Terebratulina austroamericana Zezina, 1981

Araya, Juan Francisco & Bitner, Maria Aleksandra, 2018, Rediscovery of Terebratulina austroamericana Zezina, 1981 (Brachiopoda: Cancellothyrididae) from off northern Chile, Zootaxa 4407 (3), pp. 443-446 : 444-445

Terebratulina austroamericana Zezina, 1981 ( Figs. 1A–1E , 2A–2D )

1892 Terebratulina crossei Davidson—Fischer and Oehlert , pp. 257–264, pl. 8, figs. 1–8.

1981 Terebratulina austroamericana Zezina , p. 155–157, figs. 1a, 1b.

Material examined. One live specimen, entangled in long-lines, off Caldera (26°42’00” S; 71°08’00” W), Región de Atacama, Chile, at about 2000 m depth, FV Juan Antonio (Caldera), 20 March 2015 ( MPCCL 16112015 ).

Description. Shell large (L= 35.4 mm, W= 36.1 mm, T= 14.0 mm; Figs. 1A–E ), thin, translucent, whitish in color, strongly punctate ( Fig. 2A ). Shell outline circular, length almost equal to width, maximum width near mid-length; lateral and anterior margins rounded, apical angle about 110°. Shell slightly ventro-biconvex (see Fig. 1D ), dorsal valve damaged in present specimen ( Fig. 1A ). Lateral commissure nearly straight, forming an angle around 120° with the anterior edge of the beak; anterior commissure rectimarginate. Beak short, rounded, suberect, foramen slightly attrite, large, circular, permesothyrid with minute, rudimentary disjunct deltidial plates. Pedicle wide and short, distally divided into rootlets ( Fig. 2B ). Shell surface of both valves covered with numerous ribs of rounded-triangular section with intercalated intermediate ribs up to fourth order ( Fig. 2C ). Some additional ribs bifurcate towards anterior edge; about 100 fine ribs present at edge of ventral valve, giving border a minute crenulation. Uneven, fine commarginal growth lines cross radial ribs. Ventral valve with a sub-circular (or sub-elliptical) convexity in lateral view ( Fig. 1D ), but with a clearly regular parabolic outline in posterior or anterior views ( Fig.1 , C, E); dorsal valve slightly convex in lateral view ( Fig. 1D ). Ventral valve interior with small hook-like teeth, pedicle collar short. Muscle scars not evident in examined specimen. Crura long and thin. Loop broken, with only wide, flattened dorso-ventrally descending branches preserved ( Fig. 2D ); during removal of soft body a broad transverse band became detached.

Distribution. Known previously from a single specimen collected off Valparaíso, central Chile, at 700 m depth; this species may also be distributed south to the Straits of Magellan, in 18–700 m ( Zezina 1981, 2010). Now recorded from northern Chile, with a depth range of 18 to 2000 m.

Remarks. In the original description of the species ( Zezina 1981), the holotype was illustrated only by line drawings of the brachial skeleton, and details of the exterior ribbing and general shell morphology were not illustrated. The present specimen confirms the status of this species, whose type material suggested to Cooper (1982) that it may represent a young individual of Terebratulina kiiensis Dall and Pilsbry, 1891 . This close similarity was also mentioned by Zezina (2010) who suggested that T. austroamericana may possibly be a geographical subspecies of the widespread species T. kiiensis . Details of the shell indeed suggest relationship with T. kiiensis ; however, the studied specimen differs in several characters (e.g. foramen size, apical angle, outline of shell) from the description of T. kiiensis given by Cooper (1982). The present specimen is also considerably larger than the holotype (36.1 mm x 35.4 mm versus 17 mm x 16 mm). However, in other details it is consistent with the original description of T. austroamericana .

This work adds to the scarce information on brachiopods from the Peruvian province; the present record from northern Chile extends the biogeographical range of this species significantly northwards and suggests a continuous distribution of this species along the Chilean continental margin.

Figures

FIGURE 1. Terebratulina austroamericana Zezina, 1981, conjoined shell. A. Dorsal view. B. Ventral view. C. Anterior view. D. Lateral view.E.Posterior view.

FIGURE 2. Terebratulina austroamericana Zezina, 1981, A. Detailof puncta on the external surface of the dorsal valve, B. Detail of foramenand pedicle,C.Detail of ribornamentation, D.oblique viewof crura and fragmentof the loop.