Callochiton neocaledonicus Kaas
Creators: name: Schwabe, Enrico
name: Sirenko, Boris I.
name: Seeto, Johnson
Publisher: name: Zenodo
Year: 2008
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Polyplacophora
Chitonida
Callochitonidae
Callochiton
Callochiton neocaledonicus

description: Callochiton neocaledonicus Kaas & Van Belle, 1990
(Figures 1 E, 2A–F, 3A–F)
Callochiton neocaledonicus Kaas & Van Belle 1990: 26, fig. 10; 1998: 129; Strack 1996: 168.
Locus typicus: New Caledonia, off Nouméa [22°16’S 166°27’E], 9 m.
Primary type: Holotype (MNHN 6059).
Material examined: ZSM Mol 20061630: 1 adult spm, Viti Levu, Laucala Bay, north side of Nukumbutho Island 18°10.474'S 178°28.343'E; lowest low tide, landward in calm water close to the beach, 0.5 m depth, on the inside of a dead shell, leg. Enrico Schwabe, 21 August 2006, wet; ZSM Mol 20070149: 2 valves, Viti Levu, Laucala Bay, west side of the Nukumbutho channel of the fringing reef opposite the USP, 18°10.899'S 178°27.971'E, pieces of dead corals, found among coral blocs, strong current, low amount of living corals, about 1 m, leg. Enrico Schwabe, 24 August 2006, dry; ZISP: 1 adult spm, Cicia Island [17°45’S 179°18’W], Callisto St. 87, 45 m, leg. Boris I. Sirenko, 0 6 February 1975, wet; ZISP: 1 juvenile spm, Vekai Island [17°34’S 178°49’W], Callisto St. 94, 8 m, leg. Boris I. Sirenko, 0 8 February 1975, wet.
Habitat: The species bathymetrically ranges from 0.5– 45 m. It may found on the underside of hard substratum.
Distribution: The species is known from New Caledonia and Fiji.
Remarks: Species of the genus Callochiton are in most cases difficult to identify. The material under study was identified as Callochiton neocaledonicus Kaas & Van Belle, 1990 via SEM and a direct comparison with the holotype. Besides the holotype, additional specimens from New Caledonia were examined via SEM. A short description of the Fijian material is given here:
Description. Animal small (largest specimen 7.2 mm in length), elongate oval (Fig. 1 E), subcarinated (Fig. 2D), dorsal elevation of valve ii 0.36. General surface appearing smooth but microgranulated. Head valve (Fig. 2A) semicircular with wide V-shaped posterior margin, slightly notched in middle, anterior slope straight, steep (Fig. 2B). Intermediate valves (Figs 1 E, 2C) more or less rectangular with highly elevated lateral areas, protruding apex. Pleural areas with deep, longitudinal sulci (about 3), only outer portion reaching margin of anterior valve. Jugal area without sculpture. Head valve, jugal area, postmucronal area smooth, except for microscopic fine lirae and growth lines. Tail valve (Figs 2E, F) semicircular, mucro central, elevated, forward-directed. Antemucronal area with up to 4 slightly inward-directed sulci, near the jugum not reaching anterior margin. Postmucronal slope steep, straight, slightly concave immediately behind mucro. Black pigmented shell eyes present in head valve, lateral areas, postmuconal area.
Articulamentum thin, translucent white, tegmental colouration shining through, especially in central part. Apophyses (Figs 2C, E) wide, triangular in valve ii to trapezoid in tail valve. Connected by jugal sinus. Insertion plates, short, slit formula: 13 / 1 / 14. Teeth somewhat rough on outside, with sharp edges, eaves spongy. Slit rays present in all valves (Fig. 3A).
Perinotum generally brighter coloured than tegmentum, with two whitish bands in the sutural region of valves vii–viii (Fig. 1 E), slightly darker transversal bands. Dorsally beset with smooth, inwardly directed, blunt spicules that measure 81– 91 x 16–18 µm (Figs 3B, C). Regularly spaced rows of cups (up to 4) that have long curved ringshaft needles, 405 µm in length (Fig. 3B). Dense fringe of sharply pointed, outward-directed spicules at margin, measuring 92–100 x 12–14 µm, the distal part with a delicate feather-like sculpture (Fig. 3B). Ventral scales radially arranged, smooth, broad-oval, obtuse, 47– 56 x 17–20 µm (Fig. 3D).
Radula (Figs 3E, F) 1.2 mm in length of which 0.5 mm is taken by radular cartilage. 35 rows of teeth, 26 mineralized. Central tooth short, stout, about 23 µm in length, maximal 16 µm wide at base, with tapered distal end and simple, slightly notched and irregular cutting edge. First lateral as long as central tooth, very wide with wing-like extension on lower inner half. Base of first lateral tooth slightly wider than distal end with bent cutting edge. Shaft of second lateral tooth 58 µm long, with distinct wing-like extension in upper half, cusp tridentate. Denticles of equal length, outermost appears widest. Major uncinal tooth simple flat, without supporting function.
There are 15 holobranchial ctenidia on both sides of the foot.
Comments: Kaas & Van Belle (1990) described the species on the basis of a slightly smaller specimen (6 mm). In contrast to the present material, the holotype shows more, slightly oblique sulci on the pleural areas, of which only the inner sulci do not reach the anterior valve margin, and their central and first lateral radula tooth illustrations are different. They illstrated the central tooth as ovoid, while it is only widened in the lower part in our material. Their figure of the first lateral tooth does not show the wings in the lower part as in our specimen and our examinations have shown that the first lateral is wider than Kaas & Van Belle (1990) illustrated. The latter may be an intraspecific variation as all other characters are also found in specimens from New Caledonia, which on the other hand show two incisions in the examined intermediate valves. Due to the small size of the holotype it also may be, that the differences in radula are a result of an underdevelopment stage. Apart from the slight differences of the sulci, the Fijian specimen do not differs from that from New Caledonia. It shows the same girdle ornamentation, have a common range of slit-numbers, and the tegmental sculpture is the same. The variability of the sulci is not unusual in Callochitons. Dell’Angelo & Smriglio (1999) demonstrated similar conditions for the type species, mentioning that the number of sulci ranges from 3 to 5 and also that only some of them may reach the anterior valve margin. This is the first record of the species from Fiji.
description: Published as part of Schwabe, Enrico, Sirenko, Boris I. & Seeto, Johnson, 2008, A checklist of Polyplacophora (Mollusca) from the Fiji islands, pp. 1-52 in Zootaxa 1777 on pages 9-10, DOI: 10.5281/zenodo.274284