Craspedochiton cf. laqueatus ( Sowerby, 1842 )

Dell’Angelo, Bruno, Gori, Sandro, Baschieri, Leonardo & Bonfitto, Antonio, 2010, Chitons (Mollusca, Polyplacophora) from the Maldive islands, Zootaxa 2673 (1), pp. 1-38 : 22-23

Craspedochiton cf. laqueatus ( Sowerby, 1842)

( Figures 7H–Q , 8A–J , 9A–G , 12L , 13L–M )

Chiton laqueatus Sowerby 1842: 104 .

Phacellozona laqueata: Leloup 1952: 6 , textfigs 2–3, pl. 3. fig. 1.

Craspedochiton laqueatus ; Pilsbry 1893: 285, pl. 39, figs 42–51, pl. 44, fig. 68; Strack 1993: 22, pl. 5, figs 4–5; Saito 1998: 156, figs 2J, 7; 2004: 89, figs 5 A–C; Anseeuw & Terryn 2004: 20, figs 60–61; Schwabe 2006: 21.

Non Acanthochites (Loboplax) laqueatus ; E.A. Smith 1903: 620.

Non Acanthochites (Loboplax) laqueatus ; Melvill 1909 /10: 119 (? = Craspedochiton moebiusi Thiele, 1909 , fide Iredale 1914: 124).

Type: NHM 1988071/1, lectotype designated by Strack (1993: 23) ( Fig. 12M ); NHM 1988071/2-5, paralectotypes ( Figs 12N–Q ).

Type locality: Philippines, Island of Mindoro , Calapan, in coarse sand among small stones, in 9 fms .

Material examined: NHM 1988071/1-5, lectotype and 4 paralectotypes; M13: 2 valves (1 head and 1 intermediate); M23: 1 head valve; M26: 3 valves (1 head and 2 intermediate); M59: 5 spm (20 x 13.5 mm curled, 18.5 x 11.8 mm slightly curled, 16.7 x 11.5 mm slightly curled, 13.5 x 7.5 mm, Fig. 12L , 9 x 5 mm curled); M65: 3 valves (1 head and 2 intermediate); MLD01A: 1 intermediate valve; MLD02A: 9 valves (4 head and 5 intermediate); LB04: 1 head valve; LB05: 5 intermediate valves.

Description: Medium sized animal with a broad oval outline, with the anterior part of the perinotum moderately extended. Colour dirty white with large dark spots, verging to purplish, which can cover the whole valves too, perinotum of a reddish brown colour.

Head valve semicircular, wider than long, anterior margin concave between five distinct slightly elevated radial ribs that correspond to the slits of the articulamentum, posterior margin widely V-shaped. It is sculptured by long oval, flat granules, separated from each other, which become larger toward the outer margin. Intermediate valves broad and rather short, carinated, posterior margin straight with a slightly protruding apex, lateral areas scarcely elevated but clearly marked by a distinct diagonal ridge, which correspond to the slits in the articulamentum. The wedge-shaped jugal area is hardly raised and smooth except for an irregular pattern of hazy granules, with the side margins of the jugum partly sawed. The sculpture consists of densely arranged long oval to rectangular granules in the lateral areas, while granules are less closely arranged and of different size in the central areas, more or less radially directed. Tail valve oval, with a subcentral or slightly anterior mucro, anterior slope straight, posterior slope slightly convex. The antemucronal area is sculptured like the central areas of the intermediate valves, the postmucronal area resembles the lateral areas of the intermediate valves, in both cases the granules are roughly defined and coalescent, and more irregular in shape and size. The aesthetes, inconsistent in number, are arranged in an irregular pattern on the granules. In the small and well separated granules of the head valve can occur 2–3 megalaesthetes and 8–15 micraesthetes.

Articulamentum white and thick. The slits are deep and slightly elevated dorsally, forming a channel. Slit formula: 5/1/5. The teeth are broad and roughed dorsally. Apophyses rounded in the intermediate valves, more rectangular with rounded edges in the tail valve, widely separated by an unconnected sinus.

