsal scales and needles.

FIG. 12. Leptochiton commandorensis, Banda Sea, Indonesia, 3200 m, BL–5.0 mm. A. Head valve, dorsal view. B. Valve II, dorsal view.C. Valve IV, dorsal view.D. Valve VIII, dorsal view.E. Valve V, ventral view.F. Valve IV, tegmentum sculpture in central area. G. Valve IV, frontal view. H. Valve VIII, lateral view.