Cryptoplax dupuisi Ashby, 1931

Dell’Angelo, Bruno, Prelle, Giovanni, Sosso, Maurizio & Bonfitto, Antonio, 2011, Intertidal chitons (Mollusca: Polyplacophora) from southern Madagascar, African Invertebrates 52 (1), pp. 21-21 : 30-34

Cryptoplax dupuisi Ashby, 1931

Figs 3Q–X , 4I–X

Cryptoplax dupuisi: Ashby 1931: 13 , pl. 2, figs 14, 15; Leloup 1940: 19, text-figs 6, 7, pl. 3, fig. 2; FischerPiette & Franc 1960: 1783, fig. 1567; Kaas 1979: 876 (only for specimen 40 mm long from

Conducia Bay); Ferreira 1983: 289; Kaas & Van Belle 1998: 64; Slieker 2000: 50, pl. 13, fig. 30;

Dell’Angelo et al. 2004 b: 60; Dinapoli 2004: 65.

Cryptoplax burrowi (non E.A. Smith 1884): Sykes 1907: 33 (fide Kaas 1979; Ferreira 1983).

Not Cryptoplax dupuisi: Kaas 1979: 876 (the specimens 31 mm long from Conducia Bay and 11 mm long from Umkomaas = C. sykesi Thiele, 1909 ).

Description:

Animal vermiform-cylindrical, maximum estimated length more than 80 mm, the largest (curled) measures 75× 10 mm. Characterised by having first three valves in contact and ollowing valves with spaces in between. In some specimens also fourth valves seem in contact, but this depends on dissimilar stretching of girdle in dried specimens. Distance between valves vi and vii generally widest, and distance between valves v and vi wider than between other valves (iv–v and vii–viii), while distance between valves iii and iv is smallest.All specimens except two are deprived of dorsal girdle covering from anterior margin to posterior margin of valve iv, showing underlying, blackish skin. Colour of girdle buffy brown, valves darkish brown in periphery, more clearin central part.

Tegmentum of head valve semi-elliptical, anterior margin rounded, posteriorly straight ( Fig. 4Q ). Second valve of rhomboidal shape, more rounded in anterior part ( Fig. 4R ). Other intermediate valves (iii–vii, Figs 4S–W ) elliptical in shape, more or less elongated, jugal area narrow and complete on all surface only in valves ii-iv, gradually reduced starting from apex in other valves. Tail valve elliptical, with posterior, backward-directed mucro, postmucronal area steep and almost straight ( Figs 4O, 4P, 4X ). Relative size of the valves is represented in Figs 4Q–X ; for a specimen of a length of about 50 mm, valves v–vi are smallest. Tegmentum in uneroded specimens has elongate granules arranged in radial ribs in head valve, fused together towards sides ( Fig. 4M ). In intermediate valves, granules more rounded, less elongated, irregularly arranged, giving an impression of radial or longitudinal ribs starting from apex, more larger and irregular towards anterior valve margin, arranged following growth marks, jugal area smooth ( Fig. 4N ). Antemucronal area of tail valve sculptured like intermediate valves. Growth marks present on all valves.

Articulamentum white, strongly developed, forming large insertion plates. Intermediate and tail valves with large triangular apophyses, which always form a jugal lamina ( Fig. 4P ), except in valves ii and iii. Slit rays not present.

Perinotum wide, appears velvety without tuft pores, dorsally covered by dense, almost straight, conical spicules, ca 156×46 μm at base, generally deeply embedded in thick cuticle, sculptured longitudinally with 8 or 9 striae ( Fig. 3S ). Dorsal spicules do not wholly cover girdle surface, but only from posterior margin of valve iv, showing underlying, blackish skin in dorsal girdle corresponding to first four valves. Marginal fringe shows smooth, obtusely pointed, straight spicules of ca 200–235×55–60 μm ( Fig. 3T ). Ventrally, short, straight, elongate spicules, smooth or with some faint sign of dorsal ribs, ca 45–60×19–23 μm corresponding to girdle area with first four valves ( Fig. 3U ), tending to be more elongate, ca 45–88×19–23 μm corresponding to girdle area with valves v–viii ( Fig. 3V ). Marginal and ventral spicules wholly cover girdle.

Radula ( Fig. 3W ) with a short, rectangular, central tooth, with projecting horse-shoe but blade like; first lateral tooth wing-shaped and slightly curved, with rounded surface in upper part; second lateral tooth with broadly rectangular head, with three obtusely pointed, large denticles, almost equal-sized, outer one slightly shorter than others ( Fig. 3X ).