The anteriorly extended perinotum is dorsally covered with dense, short, smooth, distally curved spines, ca. 35–37.5 x 15–17.5 µ m ( Fig. 8F ), and with dispersed long, slender, curved spicules. There are inconspicuous tufts of a few short, straight, finely striated needles, ca. 440–500 µm in length ( Fig. 8E ). Marginally the perinotum is beset with slender, straight or slightly curved, smooth or finely striated spicules, 460–700 µm in length ( Fig. 8G ). The hyponotum is covered with rectangular scales, strongly ribbed, with the size variable, ca. 90 x 68 µm in the anterior portion, with 18–19 ribs ( Fig. 8H ), ca. 95 x 55 µm in the middle portion, with 16–17 ribs ( Fig. 8I ), ca. 100 x 48 µm in the posterior portion, with 14–16 ribs ( Fig. 8J ). The size of the scales is variable, and these measurements are medium-sized, but the spines become more slender and have fewer ribs on their posterior side. The ribs are very irregular, and it is possible to highlight in many scales a pronounced median rib, giving a characteristic appearance to the scale.

Preparation of the radula for this study was not very successful ( Figs 8A–D ), and the teeth are not well discernible. It is possible to see a large, broad central tooth, with an indication of a slight cusp at the apex ( Fig. 8C ), the first lateral tooth with a thin posterodorsal corner, and the second lateral tooth with a tricuspid blade, with the central denticle being largest ( Fig. 8B ).

Remarks: The Craspedochiton species in Indian Ocean are a very difficult group to understand, based on the scarcity of the material available, the high variability of the species, and the often inadequate original description of the relevant species. The considerations made by Kaas (1979) in his discussion on C. isipingoensis (Sykes, 1901) and by Schwabe (2006) in his discussion of C. tetrica (Carpenter in Pilsbry, 1893), are representative for these problematic aspects.

The only Craspedochiton species reported for the Maldives Islands is C. laqueatus ( Sowerby, 1842) , [E.A. Smith (1903); Melvill (1909 /10)], but Iredale (1914: 124) showed that the specimens of C. laqueatus reported by Melvill from the Amirantes were wrongly identified, and assigned them with some doubts to C. moebiusi Thiele, 1909 . The description of E.A. Smith of the Maldive’s specimen is not sufficient to identify the species with certainty, but he reports the tail valve with “insertion plate thickish, with nine slits”, and this is different from C. laqueatus (5 slits). In addition, E.A. Smith considered C. tetrica as a synonym of C. laqueatus , and these two species are considered to be different now (Schwabe 2006), so it is difficult to say which Craspedochiton species he had in hand when he described the Maldive’s material.

We examined and illustrate for comparison the type material of C. laqueatus ( NHM 1988071 /1-5, Fig. 14A ) :

- the lectotype NHM 1988071/1 ( Fig. 12M ), 17.4 x 11.2 mm, the specimen illustrated by Reeve (1847: pl. 20, Fig. 135);

- the paralectotype NHM 1988071/2, the largest specimen, 17.5 x 11.3 mm, Fig. 12N , with 3 valves detached (head, intermediate ii and tail, Figs 10A–C, 10E–F );

- the paralectotypes no. 1988071/3-5, respectively 11.3 x 6,7 mm, 13.2 x 8.6 mm, and 16 x 10.5 mm ( Figs 12O–Q ).

Our material has valve’s characteristics that agree with those of C. laqueatus , and not of C. tetrica (compare Fig. 7N to Fig. 10E ) while there are some differences in the girdle structures, especially in the ventral formations, as described by Strack (1993) and Saito (1998). It was not possible to study by SEM the girdle formations of the type material of C. laqueatus , the only available image of the hyponotum scales, obtained without cleaning and coating the type material ( Fig. 10D ), shows a rectangular scale, strongly ribbed, 70 x 38 µm, with 17–18 ribs, smaller but similar in shape and sculpture to those of our Maldive’s material. For all these reasons, we identify our specimens as C. cf. laqueatus , waiting for more material and a better knowledge of the Craspedochiton species of the Indian Ocean.

The great variability of the hyponotum formations had rather limited previous documentation, i.e. by Leloup (1952), Strack (1993) and Saito (1998) for C. laqueatus , and by Schwabe (2006) for C. tetrica . But Leloup (1952: 7) also confirmed the great variability of these structures: “ Les deux specimens de Tuticorin montrent quelques différences: ... La ceinture montre , à la face inférieure, chez le premier des écailles de différentes grandeurs dont certaines très grandes; le second a les écailles moyennes et assez semblables de dimensions ”. A revision of Indo-West Pacific Craspedochiton species is absolutely necessary.

