Callochiton sp.

Dell’Angelo, Bruno, Gori, Sandro, Baschieri, Leonardo & Bonfitto, Antonio, 2010, Chitons (Mollusca, Polyplacophora) from the Maldive islands, Zootaxa 2673 (1), pp. 1-38 : 11-13

Callochiton sp.

( Figures 4D–F , 12 E–F , 13A–B , 14D )

Material examined: NHM 1903.4.11.71: 1 spm from S. Nilandu Atoll, Maldive Is., 1–36 fms, coll. J.S. Gardiner (labelled Callochiton platessa Gould, 1846 ).

Description: Animal of 6.6 mm length, curled, valves slightly beaked, girdle of moderate width. Tegmentum uniformly light yellowish–red. Girdle of slightly clearer colour, with rather broad, transverse, blackish bands at the sutures of valves i–ii and vii–viii.

Head valve semicircular, with the posterior margin un-notched in the middle. Intermediate valves rectangular, posterior margin concave on both sides of the slightly beaked apex, lateral areas raised. Tail valve semicircular, mucro not elevated and situated subcentrally or somewhat anteriorly, postmucronal slope straight.

Tegmentum sculptured with elongate microgranules, radially arranged in the head valve, the lateral areas of intermediate valves, and the postmucronal area of the tail valve, longitudinally arranged in the central area of intermediate valves and in the antemucronal area of the tail valve ( Fig. 4F ), the rows anteriorly diverging towards the sides. Central areas and antemucronal area with five distinct, deep and broad longitudinal grooves, which become larger towards the lateral margins. Ocelli easily perceptible, numerous and evenly dispersed over the whole head valve, lateral areas of intermediate valves, and postmucronal area of the tail valve, except for a narrow zone along the posterior margin of the head valve and lateral areas of intermediate valves.

Girdle dorsally densely covered with long, imbricated, inwardly directed, fusiform and smooth spicules, ca. 100 µm in length ( Fig. 4F ), with the upper ends rounded.

Remarks: The description is based on the specimen collected by J.S. Gardiner, and reported in Smith (1903) as Callochiton platessa Gould ; we were not allowed to dismount the specimen for further analysis by SEM, and our description is consequently not complete.

E.A. Smith (1903) listed Callochiton platessa Gould , ranging from E. Australia to Polynesia (table on p. 596). According to Kaas & Van Belle (1998: 146) the species is now regarded as a synonym of Ischnochiton versicolor (Sowerby, 1840) , while Callochiton platessa auct. (non Gould, 1852) is considered to be Callochiton crocinus ( Reeve, 1847) , a species living in Australia and New Zealand ( Kaas & Van Belle 1985). C. crocinus is characterized by its larger size (up to 47 mm length), the valves not beaked, and the absence of pits in pleural areas (even if few small pits may be present on valves vi–viii in var. fossa Ashby, 1922 ). These characters don’t agree with those of our specimen, which also do not seem to fully agree with other named Indian Ocean Callochiton species : Callochiton vanninii Ferreira, 1983 (from Somalia, Madagascar, Red Sea and Bahrain), C. levatus Kaas & Van Belle, 1998 (from Madagascar, Réunion, Mauritius and Chagos Archipelago) and C. christamariae Schwabe, 2003 (from Mauritius) have the pleural areas of the intermediate valves and the antemucronal area of the tail valve lacking any sulci ( Kaas & Van Belle 1985; Schwabe 2003).

Callochiton clausadeae Kaas & Van Belle, 1985 (from Madagascar, Mauritius, Réunion, and the Maldive Islands) has a coarser microgranulation of the tegmentum with roundish granules, and a different layout of the more numerous and longer sulci on the pleural areas of the intermediate valves and the antemucronal area of the tail valve ( Kaas & Van Belle 1985).

Callochiton sulcatus Nierstrasz, 1905 (from Indonesia, only known for the lectotype) has a similar, if not identical, arrangement of sulci (compare to Fig. 3B in Schwabe & Ruthensteiner 2001) in relation to the diagonal ridge, but it differs from the Maldive species by its greater size (10.5 mm), the barely visible ocelli (easily perceptible in our species), the presence of several growth lines in the head valve, the lateral areas of the intermediate valves and the postmucronal area of the tail valve (not present in our species), and the length of dorsal girdle spicules (120–275 µm, instead of about 100 µm in our species). Moreover C. sulcatus is very similar to other two Indonesian species, C. subsulcatus Kaas & Van Belle, 1985 and C. schilfi Schwabe & Ruthensteiner, 2001 . The main characters of these species are reported by Schwabe & Ruthensteiner (2001: Table 1).

On the basis of the preceeding analysis, the attribution of this specimen to some previously known Callochiton species from the Indian Ocean, or to a new species is not possible on a single specimen, and requires both additional material for comparison and the examination of the type material of the others Callochiton species. The specimen collected by J.S. Gardiner at the Maldives remains therefore undetermined, as Callochiton sp. but it is possible, with certainty, to exclude the species Callochiton platessa Gould, 1846 from the chiton fauna of the Maldive Islands.

Distribution: Callochiton sp. is known only from the Maldive Islands.

Figures

FIGURE 3A–J, Ischnochiton sp., Maldive, living specimen, MLD03A. A, complete specimen, lateral view. B, detail of valves vii viii, lateral view. C, close-up of head valve. D, detail of the tegmentum covered by very small apical caps patterned with a semi-spherical layout. E–F, half detached intermediate valve, ventral views. G, ventral (left) and dorsal (right) girdle elements in situ. H, detail of perinotum elements in situ. I, J, dorsal and lateral views (respectively) of the apical caps patterned with a semi-spherical layout. K–M, Ischnochiton feliduensis E.A. Smith, 1903, Maldive, Felidhoo Atoll, Holotype, BMNH 1903.9.17.25, an intermediate valve detached (not coated). K, dorsal view. L, close-up of K. M, granules of the central area. Scale bars 1 mm: A; 500 µm: C, K; 100 µm: B, E, F, L; 50 µm: D, G, I, M; 10 µm: H, J.

FIGURE 4A–C, Callochiton clausadeae Kaas & Van Belle, 1985, tail valve, Maldive, M13. A–B, dorsal and lateral views, respectively. C, detail of the sculpture. D–F, Callochiton sp., S. Nilandu Atoll, Maldive, NHM 1903.4.11.71 (living specimen collected by J.S. Gardiner, not coated). D, detail of the sculpture of an intermediate valve. E, dorsal view of the complete specimen. F, girdle dorsal spicules in situ. G–I, Rhyssoplax maldivensis (E.A. Smith, 1903), Maldive, MLD02A. G, intermediate valve, dorsal view. H–I, tail valve, dorsal and lateral views, respectively. J–O, Tegulaplax hululensis (E.A. Smith, 1903), Maldive, M13. J–L, head valve. J–K, dorsal and lateral views. L, detail of the sculpture. M–O, tail valve. M–N, dorsal and lateral views, respectively. O, detail of the sculpture. Scale bars 1 mm: E, G, J, K, M, N; 500 µm: A, B, D, H, I; 100 µm: C, F, L; 50 µm: O.

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).