Lepidochitona africana, Sirenko, 2023

Sirenko, Boris, 2023, Chitons of the genus Lepidochitona (Mollusca: Polyplacophora) in the Indian Ocean and ordering of species compositions of some genera of the subfamily Tonicellinae, Zootaxa 5228 (3), pp. 292-316 : 299-308

Lepidochitona africana n. sp.

( Figs 9–18 )

Type material. Holotype (ZIN 2433), now disarticulated consisting of SEM-mounted valves I, II, IV, V, VIII, parts of perinotum and radula, mount of part of perinotum and vial with other valves and nine paratypes (ZIN 2434– 2437), four of them partly disarticulated.

Type locality. Indian Ocean , South Africa, Port Alfred, 33°35′30″S 26°53′15″E, intertidal .

Material examined. 10 spms. Indian Ocean, Port Alfred , 33°35′30″S, 26°53′15″E, intertidal, stones on rocks in tide pool, holotype ( ZIN 2433 ), BL 8.6 mm, 21.01.1996, leg. B. Sirenko & I. Smirnov ; Mpenjati , 30°58′21″S, 30°17′03″E, intertidal–0 m, stones in tide pool, 6 paratypes ( ZIN 2434 ) BL 2.7 –9.0 mm, 08.03.2000, leg. B. Sirenko & I. Smirnov ; Cape Recife, Port Elizabeth, Algoa Bay , 34°0'48.49"S, 25°41'28.72"E, underside of small and medium sized boulders in residual rock tide pool, low tide, 0–1 m, 1 spm, BL 7.2 mm, 20– 24.07.2002, leg. Y. Terryn & B. Anseeuw ; Atlantic Ocean, False Bay, Glencairns , 34˚9’48’’S, 18˚25’47”E, intertidal–0 m, stones in tide pool, paratype ( ZIN 2435 ), BL 14.0 mm, 19.03.1996, leg. B. Sirenko & I. Smirnov; Glencairns, 34˚9’48’’S, 18˚25’47”E, intertidal–0 m, stones in tide pool, paratype ( ZIN 2436 ), BL 11.1 mm, 11.03.2000, leg. B. Sirenko & I. Smirnov ; False Bay, Gordon’s Bay Beach, 34°10′00″S, 18°52′00″E, large bay surrounded by razor-sharp rock platforms, underside of large boulders, 1–1.5 m, paratype ( ZIN 2437 ), BL 9.0 mm, 28– 29.07.2002, leg. Y. Terryn & B. Anseeuw.

Distribution. Indian Ocean, South Africa, from Mpenjati to Glencairns, Atlantic Ocean, False Bay, intertidal– 1.5 m.

Diagnosis. Chiton small, up to 14.0 mm, color of tegmentum very variablе from completely flesh-colored or brown to light brown with white, blue or dark brown spots, sometimes uniformlylight brown; valves carinated, little beaked, slightly elevated (dorsal elevation 0.30–0.33), mucro anterior. Tegmentum smooth to the naked eye, all pores of aesthetes rounded and of about the same size. Slit formula 9/1/8–11. Girdle clothed with small, slightly flattened, sharply pointed spicules with 2–3 weakly noticeable longitudinal riblets in upper half; more than 20 tufts of long curved needles between valves and around end valves, second row of tuft of needles arranged near margin; marginal fringe consist of two kinds of needles: smooth and ribbed; ventral scales sharply pointed with 2–3 small, narrow riblets in upper half. Major lateral teeth of radula with tricuspid dental caps, distal part of major uncinal tooth with several slits. Fourteen gills per side in holotype, arranged between valve III and VII.

Description. Holotype small, BL 8.6 mm, elongate oval. Shell lowly elevated (dorsal elevation 0.32), back carinated, valves with side slopes almost straight, little beaked. Color of tegmentum brown with white spots in apex.

Head valve semicircular, posterior margin widely V-shaped, shallowly notched in the middle. Intermediate valves broadly rectangular, front margin anteriorly elevated in valve II, somewhat concave in valves III–VII, hind margin concave at both sides of the prominent apex, lateral areas weakly raised, side margins rounded. Tail valve smaller than head valve, front margin concave, mucro anterior, ratio of length of postmucronal area to length of antemucronal area 1.15, postmucronal slope concave.

Tegmentum apparently smooth. Aesthete pores arranged in radial rows on head valve, lateral areas and pleural part of central areas of intermediate valves and postmucronal area of tail valve, in jugal areas and antemucronal areas pores arranged longitudinally, several faint concentric growth lines visible.

Articulamentum moderately developed, white. Apophyses thin, prominently rounded in intermediate valves, trapezoid in tail valve, insertion plates short, slit formula 9/1/8, slits narrow, slit rays present on all valves, very fine, eaves narrow, porous.

Girdle narrow, width 0.5 mm near valve V, brown with ivory spots near tufts of spicules, dorsally covered with very small, sharply pointed spicules (28 x 14 µm) with 2–3 weakly noticeable longitudinal riblets in upper half; two rows of long curved needles (up to 300 x 28 µm) collected in tufts arranged along the body. One row arranged near valves, and another row arranged closer to the edge of the girdle. Fourteen tufts with 1–3 spicules are located in sutures, six around the head valve and four around the tail valve. Marginal spicules of two kinds: elongate, straight, longitudinally ribbed in dorsal side, sharply pointed needles (200 x 25 µm) and long, smooth needles gradually tapering to a blunt top (200–300 x 28 µm). Ventral part of girdle with two kinds of scales: one row of rectangular scales (70 x 25 µm) along margin and sharply pointed scales (55 x 13 µm) with 2–3 narrow ribs in upper half.

