Thecidellina Thomson, 1915

Bitner, Maria Aleksandra, 2007, Recent brachiopods from the Austral Islands, French Polynesia, South-Central Pacific, Zoosystema 29 (3), pp. 491-502 : 498-499

Genus Thecidellina Thomson, 1915

TYPE SPECIES. — Thecidium barretti Davidson, 1864 by original designation ( Thomson 1915: 462).

Thecidellina maxilla ( Hedley, 1899) ( Fig. 3 A-H; Table 3)

Thecidea maxilla Hedley, 1899: 508-510 , fig. 57.

Thecidellina maxilla – Dall 1920: 283. — Thomson 1927: 140. — Cooper 1954: 317, pl. 81, figs 1-10. — Zezina 1985: 208. — Laurin 1997: 453, 454, fig. 40A, B. — Lee & Robinson 2003: 350-352, figs 28-35.

Thecidellina cf. T. maxilla – Cooper 1964: 1118, pl. 301, figs 15, 16, 18, 19.

MATERIAL EXAMINED. — Austral Islands. Tubuai, BENTHAUS, stn DW 1955, 2 complete specimens. — Stn DW 1956, 3 complete specimens. — Stn DW 1958, 2 complete specimens. — Stn DW 1961, 4 complete specimens. — Arago Bank, stn DW 1968, 2 complete specimens. — Stn DW 1969, 1 complete specimen. — Stn DW 1978, 2 complete specimens. — Rurutu, stn DW 1998, 1 complete specimen. — Stn DW 2001, 4 complete specimens. — Stn DW 2002, 4 complete specimens, 1 dorsal valve. — Stn DW 2003, 1 complete specimen, 2 ventral valves. — Stn DW 2004, 2 complete specimens. Several complete specimens include soft parts.

DEPTH RANGE. — 80- 990 m.

MEASUREMENTS. — See Table 3.

DESCRIPTION

The shell is small (maximum length 7.0 mm), variable in outline from nearly circular to subtriangular, with a smooth surface ornamented only by numerous growth lines. The ventral valve has a triangular, flat interarea marked only by subparallel growth lines; there is no trace of a pseudodeltidium. No ventral median septum is present. The hemispondylium has two slender prongs extending anteriorly. The dorsal valve possesses a prominent, trilobed cardinal process and long straight median septum. Interior margin strongly tuberculate.

REMARKS

Although not the most common species in the investigated material, Thecidellina maxilla was found in the largest number (12) of stations. This species is widely distributed in the Pacific ( Cooper 1954, 1964; Zezina 1985; Laurin 1997; Lee & Robinson 2003; Bitner 2005), being known from the Miocene. The specimens of Thecidellina described by Cooper (1978) from the Miocene of Java and Fiji, and from the Pleistocene of Vanuatu are very similar to T. maxilla , and might be conspecific with the latter species (see also Lee & Robinson 2003).

The species Thecidellina japonica (Hayasaka, 1938) described from off Japan ( Hatai 1940) displays a great similarity to T. maxilla , suggesting that those two species are conspecific (see discussion in Lee & Robinson 2003: 355).

Figures

FIG. 3. — A-H, Thecidellina maxilla (Hedley, 1899); A, dorsal view of complete specimens attached to each other (MNHN BRA-3051), Ruturu Island,stn DW 2001, 200-550 m; B, C, inner view of ventral valve (B) and tilted (C) to show hemispondylium (MNHN BRA-3052), Ruturu Island, stn DW 2003, 250-330 m; D, E, inner view of dorsal valve (D) and posterior view (E) to show trilobed cardinal process (MNHN BRA-3053), Ruturu Island, stn DW 1998, 250-302 m; F, inner view of dorsal valve (MNHN BRA-3054), Arago Bank, stn DW 1978, 120-180 m; G, H, dorsal and lateral views of complete specimen (MNHN BRA-3055), Ruturu Island, stn DW 2001, 200-550 m; I, J, Megerlia truncata (Linnaeus, 1767), ventral and dorsal views of complete specimen (MNHN BRA-3050), Ruturu Island, stn DW 2009, 320-450 m. All SEM. Scale bars: A-C, F-J, 2 mm; D, E, 1 mm.