Placiphorella sp.

Sellanes, Enrico Schwabe Javier, 2010, Revision of Chilean bathyal chitons (Mollusca: Polyplacophora) associated with cold-seeps, including description of a new species of Leptochiton (Leptochitonidae), Organisms Diversity & Evolution (New York, N. Y.) 10 (1), pp. 31-55 : 48

Placiphorella sp.

( Figs. 14I, J , 15 )

Chilean deep-water records Sellanes et al. (2004: 1066; as “ Placiphorella sp. nov. ”): from 934 m, off Concepción (36º21′S 73º44′W). — Sellanes et al. (2008: 1105; as “ Placiphorella atlantica ”): see “Material examined” below.

Material examined 3 spms ( ZSM Mol 20080794 + 20080824) Chile, NW off Concepción (36º00.23′S 73º38.41′W), 922 m ; 9 spms ( JS) Chile, NW off Concepción (36º00.23′S 73º38.41′W), 922 m ; 1 spm ( ZSM Mol 20041044) from Chile, off Concepción , 36°21′S 73°44′W, 870–930 m.

Remarks This species was first mentioned from a methane seep area by Sellanes et al. (2004). Since then, Saito et al. (2008) have described Placiphorella isaotakii , which was collected at the Yaeyama Islands, also from a methane seep area, and P. okutanii from a potential hydrothermal region near the Izu-Ogasawara Islands. Both species were regarded as possibly only guests in those habitats. The considerable number of specimens of the present species leads us to hypothesize that it is closely associated with, if not endemic to, the vicinity of the CMSA site. Our SEM images ( Fig. 15 ) show close similarity to Placiphorella okutanii , but also distinct differences at least in the form of the tail valve (shorter in length relative to width in the present material). Our material may represent an undescribed species and is currently under study by Dr. Boris Sirenko (ZISP). A comparison with digital images of the holotype of Placophora (Euplacophora) atlantica ( Fig. 14K, L ; see preceding species) shows considerable differences in the shape of the tail valve. To make identification easier, SEM images of the girdle and the radula are also provided.

Figures

Fig. 14 Ischnochitonid, chitonid and mopaliid deep- water Polyplacophora from Chile. (A–F) Tripoplax cowani, adult, ZSM Mol 20080792 (A, B), and juvenile, ZSM Mol 20080793 (C–F): (A) valves i–v; (B) valves vi–viii; (C, D) dorsal views of anterior and posterior portions, respectively, of complete specimen; (E) left lateral view of complete speci- men; (F) left lateral view of posterior portion, showing post- mucronal slope of tail valve. (G) Tonicia disjuncta, ZSM Mol 20061008; dorsal view of com- plete specimen. (H) Plaxiphora aurata, ZSM Moll 20040961; complete specimen in situ (Chile, Punta Huinay, 42º22.483´S 072º25.693´W, 0– 30.5 m), body length c. 24 mm. (I, J) Placiphorella sp., ZSM Mol 20041044; dorsal views: (I) complete specimen; (J) isolated tail valve. (K, L) Placophora (Euplacophora) atlantica, holo- type; dorsal views: (K) complete specimen; (L) isolated tail valve. Scale bars: A, B, I, K=10 mm; C–E=5 mm; F, L, J=2 mm; G=20 mm. (K, L) courtesy of Y. Villacampa

Fig. 15 Scanning electron micrographs of Placiphorella sp., ZSM Mol 20041044. (A, B) Perinotum spicules in situ. (C) Ventro-marginal girdle elements, in situ. (D) Bristle, view from ventro-marginal side of girdle. (E) Spicules of precephalic ten- tacles, in situ. (F) Anterior por- tion of radula. Scale bars: A=50 µm; B–F=100 µm