Tonicia chilensis, (FREMBLY, 1827)

Ibáñez, Christian M, Eernisse, Douglas J, Méndez, Marco A, Valladares, Moises, Sellanes, Javier, Sirenko, Boris I & Pardo-Gandarillas, M Cecilia, 2019, Phylogeny, divergence times and species delimitation of Tonicia (Polyplacophora: Chitonidae) from the eastern Pacific Ocean, Zoological Journal of the Linnean Society 186 (4), pp. 915-933 : 923-925

TONICIA CHILENSIS ( FREMBLY, 1827)

( FIG. 4 )

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

Chiton fastigiatus Gray MS, Sowerby & Reeve, 1847 : pl. 5, sp. & fig. 26.

Tonicia chilensis de Castellanos, 1956: 478 , pl. 9; 1988: 23, figs 80–92. – Kaas et al., 2006: 297.

Tonicia elegans f. chilensis Leloup, 1956: 71 , figs 40, 41.

Tonicia fastigiata Leloup, 1956: 63 , figs 33–35.

Tonicia atrata Leloup, 1956: 59 , figs 30–32. – Powell, 1960: 125. – Dell, 1971: 221. – Leloup, 1973: 19. – de Castellanos, 1988: figs 93–95. – Götting, 1989: 55, 56. – Sirenko, 2006a: 85, figs 6–8. – Schwabe et al., 2006: 12 , figs 9–18. – Kaas et al., 2006: 301, fig. 122, map 55. – Schwabe, 2009: 409.

Type material repository: British Museum of Natural

History ( BMNH).

Type locality: Valparaiso, Chile .

Like T. calbucensis , T. chilensis consists of two morphologically different ecotypes. The northern ecotype of T. chilensis inhabits the coast of central Chile (~33– 39°S), whereas the southern ecotype of T. chilensis is found from Puerto Montt (~ 41°S) to Tierra del Fuego (~ 53°S). These two forms have several notable differences of tegmental sculpture and girdle features; as such, we describe each form separately.

Description of the southern ecotype of T. chilensis

Body large sized, up to 77 mm in length, elongated, oval ( Table 2), with solid valves moderately elevated (dorsal elevation 0.30–0.35), subcarinate and not beaked. Tegmentum colour variable, from dark green to blackish, often with pale greyish blotches or streaks; occasionally with some valves orange and black in others. Head valve semi-circular; hind margin widely V-shaped. Tegmentum has rare, very small granules, and most of these are arranged near the hind margin. Growth lines evident. Intermediate valves solid and broadly rectangular. Anterior margin almost straight in the central part; distinctly slants towards the rounded side margins. Hind margin concave at both sides of the slightly protruding apex. Lateral area not raised and sculptured like the head valve. Ocelli numerous and arranged in a random manner. Central area almost smooth or vaguely granulose. When present, small granules sometimes coalesce in short wrinkles in front of diagonal lines. Dorsal ridge very low and narrow, with a smooth keel in the middle and one to five longitudinal grooves on both sides. Tail valve as wide as the head valve or slightly narrower; front margin convex; mucro elevated subcentral or antemedian, elevated; antemucronal area sculptured like the central areas; postmucronal area sculptured like the head valve. Articulamentum white and blotched with brown in the central part of the valves. Apophyses large, rather wide, rounded, and connected across the narrow jugal sinus by a long dentate plate (13–24 denticles). Slit formula 7–9/1/9–13. Teeth short and deeply pectinated on the upper side and outer edge. Very wide girdle (ratio of the width of valve V to the width of the girdle is 2.1–2.7), nude to the naked eye and velvety. Dorsal side of the girdle black or dark green in live specimens and dirty yellow after fixation. Girdle covered with numerous short bristles and small, light, striated, flattened spicules ≤ 42 μm in length. Marginal edge with short bristles and rare spicules that are longer than the dorsal spicules. Ventral side of the girdle with radiating rows of rectangular scales ≤ 40 μm in length. Major lateral tooth of the radula has a unicuspid roundish head. Gills spanning from valve II to valve VIII, 38 on each side of specimens with body length of 44 mm.

