Choneplax littlerorum Sirenko, 2003

Schwabe, Enrico, Sirenko, Boris I. & Seeto, Johnson, 2008, A checklist of Polyplacophora (Mollusca) from the Fiji islands, Zootaxa 1777, pp. 1-52 : 35-39

Choneplax littlerorum Sirenko, 2003

( Figures 8 C–F, 9A–F, 10A–F, 11A–D)

Choneplax littlerorum Sirenko 2003: 33 ; figs, 1A–H, 2, 3, 4A–C; 2006: 38, fig. 8B; Schwabe 2005b: 97.

Locus typicus: American Samoa: Tutuila Island: Pago Pago Harbour, Goal Is. Point (14°16.659'S 170°40.926'W), 3–5 m, on crustose coralline algae.

Primary type: Holotype (ZISP 203/2150).

Type (s) without name-bearing function: Two paratypes ( ZISP 204/2151), one paratype ( USNM).

Material examined: ZSM Mol 20061626: 2 subadult spms, 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, out side of the fringing reef, in deep channels with strong currents, in pieces of dead corals encrusted with coralline red algae, 3– 4 m, leg. Enrico Schwabe, 29 August 2006, wet; ZISP: 1 subadult spm, Vekai Island [17°34’S 178°49’W], Callisto St. 94, 8 m, leg. Boris I. Sirenko, 0 8 February 1975, wet; ZISP: 1 adult spm, Cicia Island [17°45'S 179°18'W], Callisto St. 83, 0.3m, leg. Boris Sirenko, 0 6 February 1975, wet; ZSM Mol 20062094: 1 valve, Viti Levu, Laucala Bay, west and north side of Nukumbutho Island 18°10.474'S 178°28.343'E; extracted from sand, collected in 1 m, leg. Enrico Schwabe, 21 August 2006, dry; ZSM Mol 20062136: 50 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, different algae, from the reef flat, at extreme low tide, extracted from sand between the algae, 0.5– 1 m, leg. Enrico Schwabe, 29 August 2006, dry; ZSM Mol 20070108: 5 subadult spms + 1 valve, 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, among algae from the reef pools, 0.5–1.5 m, leg. Michael Schrödl,

Enrico Schwabe & Andreas Altnöder, 24 August 2006, wet; ZSM Mol 20070136: 1 juvenile spms, Viti Levu, Laucala Bay, north side of Makuluva Island 18°11.250'S 178°30.992'E, in fine coral sand, 0–1 m, leg. Enrico Schwabe, 21 August 2006, wet.

Habitat: The species inhabits crevices and holes of dead coral pieces, mainly encrusted ones.

Distribution: The species was known from the Samoan Islands only (Sirenko 2003). This is the first record for Fiji.

Remarks: The identification of this species is somewhat questionable. While the isolated valves undoubtly belong to this species, the animals are identified as this species with some hesitation. The species was originally described on the basis of four specimens of which the smallest was about 7.5 mm. Our material consists of smaller animals, the largest of the ZSM specimens (here used for the SEM study) measuring ca. 5 mm (ZSM Mol 20061626). The specimen shows two clear incisions in the tail valve and was tentatively identified as Acanthochitona sp. The single specimen from the ZISP collection, labeled as Notochiton sp. is only 3 x 1.7 mm in size with 6 ctenidia, of which the posteriormost is the largest. This specimen was certainly fixed with formaldehyde. Dorsal perinotum elements are nearly completely etched away and those from the ventral side are only partly available. The valves are so corroded that they were broken while being prepared for a SEM analysis. Most important, the tuftpores show only remnants of the needles. After examination of the radula by SEM (1.3 mm in length, radular cartilage 0.5 mm, 42 teeth rows, 33 rows mineralized) and a few ventral perinotum elements, ES considers this specimen conspecific with the specimens from the ZSM, one of which is illustrated here in detail ( Figs 9–11 ).

