Tonicia calbucensis Plate, 1898

Sirenko, B. I. & Ibáñez, C. M., 2023, Comparative morphology of Tonicia (Polyplacophora) geographical ecotypes from Southeastern Pacific, Ruthenica, Russian Malacological Journal (Cambridge, England: 2003) 33 (1), pp. 27-45 : 29-31

Tonicia calbucensis Plate, 1898

Complete synonymy in Ibáñez et al., 2019.

Description of T. calbucensis southern ecotype

( Figs 1C, D; 2–4 )

The animals are of medium size, up to 40 mm long ( Table 2). Valves subcarinated, side slopes minimally convex with low elevation (dorsal eleva- tion 0.28). Tegmentum orange brown to brownish red with darker radial streaks on the terminal valves and lateral areas; central areas with streaks oriented longitudinally. Jugal area chestnut brown in general with two wider white streaks on both sides [after Schwabe et al., 2006]. Specimens collected near Punta Huinay (42.36°S, 72.44°W) and Isla Lili- huapi (42.16°, 72.59°W) have typical coloration or have yellow orange tegmentums and girdles. Head valve semicircular, and the posterior margin widely V-shaped. Intermediate valves broadly rectangular, and anterior margin almost straight in the central part and somewhat slanting towards the rounded side margins. Posterior margin straight, not beaked, and lateral areas not raised. Tail valve small and slightly narrower than head valve, mucro antemedian, antemucronal, and post mucronal slopes straight. All areas of tegmentums smooth with exception of 1–4 weak, short, narrow grooves on both sides of the jugum and several growth lines and ocelli. Ocelli on radial streaks of lateral areas and terminal valves only, not numerous.Articulamentum well developed with wide and rather long apophyses connected by a slightly dentate jugal plate. Slit formula 8/1/8, and teeth strongly pectinated on the outside. Girdle rather wide and leathery, usually rose with spots or rare orange in specimens with orange tegmentum, dorsally covered with rare small elongate sharppointed spicules and rare short bristles. Ventral side with radial rows of squarish scales. Specimens with a body length ~ 20 mm have a ~ 7.5 mm long radula, with 43 transverse rows of mature teeth. Central tooth narrows with a long curved blade. Major lateral tooth with unicuspid rounded head. From valve II to valve VIII, there are 34 gills on each side of specimens with body lengths of ~ 20 mm .

Description of Tonicia calbucensis northern ecotype ( Figs 1A, B; 5–10)

Body length medium sized, up to 50 mm, elon- gated and oval with low elevation (dorsal elevation 0.24–0.26). Valves minimally beaked ( Table 2). Tegmentum very variable in color and streaked with various combinations of dark brown, buff, yellow, pale, reddish brown, and wine red. Tegmentum and girdle are both rare uniform orange in alive specimens. Head valve semicircular, widely V-shaped posterior margin. Intermediate valves broadly rectangular. Ratio of the width of valve V to its length is 2.7–3.0. Anterior margin slightly concave in the jugal area and slanted at the pleural. Posterior margin weakly concave at both sides of the prominent pointed apex. Tail valve slightly less wide than the head valve.Antemedian portion of mucro not raised, antemucronal slope straight or slightly convex and postmucronal slope concave. Tegmentum sculptured with numerous granules or pustules and longitudinal grooves. Head valve, lateral area, pleural area, and postmucronal area sculptured with small granules or pustules. Pleural area with low granules arranged in longitudinal rows, become obsolete in some specimens. Both sides of the jugum have 1–3 longitudinal grooves that reach the anterior margin.Articulamentum white with all valves having a reddish spot in the apical area and in the center of the valve.Apophyses wide, rounded, and connected to the dentate jugal plate. Slit formula is 8/1, rarely 2/9–10. Slit rays are hardly noticeable. Girdle moderately wide and spotted in live specimens, uniformly yellow in fixed specimens. Girdle dorsally beset with few calcareous spicules up to 34 x 16 µm. Ventral side of the girdle covered with radiating rows of subquadrangular scales 35 x 17 µm. Radula of specimens with body lengths of 17.5 mm are 6.7 mm long, with 40 transverse rows of mature teeth. Central tooth narrows to a long curved blade, major lateral tooth has a unicuspid rounded head. There are 43 gills on each side of specimens with body lengths of 17.5 mm; spanning from valve II to valve VIII.

There are intermediate forms with a coloration similar to that of the northern ecotype, but with rare grains on tegmentum, as well as with an almost completely smooth shell in Metri Bay and Isla Lilihuapi, Golfo de Ancud.

The northern ecotype differs from the southern ecotype of Tonicia calbucensis by having smooth tegmentum without granules except several narrow, short, weak longitudinal grooves on both sides of the jugum and does not have bristles.

Figures

FIG. 2. Tonicia calbucensis, southern ecotype, South Chile, 42°22’S, 72°25’W, 5–20 m, BL 20.5 mm, 04.01.2005, leg. B. Sirenko. A. Valve I, dorsal view. B. Valve V, dorsal view. C. Valve VIII, dorsal view. D. Valve VII, detail of tegmentum in central area. E. Valve VII, rostral view. F. Valve VIII, lateral view.