Leptochiton rissoi ( Nierstrasz, 1905 )

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 : 88-89

Leptochiton rissoi ( Nierstrasz, 1905)

Lepidopleurus rissoi Nierstrasz, 1905: 6 , figs 5, 52–55; Fer-

reira, 1979: 163, figs 30–32.

LLeptochiton (Leptochiton) rissoi . – Kaas, Van Belle, 1985: 110, fig. 48, map 24. Type material. Lectotype ( ZMA.MOLL

138601), designated by Ferreira, 1979.

Type locality. Celebes Sea , N of Manado, Indonesia, 3°27.1’N 125°18.7’E, 2053 m ( Siboga, St. 126) .

Distribution. Indian Ocean (off Sumatra Island), Pacific Ocean, Philippines, Indonesia, New Guinea, Solomon Islands, 875–2120 m, more common deeper than 1000 m.

Remarks. The following morphological features of the lectotype were not mentioned in Nierstrasz [1905] and Kaas and Van Belle [1985]: the head valve is 1.2 times wider than the tail valve; the apophysis of the valve V is 1.3 times wider than the jugal sinus; the tegmentum granules are oval on the central area and round on the lateral areas with one megalaesthete and 6 micraesthetes; The head of the major lateral tooth of the radula is bidentate instead of unidentate as mentioned in Kaas, Van Belle [1985].

A study of the lectotype of this species ( ZMA. MOLL 138601) and other available specimens indicate that the number of aesthetes in an aesthete group ranges from 6 to 20, regardless of body size. This variability together with a longitudinal arrangement of the granules is similar to L. vietnamensis Sirenko, 1998 . The main difference between both species is the ratio of the width of the apophysis to the width of the jugal sinus, which is always greater than 1 in L. rissoi (vs less than 1 in L. vietnamensis ).