Comparison and remarks: This species was described from two specimens received by Ashby from P. Dupuis, collected in Madagascar (dimension of holotype 47× 14 mm), but without precise locality. Leloup (1940) found three specimens in the collection of the Brussels Museum (45× 11 mm, 32× 9 mm and 11× 3.5 mm), belonging to the original lot, and with the locality indicated, “Baie de Manafiafi, N. de Fort Dauphin”. Kaas (1979) reported three other specimens, two from Mozambique (Conducia Bay, 40× 11.5 mm and 31× 7 mm) and one from KwaZulu-Natal (Umkomaas, a juvenile curled specimen of length ca 11 mm).

Leloup (1940) observed that the three specimens studied lack the girdle covering from the anterior margin to the posterior margin of valve iv, showing the underlying, blackish skin. The same can be assumed for the two original specimens described by Ashby, from the original figures ( Ashby 1931, pl. 2, figs 14, 15) and by the girdle colour reported in the description (“buffy brown, the anterior portion as far as valve 4 blackish brown”). The same is reported by Kaas for the larger of the two Mozambique specimens, while the other from Mozambique and the specimen from KwaZulu-Natal have a wholly spiculose girdle.

All the 51 specimens studied from Lavanono have the girdle lacking the dorsal spicules corresponding to the first four valves ( Figs 4I, 4J ), except the only specimen preserved in alchol (ca 35× 8 mm, curled) and two dried specimens, 44×10 ( Fig. 4L ), and 45× 9 mm, respectively. The absence of dorsal girdle spicules corresponding to the first four valves seem therefore the normal condition for this species, as already reported by Leloup (1940: 24): “Il est assez malaise d’expliquer ce dépouillement, certainement artificial, chez «tous» les specimens connus à l’heure actuelle”. The two specimens reported by Kaas from Mozambique and KwaZulu-Natal as wholly spiculose with all the valves connected are probably not this species. All the specimens from Lavanono have the first three valves in contact and the following valves with spaces in between, and this is true for the specimens studied by Ashby and by Leloup. The smaller specimen from Lavanono measures 28.5× 4 mm, comparable with the Kaas’s Mozambique specimen (31× 7 mm), and the valves iv–vii are disconnected ( Fig. 4K ). Also the smaller of the specimens reported by Leloup (11× 3.5 mm), comparable with the specimen from KwaZulu-Natal (ca 11 mm) has the valves iv–viii disconnected ( Leloup 1940: 21). Kaas did not illustrate his material, and we follow Ferreira (1983: 289), and consider the second specimen from Mozambique and the specimen from Natal reported by Kaas (1979) not belong to Cryptoplax dupuisi , but are probably to C. sykesi Thiele, 1909 .

The lack of dorsal girdle spicules for the length of the first four valves is unique to this species, but at present we are not able to explain how or why this is present. Some Cryptoplax species live in a hole in corals, or in deep crevices in coralline rocks; Ang (1967: 431), states for Cryptoplax planus Ang, 1967 “They … are very difficult to collect because they occupy very deep crevices with very narrow openings which are just wide enough for them to get in and out”, and Strack (1998: 37, fig. 17) figured a C. planus crawling from its burrow, only the anterior body emerges (mainly at night). They appear to eat coralline algae around the hole ( Littler et al. 1995; Littler & Littler 1999). Rubbing the anterior part of the chiton dorsal girdle on rocks could cause the loss of the dorsal girdle spicules. However other species have the same habitat and do not show such damage to the girdle (e.g. Cryptoplax larvaeformis , as reported in Littler & Littler 1999). Also, this does not explain why only dorsal girdle spicules are missing, and not the marginal and ventral ones.

In conclusion, we do not have an explanation for the loss of dorsal girdle spicules around the first four valves in Cryptoplax dupuisi . The specimens from Lavanono were found under middle-size stones in small sandy pools among the rocks, at a depth of 20–50 cm, so even the “rubbing around the hole” theory does not apply here. The only other record of a chiton with “smooth” dorsal girdle is Acanthochitona fascicularis (L., 1767) from Italy, seen by Dell’Angelo et al. (2004 a).

The Lavanono specimens agree with descriptions and figures of C. dupuisi in Ashby (1931) and Leloup (1940). Some differences are noticed in the girdle’s formation measurements, compared with those reported by Leloup (drawings in 1/175 scale), generally higher than those measured in the studied material: 270–285 μm vs 156×46 μm for dorsal spicules in the Lavanono specimens, 450–600×34–45 μm vs 200–235×55–60 μm for marginal spicules, and 115–140×22 μm vs 45–88×19–23 μm for ventral ones. We consider that these differences in the girdle’s measurements may be attributed to a low accuracy in Leloup’s drawings. The sculpture of the valves is variable, related to the size of the animals, and tends to be more eroded and poorly defined in larger specimens, as already noted by Leloup (1940, fig. 6). For comparison, we illustrate the first two valves of the smaller specimen of the studied material ( Figs 4M, 4N ).