Remarks

The southern ecotype of T. chilensis is easily distinguishable from the northern ecotype by having longer intermediate valves. The ratio of the width of valve V to the length is 1.8–2.1 (vs. 2.4–2.5 in the northern ecotype). It has two to six longitudinal ribs near both sides of the flattened keel in the jugal area (vs. more than ten ribs in the northern ecotype). The spicules are light (vs. dark in the northern ecotype), and it has small granules in the pleural and lateral areas. Specimens from the fjords in Golfo Ancud in southern Chile at depths of 6–19 m have tegmental structures that are more similar to the southern ecotype, but the lengths of the intermediate valves are shorter and the dorsal spicules of the girdle are dark, like those found in the northern ecotype. The correct identification of C. chilensis Frembly, 1827 (type locality Valparaiso, Chile) by previous authors and by us is further complicated by the lack of type material or even figures of the type material (see above).

Distribution: The southern ecotype of T. chilensis inhabits the coasts of southern Chile (Puerto Montt, ~ 41°S) to Tierra del Fuego, the Beagle Channel, the Strait of Magellan (~53– 54°S) and the Falkland Islands (Atlantic Ocean, ~ 41°S). It is found from the intertidal zones to depths of 36 m.

Description of the northern ecotype of T. chilensis

Body large sized, ≤ 81 mm in length ( Table 2), oval, very minimally elevated (dorsal elevation 0.25), rounded or slightly subcarinated. Side slopes straight; valves are slightly beaked in young specimens. Tegmentum streaked with various combinations of dark brown, yellow, reddish brown, black and red in small specimens with body lengths up to 20–25 mm. Large individuals uniformly black. Head valve semi-circular; hind margin slightly concave. Tegmentum sculptured with low pustules arranged without a definite pattern. Growth lines noticeable. Intermediate valves broadly rectangular; front margin slightly concave in jugum and convex in pleural parts. Hind margin weakly concave on both sides of the prominent pointed apex. Lateral area slightly raised and sculptured like the head valve. Central area with ten or more longitudinal ribs in the central part of the valve. Several low pustules run diagonally between the central and lateral area of small specimens. Tail valve is smaller than the head valve. The front margin is concave. Antemedian portion of mucro not raised; antemucronal area sculptured like the central area, and postmucronal area sculptured like the head valve. Articulamentum white, with lighter or dark reddish-brown parts in the apical area. Apophyses are wide and rather long. Outer half of the apophyses and teeth sharply pectinated. Sinus has a short, dentate (<15 denticles) jugal plate. Slit formula is 8/1/10. Girdle rather wide and spotted in young live specimens, black in adult specimens. After fixation, girdle becomes dirty yellow in colour and is dorsally covered with small, flattened spicules up to 23 µm × 18 µm. Marginal spicules twice as large as the dorsal spicules. Ventral side covered with radiating rows of subquadragular scales. The radula of a chiton with body length of 20.6 mm is 7.1 mm long and has 41 transverse rows of mature teeth. The central tooth is long, with a curved blade. The major lateral tooth is rounded, with a unidentate cusp. Fifty-three gills per side, extending from valve II to valve VIII in the same specimen.

Remarks

The northern ecotype of T. chilensis differs from other congeneric species by having ten or more longitudinal ribs on both sides of the jugum. The tegmentum and girdle are black, and the outer half of the apophyses and teeth are sharply pectinated.

Distribution: This form inhabits the coasts of central Chile from Ventanas (~ 33°S) to Valdivia (~ 39°S). It lives in the intertidal zone together with red and brown algae, coexisting with C. granosus near Valdivia and A. echinata and C. granosus near Las Cruces (~ 33°S).

Figures

Figure 4. Pictures oflive specimens ofTonicia.A,Tonicia chilensis (southern ecotype), Huinay (~41°S).B, Tonicia calbucensis (southern ecotype), Huinay (~41°S). C, Tonicia chilensis, Ventanas (~33°S). D, Tonicia disjuncta, Los Vilos (~32°S). E, Tonicia calbucensis (northern ecotype), Coquimbo (~29°S). F, Tonicia fremblyana, Arica (~18°S). G, Tonicia forbesii, Baja California (~24°N). H, Tonicia lebruni, Punta Arenas (~53°S). I, Tonicia disjuncta, Huinay (~41°S).