The characteristics of the available head and intermediate valves agree with those of C. laqueatus , also if a certain degree of variability is visible, for example the elevation of radial ribs in the head valves and the shape and layout of the granules.

Distribution: Craspedochiton laqueatus is seemingly a widespread Indo-Pacific species known from the northern Red Sea to the Philippines, but exact occurence needs a revision.

Figures

FIGURE 5A–B, Lucilina perligera Thiele, 1909, Maldive, M13, intermediate valve. A, dorsal view. B, tegmentum granules of the central area. C–L, Lucilina carnosa (Kaas, 1979), Maldive. C–D, head valve, MLD02A. C, dorsal view. D, detail of the sculpture. E–F, intermediate valve, MLD02A. E, dorsal view. F, detail of the sculpture. G–I, intermediate valve, M23. G, dorsal view. H, frontal view. I, detail of the sculpture. J–L, tail valve, MLD02A. J. dorsal view. K, lateral view. L, detail of the sculpture of the antemucronal area. Scale bars 1 mm: A, C, E, G, H, J, K; 500 µm: I; 100 µm: B, D, F, L.

FIGURE 7A–D, Acanthochitona penicillata (Deshayes, 1863), Maldive. A–C, intermediate valve, MLD02A. A, dorsal view. B–C, granules, dorsal and lateral views, respectively. D, dorsal view of tail valve, LB05,. E–G, Acanthochitona sp., LB05, intermediate valve. E, dorsal view. F–G, granules, dorsal and lateral views. H–Q, Craspedochiton cf. laqueatus (Sowerby, 1842), Maldive, valves dismounted from living specimen, M59. H–J, head valve. H, dorsal view. I, detail of the sculpture. J, frontal view. K–M, intermediate valve. K, dorsal view. L, frontal view. M, detail of the sculpture. N–Q, tail valve. N, dorsal view. O, ventral view. P, lateral view. Q, posterior view. Scale bars 1 mm: H, J–L, N–P; 500 µm: A, D, Q; 100 µm: E, I, M; 50 µm: B, C, F, G.

FIGURE 8A–J. Craspedochiton cf. laqueatus (Sowerby, 1842), Maldive, living specimen, M59. A–D, radula. A, general view of the radula. B, blades of the second lateral tooth. C, close-up of the central region. D, detail of the first lateral teeth. E–J, girdle elements, in situ. E, dorsal tuft of needles. F, dorsal spines. G, marginal spicules. H, ventral scales in the anterior portion. I, ventral scales in the middle portion. J, ventral scales in the posterior portion. Scale bars 100 µm: A, E, G; 50 µm: B–D, H–J; 10 µm: F.

FIGURE 9A–G. Craspedochiton cf. laqueatus (Sowerby, 1842), valves, Maldive, MLD02A. A–C, head valve. A, dorsal view. B, detail of the sculpture. C, posterior view. D–G, intermediate valve. D–E, dorsal and frontal views, respectively. F–G, detail of the sculpture of the pleural areas. H–K, Craspedochiton sp., tail valve, Maldive, M65. H, dorsal view. I, detail of the right side. J, detail of the insertion lamina teeth. K, lateral view. Scale bars 1 mm: A, D, E, H, K; 500 µm: C, I, J; 100 µm: B, F, G.

FIGURE 10A–F, Craspedochiton laqueatus (Sowerby, 1842), NHM type material, Philippines, Mindoro, Calapan, not coated. A–C, E–F, valves detached from the paralectotype NHM 1988071/2. A–B, head valve, dorsal and lateral views, respectively. C, intermediate valve (ii), dorsal view. E–F, tail valve, dorsal and lateral views. D, hyponotum scale in situ, from the paralectotype NHM 1988071/3-5, length 11.3 mm (Fig. 12Q). Scale bars 1 mm: A–C, E–F; 10 µm: D.