Two Cryptoplax species are known from Western Indian Ocean ( Ferreira 1983; Dell’ Angelo et al. 2004 b), the present C. dupuisi and C. sykesi Thiele, 1909 (from northern Red Sea to South Africa, Socotra, Madagascar, Réunion, Maldives and Mauritius). A third species, C. burrowi (E.A. Smith, 1884) has been reported from the Maldive Islands (Dell’Angelo et al. 2010 a). Kaas (1979) attributed to C. dupuisi specimens of Cryptoplax from East Africa identified at first by Sykes (1900, 1907) as C. striata (Lamarck, 1819) , a species originally described from Australian waters, but this cannot be confirmed, as already noted by Thiele (1909) and Ferreira (1983), who proposed the name C. sykesi for Sykes’s specimens.

Dinapoli (2004) reported two specimens (12 and 15 mm long) of a Cryptoplax sp. from Socotra Island, comparing them with C. sykesi and C. dupuisi , but it is possible that the two specimens belong to a Choneplax species (E. Schwabe, pers. comm.).

Type material: Holotype: “in Ashby collection” (not in SAMA, fide Robert Hamilton-Bruce, pers. comm., June 15, 2010) . Paratype: SAMC (not in Giles & Gosliner’s Catalog, but present in the Museum’s collection, fide Elizabeth Hoenson, pers. comm., May 28, 2010).

Type locality: Madagascar, without precise locality ( Baie de Manafiafi , N. de Fort Dauphin, fide Kaas 1979: 877) .

Material examined: MADAGASCAR: Lavanono, 51 specimens, 50 dried and badly preserved, from 28.5×4 to 75× 10 mm, one in alcohol (ca 35× 8 mm, strongly curled) ( GP, BD, MZB) .

Distribution: Mozambique and Madagascar.

Figures

Fig.3. (A–P) Callistochiton ashbyi (Barnard, 1963),Lavanono, Madagascar, specimen n.6 (Table 1), MZB: (A, B) head valve, dorsal and lateral views; (C–F) tail valve: (C, D) dorsal and lateral views, (E) detail of the sculpture of antemucronal area, (F) detail of longitudinal, granulose riblets; (G–K) intermediate valve: (G) dorsal view, (H) detail of longitudinal, granulose riblets of pleural area, (I) ventral view, (J) detail of slit, (K) frontal view; (L, M) radula: (L) complete view, (M) detail of central, first lateral and major lateral teeth, with the bilobed blade; (N–P) girdle elements: (N) dorsal scales,(O) ventralscales, (P) a single dorsal scale;(Q–X) Cryptoplax dupuisi Ashby, 1931, Lavanono, Madagascar:(Q–V) girdle elements:(Q) “naked” dorsal girdle, in correspondance of valves i–iv,(R) “normal” dorsal girdle of valves v–viii, (S) dorsal spicules,(T) marginal spicules, (U) ventral spicules on valves i–iv, (V) ventral spicules on valves v–viii; (W, X) radula: (W) complete view, (X) detail of an half row of teeth. Scale bars 1 mm (A–D, G, I, K), 500 μm (Q, R), 100 μm (E, F, H, J, L, N, O, S–X) and 50 μm (M, P).

Fig.4.(A, B) Ischnochiton sirenkoi sp. n., Lavanono,Madagascar:(A) holotype MZB 45693, 12.2 ×6.1 mm; (B) a lot ofspecimens showing colour variations,length,from left to right, respectively 17.7,11.3, 11.2, 12, 10 and 9.5 mm; (C) Ischnochiton sansibarensis Thiele, 1909, holotype ZMB 102069, Zanzibar, ca 4 mm; (D–F) Callistochiton ashbyi (Barnard, 1963): (D) Lavanono, Madagascar, specimen n. 2 (Table 1), 23.3 mm; (E, F) holotype SAMC-A9337, an intermediate valve from Cape Infanta,SouthAfrica,dorsal and ventral views,9×3.3 mm; (G)Callistochiton madagassicus Thiele,1909, holotype MNHN,Madagascar,21×14 mm (from original description),some detached valves at left; (H) Chaetopleura chelazziana Ferreira, 1983, Lavanono, Madagascar, 47×31 mm; (I–X) Cryptoplax dupuisiAshby, 1931, Lavanono, Madagascar:(I–K) specimens with the girdle deprived of dorsal spicules on the first four valves; (I, J) adult specimen, 51×12.5mm; (K) the smallerspecimen,28.5×4 mm;(L) specimen with the girdle completely coveredof dorsal spicules, 44×10 mm; (M, N) detail of sculpture of valves i–ii, in situ; (O, P) tail valve, lateral and ventral views, length 6.8 mm; (Q–X) valves i–viii (same scale), width (plates, without apophyses), from left to right, 4.4 mm (i), 3.9 mm (ii), 1.45 mm (iii), 2.65 mm (iv), 1.45 mm (v), 1.45 mm (vi), 2.4 mm (vii), 2.75 mm (viii).