Leptochiton hiriensis, Schwabe & Lozouet, 2006

Schwabe, Enrico & Lozouet, Pierre, 2006, Chitons (Mollusca, Polyplacophora) from Rapa, the southernmost island of Polynesia, Zoosystema 28 (3), pp. 617-633 : 619-621

Leptochiton hiriensis n. sp.

( Figs 2-4 ; 10A)

TYPE MATERIAL. — Holotype: type locality ( MNHN).

Paratypes: type locality, 7 paratypes ( MNHN). — Stns 16 and 30, 2 paratypes ( ZSM).

TYPE LOCALITY. — French Polynesia, archipel des Australes, Rapa, Baie de Hiri, RAPA 2002, stn 9, 27°37.3’S, 144°22.2’W, 3-24 m, coral bottom.

ETYMOLOGY. — From the type locality.

MATERIAL EXAMINED. — A total of 25 specimens (3 lots). French Polynesia. Rapa Island, Baie de Hiri, 27°37.3’S, 144°22.2’W, RAPA 2002, stn 9, 3- 24 m, coral bottom, 8 spms. — W of Tauna islet, 27°36.3’S, 144°18.4’W, RAPA 2002, stn 16, 5 m, dead corals, 13 spms. — Pointe Mei, 27°38.2’S, 144°18.2’W, RAPA 2002, stn 30, 16- 20 m,

dead corals, 4 spms.

Schwabe E. & Lozouet P.

DIAGNOSIS. — Elongate-oval animal, minute.Tegmentum strongly sculptured with comarginal ridges. Dorsal girdle with strongly ribbed scales and long needles. Ventral girdle with smooth, elongate-rectangular scales. Radula with c. 80 rows, about 365 µm in length. Central tooth broad rectangular with a simple inwardly directed blade, second lateral with an elongate-rectangular, tridentate head. Ctenidia unknown.

Chitons (Mollusca, Polyplacophora) from Rapa

FIG. 3. — Leptochiton hiriensis n. sp., paratype, Rapa Island , RAPA 2002 , stn 16, 1.3 mm: A, anterior part of the radula ; B, tail valve, left lateral view. Scale bars: A, 10 µm; B, 30 µm.

DESCRIPTION

Minute, to 1.4 mm in length, with an elongateoval outline. Dorsum evenly convex. Head valve comparatively large, posterior margin widely V-shaped with a shallow notch in the centre. Intermediate valves rectangular, without apex, posterior margin concave. Tail valve semicircular with a central, slightly elevated, posteriorly directed mucro. Postmucronal slope flat and straight. Lateral areas of intermediate valves moderately elevated.

Tegmentum sculptured with relatively prominent, comarginal ridges (12 in the head valve of the holotype), which are stronger towards the outer margin and lateral areas. Central part of the valves more or less distinctly sculptured and appears partly smooth, except for concentric granulated growth marks. Ridges bearing inconspicuous granules. Each granule with a central macropore of 3.5 µm in diameter. Micropores seem to be present among the granules, on their bases.

Articulamentum builds thin apophyses, triangular in intermediate valves, rectangular in tail valve. They are widely separated and not connected by a sutural lamina.

Perinotum ( Fig. 2 ) very narrow. Dorsally covered with strongly ribbed (with up to 15 ribs), imbricated, rectangular scales, which are 34.5 × 20 µm in size (in situ). There are also long, smooth needles (78.3 ×

Figures

FIG. 2. — Leptochiton hiriensis n. sp., Rapa Island, RAPA 2002: A-C, holotype, stn 9, 5.5 mm; A, complete specimen in dorsal view, anterior region on the right side; B, detail of valve ii, left side; C, sutural region of valves vi-vii, left side; D-F, paratype,stn 16, 1.3 mm; D, head and second valve in situ, dorsal view; E, valve vii, dorsal view; F, tail valve, dorsal view. Scale bars: A, 400 µm; B, C, 10 µm; D-F, 100 µm.

FIG. 4. — Leptochiton hiriensis n. sp., Rapa Island, RAPA 2002: A, holotype, stn 9, 5.5 mm, dorsal girdle scales, next to the suture; B-F, specimen, stn 30, 1.2 mm; B, ribbed marginal scales; C, dorsal girdle needle; D, F, marginal girdle needle, among ventral girdle scales; E, ventral girdle scales. Scale bars: A, C-F, 10 µm; B, 20 µm.