Tonicia chilensis ( Frembly, 1827 )

Schwabe, Enrico, Försterra, Günter, Häussermann, Verena, Melzer, Roland R. & Schrödl, Michael, 2006, Chitons (Mollusca: Polyplacophora) from the southern Chilean Comau Fjord, with reinstatement of Tonicia calbucensis Plate, 1897, Zootaxa 1341, pp. 1-27 : 15-16

Tonicia chilensis ( Frembly, 1827) sensu lato

( Figures 8 , 11, 17)

Chiton chilensis Frembly, 1827: 204 –205, suppl. pl. 17, fig. 8.

rather low elevated and subcarinated. Color: Variable, generally pale pinkish, yellowishorange to brownisch tones occur, interrupted by darker maculations on some specimens. Valves: Head valve semicircular with straight posterior valve margin unnotched in middle. Intermediate valves rectangular with concave posterior valve margin at both sides of protruding valve margin. Lateral areas slightly elevated and jugal area with more or less distinct keel. Tail valve nearly elliptical; central mucro slightly elevated and directed forward. Postmucronal area straight and moderately steep. Valves sculpture consisting of growth marks on terminal valves and lateral areas; micro­granulation on all valves becoming more distinct towards outer margins (especially in lateral areas), more or less faint striation in central areas. Ocelli occurring over terminal valves and from diagonal ridge to middle part of lateral areas. Articulamentum: White and solid, forming well developed insertion plates and round to trapezoidal apophyses; latter connected by denticulated, laterally deeply notched jugal plate. Slit formula: 9 / 1 / 11. Slit rays present in all valves. Teeth long and wide, strongly pectinated at outside. Perinotum: Thick cuticle with randomly arranged, short, deeply embedded scale­like spicules of different sizes. Ventrally, radial rows of short, thickset, more or less pointed scales with faint striation. Slender spicules of different sizes along margin. Radula (ZSM Moll 20034137, specimen 29 x 16 mm in size): 10.7 mm radula length, 5.3 mm radula cartilage. 64 teeth rows, 52 with mineralized teeth. In general, radula resembling T. calbucenis , with following exceptions: first lateral tooth lacking wing­like extensions covering central tooth; cutting edge of second lateral tooth more thickened, tip more pointed in middle; major uncinal tooth more thickset. Ctenidia (same specimen): 37 holobranchial and adanal ctenidia on each side of foot.

Material: Twenty­one specimens were collected from 6 stations (see Table 1 ). In the investigated area the species was found in depths between 5 and 28 m.

Distribution: Tonicia chilensis occurs from Perú southwards to Tierra del Fuego, with a former known bathymetric range from 0–15 m ( Leloup 1956, Reid & Osorio 2000).

Remarks: The list of nominal species that are united under Tonicia chilensis , as either subspecies, forms, or synonyms, is extensive ( Leloup 1956, Forcelli 1999, Kaas & Van Belle 1998). The type material of T. chilensis was not located together with the other Frembly types [personal communication, Kathie Way, Natural History Museum, London, March 2006]. Specimens from the coast between Callao, Perú and Valparaiso, Chile, the type locality, were not available to the authors. Thus, the identification of specimens from Comau can only be tentative, since the genus Tonicia , especially T. chilensis , is in urgent need of revision.

One of the specimens (ZSM Moll 20050025) was found close to an underwater spring with sulphurous water and was partly covered by aggregations of filamentous bacteria ( Figure 8 ). Results of a forthcoming stable isotope analysis of this specimen will show whether the bacteria live around and on the chiton , or whether the chiton was feeding on it.

Figures

FIGURE 8. Underwater photograph of a bacteria mat at an underwater spring with sulphurous water at station 3, the upper chiton is Tonicia chilensis (Frembly, 1827) (ZSM Moll 20050025) illustrated specimen measures 17.3 mm in length, the lower Chiton magnificus Deshayes, 1827 (ZSM Moll 20050026) illustrated specimen measures 15.6 mm in length. 9. Underwater photograph of Tonicia atrata (Sowerby, 1840) in situ (ZSM Moll 20050020) at station 3, illustrated specimen measures c. 30 mm in length. 10. Underwater photograph of Tonicia calbucensis Plate, 1897 in situ (NRS). 11. Underwater photograph of Tonicia chilensis (Frembly, 1827) in situ (NRS) at station 7. 12. Underwater photograph of Tonicia smithi Leloup, 1980 in situ (ZSM Moll 20050012) at station 12, illustrated specimen measures c. 50 mm in length. 13. Underwater photograph of Plaxiphora aurata (Spalowsky, 1795) in situ (ZSM Moll 20034100) at station 7, illustrated specimen measures c. 28 mm in length.