taxonID	type	description	language	source
1B1DC90AE80006583BCBFB851657FAD1.taxon	type_taxon	Type species. Leptochiton belknapi Dall, 1878, by original designation [Sirenko et al., 2022]. Genus distribution. Pacific, Indian and Atlantic oceans. Pacific Ocean, from Asia to America and from Bering Sea to south Australia and New Zealand, Pliocene – Recent, 92 – 4600 m, mainly deeper than 200 m.	en	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): 79-94, DOI: 10.35885/ruthenica.2023.33(2).4, URL: http://dx.doi.org/10.35885/ruthenica.2023.33(2).4
1B1DC90AE800065C3BA9FA3C154AF8C6.taxon	description	(Figs 1 – 9)	en	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): 79-94, DOI: 10.35885/ruthenica.2023.33(2).4, URL: http://dx.doi.org/10.35885/ruthenica.2023.33(2).4
1B1DC90AE800065C3BA9FA3C154AF8C6.taxon	materials_examined	Type material. Lectotype (ZMA. MOLL. 138622), and 2 paralectotypes (ZMA. MOLL. 138611), desig - nated by Ferreira [1979]. Type locality. Indonesia, the Banda Sea, 6 ° 24 ’ S, 124 ° 39 ’ E, 2798 m. Material examined. Lectotype (BL 42 mm) and 2 paralectotypes (BL 25 and 33 mm). Indonesia, Banda Sea, R / V Vitjaz, cruise 54, stn. 6778, 5 ° 15 ’ S, 128 ° 25 ’ E, 3200 m, 4 spms, BL 5.0 – 26.0 mm, 11.04.1973.	en	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): 79-94, DOI: 10.35885/ruthenica.2023.33(2).4, URL: http://dx.doi.org/10.35885/ruthenica.2023.33(2).4
1B1DC90AE800065C3BA9FA3C154AF8C6.taxon	distribution	Distribution. The species is only known from two stations in the Banda Sea, Indonesia, 2798 – 3200 m. Revised diagnosis. Animal elevated, intermediate valves rather wide, carinated, not beaked, tail valve triangular, mucro postmedian, postmucronal slope convex; tegmentum sculptured by small elongate granules arranged in quincunx; each granule with one megalaesthete and 8 micraesthetes; dorsal scales without ribs or rarely with 1 – 3 obsolete longitudinal riblets; central tooth of radula wide, major lateral teeth with sharply pointed, unidentate head, 13 – 14 gills per side. Amended description. Chiton large (BL of the lectotype 42 mm) elongate oval in outline. Valves carinated, moderately elevated (elevation ratio 0.34 – 0.40 in valve V), not beaked. Tegmentum white in color. Head valve semicircular, wider than tail valve, posterior margin widely V-shaped. Second valve oval, anterior and posterior margins convex. Other intermediate valves almost rectangular, lateral areas not raised, anterior margin slightly concave in central part, posterior margin weakly convex, lateral areas not raised. Tail valve triangular, mucro postmedian, antemucronal slope slightly convex, postmucronal slope concave. Tegmentum uniformly sculptured with elongateoval granules in central areas, or rounded ones in head valve and lateral areas of intermediate valves, arranged quincuncially, each granule with one megalaesthete and 8 micraesthetes. Surface of tegmentum in central areas between granules smooth. Articulamentum well developed, apophyses small, widely separated, subtriangular in valves II – VII, more or less trapezoidal in tail valve, jugal sinus wider than apophyses. Girdle narrow (0.7 mm near valve V), dorsally covered with elongate, pointed scales, without ribs or rarely with 1 – 3 obsolete longitudinal riblets (60 x 32 μm), Sutural and marginal needles smooth, not numerous, flattened (140 x 30 μm). Ventral scales lanceolate, smooth (80 x 30 μm). Radula of specimen with BL 21 mm is 6.6 mm long with 32 transverse rows of mature teeth. Central tooth wide with round, narrow blade, major lateral teeth with sharply pointed, unidentate head. Thirteen gills per side extending from valve VII to anus in specimen with BL 21 mm. Nephridiopore situated between twelve and thirteen gills, gonopore situated between thirteen and fourteen from tail gills in lectotype.	en	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): 79-94, DOI: 10.35885/ruthenica.2023.33(2).4, URL: http://dx.doi.org/10.35885/ruthenica.2023.33(2).4
