Tonicia calbucensis Plate 1897

Tonicia calbucensis Plate, 1897

(Figures 10, 16, 21–30)

Tonicia calbucensis Plate, 1897: 205 –207, pl. 12, fig. 134; Nierstrasz 1905: 98; 1906: 150; Thiele 1908: 21; Boudet Rommel 1945: 127; Carcelles & Williamson 1951: 249; Castellanos 1956: 478, pl. 9; 1988: 22, figs. 71–73; Leloup 1956: 78; Kaas & Van Belle 1980: 20; 1998: 37; Kilias 1995: 158 (lectotype designation); Slieker 2000: 140; Sirenko & Gallardo 2005: 89; Sirenko 2006b: 85, fig. 10.

Tonicia lebruni var. calbucensis; Forcelli 1999: 186, illustrated.

Size: Maximum length 40 mm (Forcelli 1999). Body outline: Elongate oval, moderately elevated, subcarinated to slightly keeled (Figures 21–23). Color: Orange brown to brownish red with darker radial streaks on terminal valves and lateral areas, on central areas these streaks orientated longitudinally. Jugal area in general chestnut brown with two wider white streaks on both sides (Figures 21–26). Valves: Solid and smooth except for faint growth marks arranged commarginally, more distinct at valve margins. Small granules partly extending along diagonal ridge. Head valve (Figure 24) semicircular with wide V­shaped posterior margin, weakly notched in middle. Intermediate valves rectangular, straight posterior and anterior valve margins parallel, but anterior valve margin extends anteriorly in valve ii. Apices slightly protruding. Lateral areas slightly elevated and clearly indicated by different arrangement of brownish streaks, radially in lateral areas, longitudinally in pleural areas (Figure 25). Semicircular tail valve (Figure 26) with narrow antemucronal area, mucro elevated but directed backward. Mucro situated in front of valve middle. Postmucronal slope steep and straight. Ocelli on radial streaks of lateral areas and terminal valves only (not in white zones in between). Articulamentum: White and strongly developed. Centrally with a brownish spot. Apophyses solid, moderately large, triangular on valve ii, rectangular­trapezoidal on remaining valves (Figures 25–26). Apophyses connected by short sawed jugal sinus, laterally deeply notched. Slit formula: 8 / 1 / 8 (9 / 1 / 9 in original description), teeth rather short but wide. Teeth strongly pectinated on outside. Slit rays present in all valves. Perinotum: Very wide and fleshy. Dorsally covered with minute conical spicules (appears naked), which are smooth and sharp­pointed, round in cross section (Figures 27–28). Ventrally with radial rows of roundish to squarish scales, rounded at their free end. Scales not imbricated. Radial rows always interrupted. Scale arrangement resembles that of short pearl necklets (Figure 29). Ctenidia (specimen 28.8 mm body length): 41 ctenidia on each side of foot, arranged holobranchilly and adanally, group of largest ctenidia situated beneath valves vivii. Radula (same specimen): Radula length 9.4 mm, radula cartilage 2.9 mm in length; 66 teeth rows, 55 already mineralized. Central tooth slightly depressed in middle, slender, with simple inward­directed blade. First lateral tooth elongate, widened at base, on its upper end directed inward with simple blade, latter slightly notched in middle. Head of second lateral tooth discoidal, with slightly extended side margins and obtusely pointed tip of cutting edge. Major lateral tooth spoon­shaped and smooth (Figure 30).

Material: Thirty­four specimens were collected from 4 stations within the fjord, covering a bathymetric range from 5 to 30 m depth (see Table 1).

Distribution: Tonicia calbucensis occurs from Puerto Montt southwards to Punta Arenas in the Straits of Magellan, from 0 to 35 m depth (Thiele 1908).

Remarks: Besides the specimens cited above, and the lectotype (Natural History Museum Berlin [ZMB] Moll 102.006, Figures 21–23), material from additional localities between Puerto Montt and Punta Arenas (ZSM) was examined. Specimens from the samples observed showed consistent valve shapes and shell coloration.

Tonicia calbucensis was synonymized with Tonicia lebruni de Rochebrune, 1884 (Figure 20) by Leloup (1956). He interpreted a small specimen of T. lebruni with similar coloration, perinotum elements and radula to refer to Tonicia calbucensis. External examination of two dry, flat preserved syntypes of T. lebruni (Muséum National d'Histoire Naturelle, Paris, France [MNHN]) show them to reach approximately 48 mm in length, having all valves in situ, and being chestnut with a shiny surface. Comparison between type samples of T. calbucensis (Figures 21–23) and T. lebruni (Figure 20) reveals a number of differences: 1) the head valve has a much steeper slope in T. lebruni, 2) the apices in T. calbucensis are hardly protruding in the first two intermediate valves, while they protrude in all valves of T. lebruni, 3) dorsally T. calbucensis is more carinated than T. lebruni, 4) the lateral areas are defined more clearly in T. lebruni and have an anteriorly shallow slope, while the diagonal ridge in T. calbucensis is elevated immediately above the anterior slope, 5) T. lebruni has uniformly commarginal striations on the central area, while this region is longitudinally striated in T. calbucensis, 6) the postmucronal slope appears lesser steep in T. calbucensis. These characters are consistent with the newly collected specimens, and intermediate forms were not observed. This leads us to reinstate T. calbucensis as distinct from the sympatric T. lebruni. Sirenko (2006b) also underscored valve and perinotum characters and came to the same conclusion.