FIGURE 12A, Parachiton hylkiae mauricejayi Schwabe, 2002, living specimen, Maldive, LB03B, length 12.8 mm. B, Ischnochiton albinus Thiele, 1911, living specimen, Maldive, M13, length 5.2 mm. C, Ischnochiton feliduensis E.A. Smith, 1903, Maldive, Felidhoo Atoll, Holotype, NHM 1903.9.17.25, length 6 mm. D, Tegulaplax hululensis (E.A. Smith, 1903), living specimen, Maldive, M28, length 10.5 mm. E–F, Callochiton sp., S. Nilandu Atoll, Maldive, NHM 1903.4.11.71 (living specimen collected by J.S. Gardiner), length 6.6 mm. G, Lucilina sp., living specimen, Maldive, M07, length 4 mm. H, Lucilina indica (Leloup, 1981), holotype (MNHN), Madagascar, Tuléar, length 8 mm. I, Acanthopleura miles (Carpenter in Pilsbry, 1893), living specimen, Japan, Okinawa, Sesoko Island, length 29.2 mm. J, Schizochiton incisus (Sowerby, 1841), living specimen, Indonesia: inside lagoon of Woka Island, off South Halmahera, 1°2.02’S, 128°13.97’E (ZSM Mol 20052075), length 40 mm. K, Acanthochitona penicillata (Deshayes, 1863), living specimen, Maldive, MLD04A, length 6.5 mm. L, Craspedochiton cf. laqueatus (Sowerby, 1842), living specimen, Maldive, M59, length 13.5 mm. M–Q, Craspedochiton laqueatus (Sowerby, 1842), NHM type material, Philippines, Mindoro, Calapan. M, lectotype (NHM 1988071/1), length 17.4 mm. N, paralectotype (NHM 1988071/2), length 17.5 mm. O–Q, paralectotypes (NHM 1988071/3-5), length respectively 16, 13.2 and 11.3 mm. R–S, Cryptoplax burrowi (E.A. Smith, 1884), living specimen, Maldive, M07, length ca. 11.7 mm. T, Cryptoplax burrowi (E.A. Smith, 1884), living specimen, Indonesia, ZSM Mol 20033081, length 25.4 mm. U–X, Cryptoplax burrowi (E.A. Smith, 1884), NHM 1992 053, syntypes, H. Cuming colln., Port Adelaide, S. Australia, length respectively 56.4, 38.5, 47 and 45.1 mm.

FIGURE 13A–B, Callochiton sp., S. Nilandu Atoll, Maldive, NHM 1903.4.11.71 (living specimen collected by J.S. Gardiner), close-up of the head and tail valves. C–H, Lucilina carnosa (Kaas, 1979), valves, Maldive. C–D, head valves, M13, showing differences in the number of ocelli rows, widths 3 and 3.1 mm, respectively. E, intermediate valve, M13, width 3.5 mm. F, tail valve, M13, width 3.3 mm. G–H, anomalous tail valve, dorsal and posterior views, respectively, M20, width 3.2 mm. I–K, Lucilina sp., valves, Maldive. I, head valve, M13, width 3.1 mm. J, intermediate valve, M20, width 4.7 mm. K, tail valve, M65, width 3.4 mm. L–M, Craspedochiton cf. laqueatus (Sowerby, 1842), head and intermediate valves, Maldive, M65, widths 5.7 and 5.2 mm, respectively. N, Craspedochiton sp., tail valve, Maldive, M65, width 5.8 mm. O–R, Cryptoplax burrowi E.A. Smith, 1884, NHM 1881.11.1.100, syntype, detached valves, coll. Coppinger, Port Molle, Queensland. O–P, intermediate valve, length 4 mm, dorsal and right lateral views, respectively. Q, intermediate valve, length 4.2 mm. R, head valve, length 3.5 mm.

FIGURE 14A–C, NHM labels, with informations on type material. A, Chiton laqueatus Sowerby, 1842, 5 specimens (lectotype and 4 paralectotypes), NHM 1988071/1-5. B–C, Cryptoplax burrowi E.A. Smith 1884. B, NHM 1992 053, syntypes, 4 specimens, H. Cuming colln., Port Adelaide, S. Australia. C, NHM 1881.11.1.100, syntype, detached valves, coll. Coppinger, Port Molle, Queensland. D, NHM label of Callochiton platessa Gould, 1846, S. Nilandu Atoll, Maldive, NHM 1903.4.11.71, living specimen collected by J.S. Gardiner (considered as Callochiton sp. in this work).