Lepidochitona turtoni ( Ashby, 1928 )

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 : 293-299

Lepidochitona turtoni ( Ashby, 1928)

( Figs 1–8 )

Trachydermon (Craspedochilus) turtoni Ashby 1928: 80 , pl. 6, figs 5–8; Ashby 1931: 16,

pl. 2, figs 20–23.

Trachydermon turtoni ; Turton 1932: 209; Ashby & Cotton, 1933: 320.

Lepidochitona (L.) turtoni ; Kaas & Van Belle 1985: 108, fig. 50, map 5.

Lepidochitona turtoni ; Sirenko & Hayes 1999: fig. 1I–M, 3B, 4A–D.

Type material: Turton Collection 1453 (fide Ashby & Cotton 1933). Type locality: South Africa, Port Alfred .

Material examined. 96 spms. Indian Ocean , South Africa, Chelsea Point, 34˚2’46.1’’S, 25˚38’4.6”E, 2 m, on abalone shell, 1 spm, BL 5.0 mm, 19.01.1996, leg. B. Sirenko ; Atlantic Ocean , False Bay, Oatlands, 34˚12’29.42’’S, 18˚27’46.48”E, intertidal, stones on sand, 1 spm, BL 9.2 mm, 16.03.1996, leg. B. Sirenko & I. Smirnov; Rocklands Point, 34˚12’59.04’’S, 18˚27’57.31”E, intertidal–0 m, stones on sand, 5 spms, BL 7.0–8.0 mm, 16.03.1996, leg. B. Sirenko & I. Smirnov ; Boulders , 34˚11’49.20’’S, 18˚27’3.60”E, intertidal–0 m, stones on sand, 2 spms, BL 5.5–6.0 mm, 17.03.1996, leg. B. Sirenko & I. Smirnov; Glencairns, 34˚9’48’’S, 18˚25’47”E, intertidal–0 m, stones in tide pool, 9 spms, BL 4.0–8.0 mm, 23– 24.03.1996, leg. B. Sirenko & I. Smirnov ; Glencairns , 34˚9’48’’S, 18˚25’47”E, intertidal–0 m, stones in tide pool, 2 spms, BL 7.0 mm, 11.03.2000, leg. B. Sirenko & I. Smirnov; Oatlands, 34˚12’29.42’’S, 18˚27’46.48”E, 2.0 m, stones on rocks, 1 spm, BL 7.0 mm, 03.02.2007, leg. B. Sirenko ;, Kommetjie , 34˚8’25’’S, 18˚19’45.1”E, intertidal–0 m, stones in tide pool, 5 spms, BL 7.0–9.0 mm, 20.03.1996, leg. B. Sirenko & I. Smirnov; Klein-Stagkop Point, 34˚9’48’’S, 18˚25’47”E, intertidal, stones on rocks, 50 spms, BL 3.0–9.0 mm, 19– 22.03.1996, leg. B. Sirenko & I. Smirnov ; Hout Bay , 34°2′S 18°21′E, intertidal, stones on rocks in tide pools, 20 spms, BL 4.0–9.0 mm, 12.03.2000, leg. B. Sirenko & I. Smirnov.

Distribution. From Port Alfred (south Indian Ocean) to Hout Bay (south Atlantic Ocean), intertidal to 2 m.

Description. Animal small, up to 9.2 x 4.5 mm, tegmentum completely ivory white or with umber spots, valves rounded or bluntly carinated, not beaked, little or rather elevated (dorsal elevation 0.35–0.44), mucro anterior. All areas of tegmentum smooth except several dozens of small, flattened granules in jugum, rounded pores of megalaesthetes are two to three times larger than slit-like pores of micraesthetes. Both granules and pores arranged in a random manner.

Articulamentum white, semi-transparent, apophyses thin, prominently rounded, trapezoid in tail valve, slit formula 9–11/1/7–10, slit rays clearly visible, eaves narrow, porous.

