Dallina Beecher, 1893

Bitner, Maria Aleksandra, 2008, New data on the recent brachiopods from the Fiji and Wallis and Futuna islands, South-West Pacific, Zoosystema 30 (2), pp. 419-461 : 444-446

Genus Dallina Beecher, 1893

TYPE SPECIES. — Terebratula septigera Lovén, 1846 by original designation ( Beecher 1893: 382).

Dallina triangularis Yabe & Hatai, 1934 ( Fig. 16 B-G)

Dallina triangularis Yabe & Hatai, 1934b: 662 , figs 31-35. — Hatai 1940: 320, pl. 7, figs 22-27.

DEPTH RANGE. — 260-1226 m.

REMARKS

The investigated specimens correspond in size and outline with those described as Dallina triangularis from off Japan ( Hatai 1940). The shell is of medium size, thin, ventribiconvex, triangular in outline, widest at anterior part. The anterior commissure is broadly paraplicate. The beak is erect to suberect with a large, circular permesothyrid foramen. The symphytium is small. The ventral valve interior with small teeth without dental plates and very short pedicle collar. The inner and outer hinge plates are separated by distinct crural bases. The median septum is very long, high posteriorly and very low anteriorly. The loop is teloform, not attached to the septum, with long slender descending branches and broad ascending branches. The loops in the investigated specimens are so delicate that it has not been possible to remove the tissues without breaking the loop.

Dallina triangularis differs from other species occurring in the western Pacific, D. raphaelis (Dall, 1870) , D. obessa Yabe & Hatai, 1934 and D. elongata Hatai, 1940 , in being smaller, having triangular outline and thinner shell ( Hatai 1940; Foster 1989). Dallina obessa is also more convex.

The Miocene species Dallina vitilevensis Ladd, 1934 from Fiji is smaller than the investigated specimens and is more elongate ( Ladd 1934: pl. 24, figs 4-7). The systematic position of the Neogene specimens from Fiji assigned by Cooper (1978) to the genus Dallina is doubtful. Cooper (1978: pl. 1, fig. 26) observed well-developed dental plates which are absent, according to him, in larger specimens. Examination of early growth stages of the Dallina type species, D. septigera (Lovén, 1846) , confirms the absence of dental plates through all the stages of development (see MacKinnon & Lee 2006b: 2242), thus the specimens with dental plates cannot be assigned to Dallina .

Dallina triangularis is very rare in the Fiji collection and this is the first record of Dallina from off the Fiji Islands.

Figures

FIG. 16. — A, Septicollarina sp., Fiji, Lau Ridge, BORDAU 1, stn CP 1409, 557-558 m, dorsal view of complete specimen (MNHN BRA-3088); B-G, Dallina triangularis Yabe & Hatai, 1934, Fiji, Lau Ridge, BORDAU 1, stn CP 1409, 557-558 m, dorsal, lateral and anterior views of complete specimens (MNHN BRA-3109, 3110). Scale bar: A: 0.5 cm; B-G: 1 cm.