1B1DC90AE800065C3BA9FA3C154AF8C6.taxon	discussion	Remarks. This species is most similar to Belknapchiton bergenhayni (Saito, 2011) which also has 8 micraesthetes per granule, but differs from it by the absence or very absolete riblets in dorsal scales (vs 10 – 12 well developed riblets in B. bergenhayni), and the absence of small longitudinal grooves between the granules (vs small longitudinal grooves between the granules in the central area of the intermediate valves in B. bergenhayni). Six specimens of B. giganteus of different sizes with BL 5.0 – 42.0 mm allowed the study of the age variability of some features of this species (Table 1). With increasing body size, the number of gills naturally increases from 5 in chitons with a body length of 5.0 mm to 16 in the 42.0 mm long lectotype. With the growth of the body, the apophyses gradually expand, while the ratio of the width of the jugal sinus to the width of the apophysis decreases. Also, with an increase in body size, the postmucronal area lengthens more quickly compared to the antemucronal area and the number of micraesthetes on granules increases from 2 – 4 in chitons with BL 5.0 mm up to 8 in chitons with BL 21.0 mm. In addition, the granule size in the central areas increases with size from 50 µm in chitons with a body length of 5.0 mm to 75 µm in individuals with a body length of 21.0 mm and also the distance between neighboring grains increases with size. Small chitons with a body length of 5.0 mm have rounded shell valves, which become carinated with larger sizes.	en	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): 79-94, DOI: 10.35885/ruthenica.2023.33(2).4, URL: http://dx.doi.org/10.35885/ruthenica.2023.33(2).4
1B1DC90AE804065F3BBBF82E161EFA5B.taxon	materials_examined	Type material. Lectotype (ZMA. MOLL. 138623), and paralectotype (ZMA. MOLL. 138612), designated by Ferreira [1979]. Type locality. Indonesia, Strait of Macassar, 0 ° 34.6 ’ N, 119 ° 8.5 ’ E, 1301 m.	en	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): 79-94, DOI: 10.35885/ruthenica.2023.33(2).4, URL: http://dx.doi.org/10.35885/ruthenica.2023.33(2).4
1B1DC90AE804065F3BBBF82E161EFA5B.taxon	distribution	Distribution. Only known from the type locality.	en	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): 79-94, DOI: 10.35885/ruthenica.2023.33(2).4, URL: http://dx.doi.org/10.35885/ruthenica.2023.33(2).4
1B1DC90AE804065F3BBBF82E161EFA5B.taxon	discussion	Remarks. This species differs from other relatives by dorsal scales with six longitudinal ribs and carinated valves. It is necessary to compare this species with B. japonicus (Thiele, 1909), which is widespread not only off the coast of Japan, but also off New Caledonia and the Solomon Islands [Sirenko, 2016].	en	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): 79-94, DOI: 10.35885/ruthenica.2023.33(2).4, URL: http://dx.doi.org/10.35885/ruthenica.2023.33(2).4
1B1DC90AE807065E3BB5F8F81306F84D.taxon	description	(Figs 10 – 15)	en	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): 79-94, DOI: 10.35885/ruthenica.2023.33(2).4, URL: http://dx.doi.org/10.35885/ruthenica.2023.33(2).4
1B1DC90AE807065E3BB5F8F81306F84D.taxon	materials_examined	Type material. Holotype (ZISP 2254) Type locality. North-western Pacific, near Commander 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.	en	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): 79-94, DOI: 10.35885/ruthenica.2023.33(2).4, URL: http://dx.doi.org/10.35885/ruthenica.2023.33(2).4
1B1DC90AE807065E3BB5F8F81306F84D.taxon	distribution	Distribution. Only known from the Commander Islands, 4805 – 3724 m and the Banda Sea, 3200 m.	en	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): 79-94, DOI: 10.35885/ruthenica.2023.33(2).4, URL: http://dx.doi.org/10.35885/ruthenica.2023.33(2).4