Radula of holotype 2.1 mm long with 28 rows of mature teeth. Central tooth short, with narrow base first lateral teeth elongate, wing-shaped with rounded blade, major lateral teeth with tridentate cusps, central denticle slightly larger, distal part of large uncinal teeth with slits.

Holotype has 14 long gills per side arranged from valve III to valve VII. Nephridiopores and gonopores situated between first and second and second and third gills counted from posterior.

Remarks. An ontogenetic variability of the number of gills was observed in the type material. Specimens with body lengths of 8.6 and 14.0 mm had 14 and 17 gills, respectively. The joint slit formula of five type specimens is 9/1/8–11. Radulae of these specimens were 2.1–3.0 mm in length with 26–28 rows of mature teeth. The largest paratype with BL 14 mm has longer dorsal spicules (60 x 14 µm) than the holotype.

Lepidochitona africana n. sp. differs from L. turtoni and L. dicksae (Algoa Bay, Indian Ocean, South Africa) by having two rows of tufts with long, bent needles (vs. one row in L. dicksae and single, short spines in L. turtoni ), sharply pointed, ribbed dorsal spicules (vs. obtusely pointed and smooth spicules in both species). Moreover, L. africana n. sp. has shorter valves than L. dicksae (the ratio of the width of the valve V to its length is 2.7 in L. africana n. sp. and 2.1 in L. dicksae ).

L. africana n. sp. and L. kaasi Carmona Zalvide & García García, 2000 from the Atlantic Ocean, near the Iberian Peninsula have similar dorsal spicules, but the new species differs from L. kaasi in having a smooth tegmentum (vs. granulated tegmentum in L. kaasi ).

Figures

FIGURE 9. Lepidochitona africana n. sp., A, C, E, F, dorsal views, B, D, lateral views: A, B. S. Africa, False Bay, Glen Cairns, intertidal, paratype (ZIN 2435) BL 14.0 mm; C, D. S. Africa, Port Alfred, holotype (ZIN 2433), BL 8.6 mm; E. S. Africa, False Bay, Gordon’s Bay Beach, paratype (ZIN 2437), BL 9.0 mm; F. S. Africa, Mpenjati, paratype (ZIN 2434), BL 7.7 mm.

FIGURE 10. Lepidochitona africana n. sp., S. Africa, Port Alfred, holotype (ZIN 2433), BL 8.6 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 V, detail of tegmentum surface of central area; G. Valve V, rostral view; H. Valve VIII, lateral view.

FIGURE 11. Lepidochitona africana n. sp., S. Africa, Port Alfred, holotype (ZIN 2433), BL 8.6 mm: A. Dorsal spicules, two kinds of ventral scales, marginal needles and tuft of needles near margin; B. Dorsal spicules, two kinds of ventral scales, marginal needles and rest of tuft of needles among dorsal spicules; C. Dorsal spicules, two kinds of marginal needles and sutural tuft of needles; D. Ventral scales.

FIGURE 12. Lepidochitona africana n. sp., S. Africa, Port Alfred, holotype (ZIN 2433), BL 8.6 mm: A. Radula; B. Central and first lateral teeth of radula.

FIGURE 13. Lepidochitona africana n. sp., S. Africa, Port Alfred, holotype (ZIN 2433), BL 8.6 mm: A. Needle of tuft; B. Dorsal spicule; C. Marginal smooth needle; D. Marginal ribbed needle; E. Ventral rectangular scale; F. Ventral ribbed scale; G. Central tooth and first lateral teeth of radula; H. Head of major lateral tooth of radula. Scale bar 100 µm.

FIGURE 14. Lepidochitona africana n. sp., S. Africa, False Bay, Glencairns paratype (ZIN 2435), BL 14.0 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 V, detail of tegmentum surface of central area; G. Valve V, rostral view; H. Valve VIII, lateral view.

FIGURE 15. Lepidochitona africana n. sp., S. Africa, False Bay, Glencairns paratype (ZIN 2435), BL 14.0 mm: A, B. Dorsal spicules, marginal needles and ventral spicules; C. Dorsal spicules and marginal needles; D. Dorsal spicules, tufts of needles and marginal needles.

FIGURE 16. Lepidochitona africana n. sp., S. Africa, Mpenjati, paratype (ZIN 2434), BL 9.0 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 V, detail of tegmentum surface of central area; G. Valve V, rostral view; H. Valve VIII, lateral view.

FIGURE 17. Lepidochitona africana n. sp., S. Africa, Mpenjati, paratype (ZIN 2434), BL 9.0 mm: A. Dorsal spicules, two kinds of marginal needles and two kinds of ventral scales; B. Dorsal spicules, two kinds of marginal needles, two kinds of ventral scales and sutural tufts of needles; C. Dorsal spicules; D. Dorsal spicules, sutural and near margin tufts of needles and two kinds of marginal needles.

FIGURE 18. Lepidochitona africana n. sp., S. Africa, Mpenjati, paratype (ZIN 2434), BL 9.0 mm: A. Radula; B. Central and first lateral teeth of radula.