Amphithyris Thomson, 1918

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 : 440-442

Genus Amphithyris Thomson, 1918

TYPE SPECIES. — Amphithyris buckmani Thomson, 1918 by original designation ( Thomson 1918: 20).

Amphithyris buckmani Thomson, 1918 ( Fig. 11 )

Amphithyris buckmani Thomson, 1918: 22 , pl. 15, fig. 9; pl. 16, fig. 35. — Bitner 2006b: 28-30, fig. 6a-f.

MATERIAL EXAMINED. — Fiji. MUSORSTOM 10, Bligh Water, stn CP 1309, 11 complete specimens. — Stn DW 1314, 3 complete specimens. — Stn CP 1316, 1 complete specimen.— Stn CP 1330, 1 complete specimen.— Stn CP 1331, 143 complete specimens, 4 dorsal valves.— Stn CP 1332, 212 complete specimens, 1 dorsal valve.— Stn DW 1333, 5 complete specimens.— Stn DW 1334, 3complete specimens. — Stn CP 1335, 8 complete specimens. — Stn CC 1336, 6 complete specimens. — Stn CP 1341, 17 complete specimens. — Stn DW 1345, 3 complete specimens, 1 ventral valve. — Viti Levu, stn CP 1353, 36 complete specimens. — Stn CP 1354, 25 complete specimens. — Stn DW 1359, 2 complete specimens. — Stn CP 1360, 1 complete specimen. — Stn CP 1369, 7 complete specimens, 3 ventral valves, 2 dorsal valves.

BORDAU 1, Lau Ridge, stn CP 1392, 3 complete specimens. — Stn CP 1394, 1 complete specimen. — Stn CP 1396, about 160 complete specimens attached to the rock. — Stn CP 1398, 1 complete specimen. — Stn CP 1413, 2 complete specimens.

DEPTH RANGE. — 183- 963 m.

MEASUREMENTS. — See Table 14; see also Figure 12.

REMARKS

Amphithyris buckmani , already recorded from Fiji ( Bitner 2006b), is the commonest species (more than 600 specimens) in the studied material. This species is easily recognisable by its very small size, radially ornamented and convex ventral valve, smooth and flat dorsal valve, and large amphithyrid foramen.The specimens in the new material are slightly larger than those previously described from Fiji. The outline is very variable, from transversely oval to subcircular and subtriangular. The shell can be asymmetrical,

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depending in shape on the substrate ( Fig. 11F ) as A. buckmani lives closely attached to the substrate by a very short pedicle. The dorsal valve interior with high inner socket ridges and short, very low median septum. The schizolophous lophophore remains fused to the body wall ( Fig. 11K, L ).

Amphithyris buckmani differs from two known other Amphithyris species , A. hallettensis Foster, 1974 and A. richardsonae Campbell & Fleming, 1981 , in larger size and radial ornamentation of the ventral valve ( Foster 1974; Campbell & Fleming 1981).

Figures

FIG. 11. — Amphithyris buckmani Thomson, 1918, Fiji: A, B, inner views of ventral valves (MNHN BRA-3092, 3093); A, Bligh Water, CP 1332, 640-687 m; B, Viti Levu, MUSORSTOM 10, stn CP 1369, 392-433 m; C, D, inner and oblique views of dorsal valve (MNHN BRA-3094), Bligh Water, MUSORSTOM 10, stn CP 1332, 640-687 m; E, dorsal view of complete specimen (MNHN BRA-3095), Bligh Water,MUSORSTOM 10, stn CP 1331,694-703 m,visible young individual attached;F, G, dorsal views of complete specimens (MNHN BRA-3096,3097),Bligh Water,MUSORSTOM 10,stn CP 1332,640-687 m; H, I, dorsal view of complete specimen (MNHN BRA-3098) and enlargement of posterior part, Bligh Water, MUSORSTOM 10, stn CP 1332, 640-687 m; J, ventral view of complete specimen (MNHN BRA-3099), Bligh Water, MUSORSTOM 10, stn CP 1309, 843-887 m; K, L, Inner view of dorsal valve (MNHN BRA-3100) with preserved schizolophous lophophore and enlargement of lophophore, Bligh Water, MUSORSTOM 10, stn CP 1331, 694-703 m. All SEM. Scale bars: A, B,E-H, 2 mm; C, D, J-L, 1 mm; I, 500 μm.

FIG. 12. — Intraspecific variation in Amphithyris buckmani Thomson, 1918. Scatter diagram plotting length/ width. N, number of specimens.