The animal is about 5 mm in length, elongate, with 18 tufts (four in the head area and additionaly one per suture), with seven ctenidia of which the largest is the posteriormost, mantle fold short and nearly semicircular. Valves with a smooth jugal area, pleurolateral areas with round granules with central aesthetes. Head valve with five slits, intermediate valve with a small slit and tail valve with two lateral, forward directed slits. Slitrays present underneath the jugal area, the brownish articulamentum is very porous. Radula is 1.7 mm in length, 1.1 mm of which is taken up by the radula cartilage; with 41 teeth rows of which 34 are mineralized. The smallest available tail valve of Choneplax littlerorum (ZSM Mol 20062136) is here shown ventrally ( Fig. 8 F). Clearly visible are the remnants of slits and so it is not unlikely that smaller tail valves of this species have a different (originally described with no slits in the tail valve), more Acanthochitona -like tail valve as presented here ( Figs 9F , 10A ). The articulamentum is brownish in typical valves of Choneplax littlerorum and also in the Acanthochitona -like small specimens illustrated here. The composition, form and size of the perinotum elements ( Figs 10B–F , 11A, B ) and the slender central tooth with the forward directed blade, together with the S-shaped form of the first lateral tooth ( Figs 11C, D ) of the small specimens do not differ from the original description of Choneplax littlerorum . Summarized, the overall tegmentum granulation, the colouration of the articulamentum, the shape of the flattened valves, the perinotum ornamentation, and the radula characteristics correspond to the type material. The only difference we recognized are the two slits in the tail valve in the present material compared to the slit-less tail valve of the somewhat larger specimens of the type series. That is why we consider the small specimens juveniles of Choneplax littlerorum , but are aware that only intermediate growth stages or a genetic analysis will allow more certainty about this assignment.

Figures

FIGURE 8. A – B, Cryptoplax sp., SMNH 87439 (photo: Purba Pal / SMNH, © All rights reserved), Viti Levu, Namuka [17 ° 59 ’ S 178 ° 36 ’ E], dorsal view. A, complete specimen. B, detail of the intermediate valves. C – F, Choneplax littlerorum Sirenko, 2003. C, “ Acanthochitona sp. ”, ZSM Mol 20061626: Fiji, 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, dorsal view. D, same specimen as in fig. C, but alive, photo taken through the microscope. E, “ Notoplax sp. ”, ZISP: Fiji, Vekai Island [17 ° 34 ’ S 178 ° 49 ’ W], Callisto St. 94, dorsal view. F, Choneplax littlerorum Sirenko, 2003, ZSM Mol 20062136: Fiji, 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, ventral view of a tail valve, sl indicates the position of the incisions [slits]. Scale bars A 2 mm, B – E 1 mm, F 100 µm.

FIGURE 9. A – F, Choneplax littlerorum Sirenko, 2003. A – D, ZSM Mol 20062136: Fiji, 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. A, left lateral view of a tail valve, sl indicates the position of the incisions [slits]. B, detail of the antemucronal area. C, dorsal view of an intermediate valve. D, ventral view of an intermediate valve. E – F, “ Acanthochitona sp. ”, ZSM Mol 20061626: Fiji, 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. E, dorsal view of the head valve. F, dorsal view of the tail valve. Scale bars A, C, D 500 µm, B 50 µm, E, F 200 µm.

FIGURE 10. A – F, Choneplax littlerorum Sirenko, 2003, “ Acanthochitona sp. ”, ZSM Mol 20061626: Fiji, 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. A, left lateral view of the tail valve, sl indicates the position of the incisions [slits]. B, dorsal perinotum elements, showing the tuft pore. C, isolated needles from the tuft. D, E, dorsal perinotum elements in situ. F, spicules from the marginal fringe. Scale bars A 200 µm, B, F 50 µm, C, 100 µm, D, E 10 µm.

FIGURE 11. A – D, Choneplax littlerorum Sirenko, 2003, “ Acanthochitona sp. ”, ZSM Mol 20061626: Fiji, 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. A, spicules from the marginal fringe. B, ventral perinotum elements. C, anterior portion of the radula. D, close up of fig. E to show the central and first lateral teeth. Scale bars A – C 50 µm, D 10 µm.