Leptochiton lascrusesi, 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 : 167-170

Leptochiton lascrusesi n. sp.

( Figs 20–22 )

Types. Holotype (ZISP 2207), now disarticulated consisting of SEM stub of valves I, II V, IV, VIII, part of perinotum and radula, mount of part of perinotum and radula and vial with other valves, and 1 paratype (ZISP 2208).

Type locality. Chile, Las Cruses 33°30’S, 71°37’E, intertidal.

Etymology. Named after type locality.

Material examined. The type material, leg. B. Sirenko, 22.11.2008.

Distribution. Only known from type locality.

Diagnosis. Animal very small, elongate oval. Valves with low elevation, carinated, not beaked, tail valve with mucro in its anterior portion. Tegmentum sculptured with flattened oval granules arranged in longitudinal rows in central areas of intermediate valves and in antemucronal area of tail valve. In other areas granules arranged without any order. Each granule with one megalaesthete and two micraesthetes in front of megalaesthete. Dorsal scales broad with 10–12 distinct riblets. Sutural needles similar to marginal needles, but longer. Major lateral teeth of radula with narrow single cusp.

Description. Holotype 4.0 x 2.7 mm. Shell lowly elevated (dorsal elevation ratio in valve V 0.28), carinated, not beaked. Colour of tegmentum white. Head valve semicircular. Intermediate valves rectangular, valve II with convex anterior margin, other valves with anterior and posterior margins nearly straight, side margin rounded, lateral area not raised. Size of tail valve equal to head, mucro situated anteriorly, slope of short antemucronal area convex, slope of posterior area slightly concave.

Tegmentum sculptured with oval flattened granules (40–50 µm). On head valve, lateral areas of intermediate valves and postmucronal area of tail valve granules arranged quincuncially. Central area of intermediate valves and antemucronal area of tail valve with longitudinal chains of flattened granules. 26 rows of granules in central area of valve V. Each granule with one megalaesthete and two micraesthetes in front of each megalaesthete. Megalaesthete (8 µm) double the size of micraesthetes (3–4 µm).

Articulamentum weakly developed, apophyses short and wide, rounded triangular in valve II and rounded trapezoidal in valve III–VIII. Apophyses wider than jugal sinus.

Girdle very narrow, dorsally densely covered with bluntly pointed scales (45 x 50 µm) with 10–12 distinct riblets. Intersegmental area with long needles (190 x 16 µm). Similar but shorter needles (140 x 13 µm) along margin. Margin with two kind of elongate pointed scales (59– 67 x 13–18 µm) either with two or three riblets. Ventrally girdle covered with elongate, smooth, bluntly pointed scales (55 x 18 µm), next to margin with three short riblets in their distal ventral part.

Radula of paratype (BL— 3.2 mm) 1.5 mm long with 120 transverse rows of mature teeth. Central teeth rectangular, major lateral teeth with short unidentate sharply pointed cusp.

Holotype with 7 gills per side arranged from valve VI to anus.

Remarks. The new species differs from Leptochiton linseae in having 10–12 ribs in dorsal scales (16–17 ribs in L. linseae ), carinated valves (rounded in L. linseae ), an unidentate cusp of major lateral tooth of the radula (tridentate in L. linseae ) and more distinct longitudinal rows on the central area of the valves (vague longitudinal rows in L. linseae ). Leptochiton lascrusesi differs from L. kerguelensis in having three aesthete pores per granule (one pore in L. kerguelensis ), 10–12 ribs on dorsal scales (8–9 ribs in L. kerguelensis ), carinated valves (rounded or subcarinated in L. kerguelensis ), an unidentate cusp of the major lateral tooth of the radula (bidentate in L. kerguelensis ), distinct longitudinal ribs of granules on the central area (striated surface of tegmentum in L. kerguelensis ). The new species differs from L. medinae in having three aesthete pores in each granule (five pores in L. medinae ), 10–12 ribs on dorsal scales (6 ribs in L. medinae ), carinated valves (rounded in L. medinae ), an unidentate cusp of the major lateral tooth of the radula (bidentate in L. medinae ).

Figures

FIGURE 20. Leptochiton lascrusesi n. sp. Holotype, (ZISP 2207). Chile, Las Cruses, BL— 4.0 mm. A. Valve I, dorsal view; B. Valve II, dorsal view; C. Valve V, dorsal view; D. Valve VIII, dorsal view; E. Valve IV, ventral view; F. Valve II, detail of tegmentum surface of central area; G. Valve VIII, detail of tegmentum surface of antemucronal area; H. Valve VIII, lateral view.

FIGURE 21. Leptochiton lascrusesi n. sp. Holotype, (ZISP 2207). Chile, Las Cruses, BL— 4.0 mm. A. Dorsal, marginal and ventral scales and needles; B. Sutural needles and dorsal scales; C. Sutural, dorsal, marginal and ventral scales and needles; D. Dorsal and ventral scales and marginal needles and scales.

FIGURE 22. Leptochiton lascrusesi n. sp. Holotype, (ZISP 2207). BL— 4.0 mm (A – G, K, L) and paratype BL— 3.2 mm (H – J), Chile, Las Cruses. A. Sutural needle; B. Dorsal scales; C. Marginal needle; D, E. Marginal scales; F. Ventral scale in middle part; G. Ventral scale near margin, ventral view; H. Central and first lateral teeth; I. Major lateral tooth; J. Head of major lateral tooth; K. Aesthete group in central area; L. Valve V, rostral view. Scale bar 100 µm (A – J) and 1.0 mm (L).