Leptochiton linseae, Sirenko, Boris, 2015

Sirenko, Boris, 2015, Shallow and deep-sea chitons of the genus Leptochiton Gray, 1847 (Mollusca: Polyplacophora: Lepidopleurida) from Peruvian and Chilean waters, Zootaxa 4033 (2), pp. 151-202 : 181-182

Leptochiton linseae n. sp.

( Figs 27–29 )

Types. Holotype (ZISP 2224), now disarticulated consisting of SEM stub of valves I, V, VIII, part of perinotum and radula, mount of part of perinotum and radula and vial with other valves, and one paratype (ZISP 2225).

Type locality. Beagle Channel, RV Victor Hensen, st 1045, 54°51.8’S, 69°55.6’W, 210 m (04.11.1994)

Etymology. Named after Dr. Katrin Linse (British Antarctic Survey, Natural Environmental Research Council, Cambridge, UK), who has made a major contribution to the knowledge of Antarctic mollusks.

Material examined. Magellan Strait and Beagle Channel, RV Victor Hensen, st. 888, 53°42.8’S, 70°57.4’W, 104 m, paratype, BL— 3.7 mm, 26.10.1994; st. 1045, 54°51.8’S, 69°55.6’W, 210 m, holotype, BL—4.0 mm, 04.11.1994; RV Hero , st. 402, 53°41’S, 70°24’W, 98-110 m, 4 spms, BL—3.5-4.0 mm, 13.05.1979.

Distribution. Magellan Strait and Beagle Channel, 104– 210 m.

Diagnosis. Animal minute. Valves moderately elevated, rounded, not beaked. Lateral areas not raised. Tail valve with mucro anterior, postmucronal area straight. Central areas with about 28 vague longitudinal rows of weakly raised, rounded granules. Each granule with one megalaesthete and two micraesthetes. Dorsal scales wide, obtusely pointed, with 16–17 distinct ribs. Radula with numerous transverse rows of very small teeth. Central teeth narrow, first lateral teeth narrow and long, major lateral teeth with tridentate cusp. Five gills per side.

Description. Holotype 4.0 x 2.0 mm. Shell elongate-oval, moderately elevated (elevation ratio in valve V 0.35). Valves thin, rounded, not beaked. Color of tegmentum white. Head valve semicircular, wider than tail valve. Intermediate valves rectangular, short and wide, anterior and posterior margins nearly straight, not beaked, lateral margins rounded. Tail valve with anterior mucro, antemucronal slope slightly convex, postmucronal slope nearly straight.

Tegmentum sculptured with weakly raised rounded granules arranged in about 28 vague longitudinal rows in central area of intermediate valves and quincuncially in other areas. Each granule have one megalaesthete and two micraesthetes. Aesthete pores very small and roughly equal size (30–40 µm).

Articulamentum weakly developed, apophyses small and widely separated.

Girdle very narrow, covered wide and obtusely pointed dorsal scales (44–68 x 45 –46 µm) with 16–17 distinct ribs. Sutural needles (172 x 15 µm), long and smooth. There are two kind of marginal armature: elongate, sharply pointed scales (66 x 17 µm) with 4 ribs and long needles (123 x 9 µm). Ventral scales in central part sharply pointed, smooth (50 x 18 µm). Near margin, several rows of similar but larger ventral scales (80 x 33 µm) with 4 riblets on their distal ventral aspect.

Radula of holotype 1.8 mm long with 160 transverse rows of mature teeth. Radula teeth very small. Central teeth narrow, first lateral teeth elongated, major lateral teeth with tridentate cusp, central denticle largest.

Five gills per side arranged from valve VII to anus.

Remarks. Leptochiton linseae n. sp. resembles Leptochiton peruvianus but differs in having three aesthete pores in each aesthete group (seven in L. peruvianus ), 16–17 ribs in dorsal scales (10 ribs in L. peruvianus ), a tail valve narrower than the head valve (tail valve wider than head valve in L. peruvianus ) and 5 gills arranged from valve VII to anus (11 gills arranged from valve V to anus in L. peruvianus ). Leptochiton linseae differs from the cooccuring L. kerguelensis in having a tricuspidate dental cup of the major lateral tooth (bidentate in L. kerguelensis ), three aesthete pores (vs. one in L. kerguelensis ), 16–17 ribs in dorsal scales (vs. 8–9 ribs in L. kerguelensis ) and longitudinal rows of granules in central areas (vs. a striated surface in L. kerguelensis ).

Figures

FIGURE 27. Leptochiton linseae n. sp. Holotype, (ZISP 2224). Beagle Channel, RV Victor Hensen, st. 1045, BL— 4.0 mm. A. Valve I, dorsal view; B. Valve V, dorsal view; C. Valve VIII, dorsal view; D. Valve V, detail of tegmentum surface in central area; E. Valve VIII, lateral view.

FIGURE 28. Leptochiton linseae n. sp. Holotype, (ZISP 2224). Beagle Channel, RV Victor Hensen, st. 1045, BL— 4.0 mm. A, B. Dorsal, marginal and ventral scales; C, D. Central portion of radula.

FIGURE 29. Leptochiton linseae n. sp. Holotype, (ZISP 2224). Beagle Channel, RV Victor Hensen, st. 1045, BL— 4.0 mm. (A – I, K – M) and paratype, (ZISP 2225) (J), Beagle Channel, RV Victor Hensen, st. 888, BL— 3.7 mm. A. Sutural needle; B, C. Dorsal scales; D. Marginal scale; E. Marginal needle; F. Ventral scale in middle part; G. Ventral scale near margin, ventral view; H. Central, first lateral and major lateral teeth; I. Heads of major lateral tooth; J, K. Valve V, rostral view; L. Valve VIII, lateral view; M. Aesthete group in central area. Scale bar 100 µm (A – I) and 1.0 mm (J – L).