Girdle of ivory color with yellow band and spots, clothed with small, slightly flattened, round-topped spicules (20–22 x 9–11 µm), no tuft of long needles, but аmong dorsal spicules, short, narrow, round-topped spines (26 x 6 µm) are occasionally found. The latter seem to be homologues to long needles collected in tufts in other members of the genus. Along the margin two kinds of girdle elements are much longer: smooth bluntly pointed needles (95 x 16 µm) and pointed needles with longitudinal riblets in dorsal side. Ventral scales with two scale types: rectangular flattened scales (50 x 18 µm) arranged in one row near the margin and sharply pointed scales (30 x 8 µm) with 3–5 small riblets in upper half.

Wide and narrow studied chitons have similar radula 1.6 mm long with 34–35 transverse rows of mature teeth Major lateral teeth of radula with tricuspid dental caps.

Nine to twelve gills arranged between valves III and VII on each side in a specimen with BL 7.0 mm.

Remarks. It should be noted that there are some differences in the sculpture of the tegmentum and the location of the mucro between the individuals I described examined from False Bay ( South Africa) and the described specimen from the Cape of Good Hope ( Kaas & Van Belle 1985). This seems to indicate intraspecific variability of L. turtoni . I studied two specimens with a narrow and wide shape of the body but the same BL (7.0 mm) from the same lot from False Bay ( Figs 1–8 ). The wider specimen has fewer gills (9 instead of 12 gills in the narrow chiton), more slit-like micraesthetes, a shorter antemucronal area and lower valves (dorsal elevation 0.35 in wider specimen and 0.40 in narrower one). Both studied specimens have an anterior mucro. The mucro was also described as anterior of centre by Ashby (1928, 1931), whereas the mucro is submedian according to Kaas & Van Belle (1985). I did not see radiating rows of granules on the head valve, the lateral areas of the intermediate valves, and the postmucronal area of the tail valve as noted by Kaas & Van Belle (1985). The granules on the jugum and aesthetes pores are arranged in a random manner.

L. turtoni is easy to distinguish from many other species of the genus by the absence of sutural tuft needles. Previously, it was generally believed that this species lacks such needles on the perinotum ( Sirenko & Hayes 1999). However, after examination under a Scanning Electron Microscope, small smooth spines were found on the perinotum ( Fig. 6C ), which may correspond to the long tuft needles in other congeners.

Figures

FIGURE 1. Lepidochitona turtoni, S. Africa, False Bay, Glen Cairns, intertidal: A. Narrow specimen, BL 7.0 mm; B. Wide specimen, BL 7.0 mm.

FIGURE 2. Lepidochitona turtoni, S. Africa, False Bay, Glen Cairns, intertidal, wide specimen, BL 7.0 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 3. Lepidochitona turtoni, S. Africa, False Bay, Glen Cairns, intertidal, wide specimen, BL 7.0 mm: A, B. Dorsal spicules, ventral scales and marginal needles; C. Dorsal spicules; D. Dorsal spicules, ventral scales and marginal needle, view from dorsal side.

FIGURE 4. Lepidochitona turtoni, S. Africa, False Bay, Glen Cairns, intertidal, wide specimen, BL 7.0 mm: A. Radula; B. Central and first lateral teeth of radula.

FIGURE 5. Lepidochitona turtoni, S. Africa, False Bay, Glen Cairns, intertidal, narrow specimen, BL 7.0 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 6. Lepidochitona turtoni, S. Africa, False Bay, Glen Cairns, intertidal, narrow specimen, BL 7.0 mm: A, B. Dorsal spicules, ventral scales and marginal needles; C. Dorsal spicules, arrow show short, narrow, rounded top spine; D. Dorsal spicules, ventral scales and marginal needles, view from dorsal side.

FIGURE 7. Lepidochitona turtoni, S. Africa, False Bay, Glen Cairns, intertidal, narrow specimen, BL 7.0 mm: A. Radula; B. Central and first lateral teeth of radula.

FIGURE 8. Lepidochitona turtoni, S. Africa, False Bay, Glen Cairns, intertidal, narrow specimen, BL 7.0 mm: A. Short, narrow, rounded top spine; 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.