1B1DC90AE807065E3BB5F8F81306F84D.taxon	discussion	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].	en	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): 79-94, DOI: 10.35885/ruthenica.2023.33(2).4, URL: http://dx.doi.org/10.35885/ruthenica.2023.33(2).4
1B1DC90AE807065F3BFEF9A81694F8A6.taxon	type_taxon	Type species. Chiton cinereus sensu Montagu, 1803 (non Linnaeus, 1767) = Leptochiton asellus (Gmelin, 1791) fide Lovén (1846), by subsequent designation [Gray 1847]. Genus distribution. Worldwide, Carboniferous – Recent, intertidal to 7657 m.	en	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): 79-94, DOI: 10.35885/ruthenica.2023.33(2).4, URL: http://dx.doi.org/10.35885/ruthenica.2023.33(2).4
1B1DC90AE80806533BDCF8361276F85F.taxon	materials_examined	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).	en	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): 79-94, DOI: 10.35885/ruthenica.2023.33(2).4, URL: http://dx.doi.org/10.35885/ruthenica.2023.33(2).4
1B1DC90AE80806533BDCF8361276F85F.taxon	distribution	Distribution. Indian Ocean (off Sumatra Island), Pacific Ocean, Philippines, Indonesia, New Guinea, Solomon Islands, 875 – 2120 m, more common deeper than 1000 m.	en	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): 79-94, DOI: 10.35885/ruthenica.2023.33(2).4, URL: http://dx.doi.org/10.35885/ruthenica.2023.33(2).4
1B1DC90AE80806533BDCF8361276F85F.taxon	discussion	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).	en	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): 79-94, DOI: 10.35885/ruthenica.2023.33(2).4, URL: http://dx.doi.org/10.35885/ruthenica.2023.33(2).4
1B1DC90AE80D06573BDCFA0116EDFE8A.taxon	materials_examined	Type material. Lectotype (ZMA. MOLL. 138607) designated by Kaas and Van Belle [1985], and 2 paralectotypes (ZMA. MOLL. 138606, ZMA. MOLL. 138625) (see below). Type locality. Indonesia, Strait of Makassar, 0 ° 34.6 ’ N, 119 ° 8.5 ’ E, 1301 m. (Siboga, St. 88) The paralectotypes were found in the Sea Bali, 7 ° 15 ’ S, 115 ° 15 ’. 6 ’ E, 289 m (Siboga, St. 12).	en	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): 79-94, DOI: 10.35885/ruthenica.2023.33(2).4, URL: http://dx.doi.org/10.35885/ruthenica.2023.33(2).4
1B1DC90AE80D06573BDCFA0116EDFE8A.taxon	distribution	Distribution. Only known from the type locality of the lectotype.	en	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): 79-94, DOI: 10.35885/ruthenica.2023.33(2).4, URL: http://dx.doi.org/10.35885/ruthenica.2023.33(2).4
1B1DC90AE80D06573BDCFA0116EDFE8A.taxon	discussion	Remarks. Sirenko [2020] already discussed the composition of the type specimens of this species. A thorough study of the lectotype and two paralectotypes revealed their morphological heterogeneity. The two paralectotypes differ from the lectotype in the arrangement of granules on the central areas in quincuncialy and in the absence of chitinous silky hairs between the valves, the main feature of this species, which served as the basis for the description of the subgenus Pilsbryella Nierstrasz, 1905. They most likely belong to the genus Nierstraszella Sirenko, 1992 for a number of morphological features: 1) arrangement of false tegmentum granules in a quincunx pattern, 2) subcarinated valves, 3) elongated dorsal spicules-scales, 4) a tridentate cusp of the major lateral tooth, which is typical for juvenile individuals of Nierstraszella [Sirenko, 1992] and 5) the paralectotypes were found on a piece of sunken wood which is a very typical substrate for Nierstraszella. By the way, two species of chitons: Leptochiton longisetosus Sigwart et Sirenko, 2012 and L. dykei Sigwart et Sirenko, 2012 [Sigwart, Sirenko, 2012] have long silky intersegmental bristles very similar to the hairs described by Nierstrasz for Lepidopleurus (Pilsbryella) setiger.	en	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): 79-94, DOI: 10.35885/ruthenica.2023.33(2).4, URL: http://dx.doi.org/10.35885/ruthenica.2023.33(2).4
