Leptochiton guadelupei Sirenko, 2018

Sirenko, Boris I., 2018, A new small chiton (Mollusca: Polyplacophora) from Guadelupe, The Bulletin of the Russian Far East Malacological Society 22 (1 / 2), pp. 55-62 : 56-59

Leptochiton guadelupei Sirenko sp. nov.

Figs. 1–4

urn:lsid:zoobank.org:act:E80A5641-180B-4D5B-A48B-6B11147AEF8A

Ty p e m a t e r i a l. Holotype ( MNHN IM-2013-67001 ) now disarticulated consisting of SEM stub of valves I, II, V, VIII, part of perinotum and radula, mount of part of perinotum and radula and vial with other valves.

Ty p e l o c a l i t y. Western Atlantic , off Guadelupe: Est Petite Terre, Campagne KARUBENTHOS 2012, stn. GD61, 16°11.97′ N, 61°03.96′ W, depth 80 m, BC5071, 26.05.2012.

E t y m o l o g y. Named after Guadelupe.

D i s t r i b u t i o n. Known only from the type locality.

D i a g n o s i s. Animal very small. Valves moderately elevated, carinated, not beaked. Lateral areas raised. Tail valve with mucro anterior. Pleural parts of central areas with well raised oval granules arranged in concentric as well in longitudinal rows. Head valve, lateral areas of intermediate valves and postmucronal area of tail valve with similar granules arranged quincuncially. Each granule with one megalaesthete and four micraesthetes. Dorsal scales wide, obtusely pointed, with 16–17 distinct, double ribs, interstices very narrow. Radula with numerous transverse rows of very small teeth. Major lateral teeth of radula with unidentate cusp, which has deep longitudinal groove on each side.

D e s c r i p t i o n. Holotype very small, BL about 2.0 mm, elongate-oval, moderately elevated (elevation ratio in valve V 0.45). Valves rather thick for the genus, carinated, not beaked. Color of tegmentum white.

Head valve semicircular, wider than tail valve. Intermediate valves broadly rectangular, short and wide, anterior and posterior margins nearly straight, not beaked, lateral margins rounded. Lateral areas raised. Tail valve high, transversely elliptical with anterior mucro, antemucronal area convex, postmucronal area deeply concave.

Tegmentum sculptured with well raised oval granules arranged in more or less quincuncial pattern on head valve, the lateral areas of intermediate valves and on the postmucronal area of tail valve, in longitudinal as well in concentric rows on pleural parts of central areas of intermediate valves and on antemucronal area of tail valve. Jugal areas with flattened granules arranged in a random manner. Each granule has one megalaesthete and four micraesthetes.

Articulamentum well developed, apophyses small and widely separated.

Girdle very narrow, covered with wide and obtusely pointed dorsal scales (50x50 μm) with 16–17 distinct double ribs. Sutures between valves armed with few long and ribbed spicules (210x22 μm). Marginal spicules elongate (110x18 μm) with 6–7 distinct ribs arranged around the spicule. Ventral scales in central part pointed, smooth (42x18 μm) those near margin have 4–5 short, weak ribs on the distal half in ventral side.

Radula of the holotype 0.7 mm long with about 40 transverse rows of mature teeth. Central teeth bulbose near the point base, distal half narrow, first lateral teeth with a narrow cusp and an outward projecting wing, major lateral teeth with unidentate cusp, which has deep longitudinal groove on each side.

The gills were not counted as the specimen was dry and curled up.

R e m a r k s. New species differs from other species of genus Leptochiton known from the western Atlantic ( L. alveolus , L. medinae , L. pergranatus , L. binghami , L. darioi , L. micropustulosus and L. compostellanum ) by having unique sculpture of tegmentum in the form of concentric rows of granules and unidentate cusp of major lateral tooth of radula, which has deep longitudinal groove on each side.

L. guadelupei sp. nov. is more similar to the eastern Atlantic species of the genus Leptochiton ( L. leloupi Kaas, 1979 and L. tenuis Kaas, 1979 ). Both are from the Bay of Biscay. The new species differs from the other ones by having 16–17 double ribs on dorsal scales (vs. 12–14 single ribs in L. leloupi ), the anterior mucro (vs. about central in L. leloupi ), pleural parts of the central areas with well raised oval granules arranged in concentric and longitudinal rows (vs central areas with rather widely separated longitudinal chains of irregularly shaped tubercles mostly composed of several granules cemented together in L. leloupi ). The new species differs from L. tenuis by having broader dorsal scales 50 μm long, 50 μm wide, with 16–17 double ribs on the dorsal scales (vs. 60–70 μm long, 35–40 μm wide with 10–12 single ribs in L. tenuis ), the anterior mucro (vs. the mucro behind the center in L. tenuis ), carinated valves (vs. not carinated in L. tenuis ). L. guadelupei is also similar to L. hiriensis Schwabe et Lozouet, 2006 from Rapa Island, southern Pacific by the sculpture of tegmentum, but differs by having the unidentate cusp of the major lateral tooth of radula, which has a deep longitudinal groove on each side (vs. tridentate cusp in L. hiriensis ), 16–17 distinct double ribs (vs. up to 15 simple ribs in L. hiriensis ) and the high tail valve with the anterior mucro (vs. the low tail valve with the central mucro in L. hiriensis ).

Figures

Fig. 1. Leptochition guadelupei, holotype (MNHN IM-2013-67001), BL 2.0 mm; A – head valve, dorsal view; B – valve II, dorsal view; C – valve V, dorsal view; D – tail valve, dorsal view; E – valve V, ventral view; F – surface of tegmentum in central area; G – valve V, rostral view; H – tail valve, lateral view.

Fig. 2. Leptochition guadelupei, holotype (MNHN IM-2013-67001), BL 2.0 mm; A, C – dorsal scales, marginal spicules and ventral scales; B – dorsal scales; D – part of radula.

Fig. 3. Leptochition guadelupei, holotype (MNHN IM-2013-67001), BL 2.0 mm; A – part of radula; B – central and first lateral teeth of radula.

Fig. 4. Leptochition guadelupei, holotype (MNHN IM-2013-67001), BL 2.0 mm; A – sutural needle; B – dorsal scale; C – marginal needle; D – ventral scale near margin; E – ventral scale in middle part; F – central and first lateral teeth of radula; G – heads of major lateral teeth of radula; H – aesthete group on central area. Scale bar 100 µm.