Eucalathis malgachensis, Bitner & Logan, 2016

Bitner, Maria Aleksandra & Logan, Alan, 2016, Recent Brachiopoda from the Mozambique-Madagascar area, western Indian Ocean, Zoosystema 38 (1), pp. 5-41 : 18-22

Eucalathis malgachensis n. sp.

( Fig. 11 ; Table 10)

TYPE MATERIAL. — South Madagascar. ATIMO VATAE, stn CP 3614, holotype ( MNHN IB-2013-64 ; Fig. 11 F-I). — Same locality, stn DW 3552, CP 3614, CP 3615, four paratypes ( MNHN IB-2013- 66 - 69 : Fig. 11 B-E, J-L) .

TYPE LOCALITY. — South Madagascar, South Cap Sainte Marie, ATIMO VATAE, stn CP 3614, 26°14’S, 45°09’E, 250- 300 m.

ETYMOLOGY. — Referring to the Malgache, the French name of the ethnic group that forms nearly the entire population of Madagascar.

DIAGNOSIS. — Eucalathis with fascicostate surface, primary ribs strong, triangular in cross-section, 7 to 9 in number, loop angular at the anterior.

MATERIAL EXAMINED. — South Madagascar. ATIMO VATAE, stn DW 3515, 1 bivalved specimen. — Stn DW 3522, 7 bivalved specimens. — Stn DW 3523, 13 bivalved specimens. — Stn DW 3524, 37 bivalved specimens. — Stn DW 3528, 6 bivalved specimens.— Stn DW 3534, 5 bivalved specimens. — Stn DW 3552, 54 bivalved specimens, 1 ventral valve, 2 dorsal valves. — Stn DW 3553, 76 bivalved specimens, 4 ventral valves, 4 dorsal valves. — Stn DW 3557, 14 bivalved specimens. — Stn DW 3564, 1 bivalved specimen. — Stn CP 3595, 2 bivalved specimens. — Stn DW 3599, 2 bivalved specimens. — Stn CP 3613, 11 bivalved specimens, 1 ventral valve, 1 dorsal valve. — Stn CP 3614, 4 bivalved specimens. — Stn CP 3615, 64 bivalved specimens, 3 ventral valves, 4 dorsal valves.

DEPTH RANGE. — 122- 910 m.

MEASUREMENTS. — See Table 10.

DESCRIPTION

Shell small (maximum length 6.3 mm), strongly biconvex, triangular in outline with greatest width near anterior. Shell surface fascicostate with the dominance of strong, triangular in cross-section, primary ribs 7 to 9 in number; secondary ribs delicate, indistinct. Growth lines distinct. Anterior commissure rectimarginate to incipiently broadly unisulcate. Hinge margin short, straight to slightly curved. Beak suberect to erect with a large, subcircular, mesothyrid foramen; deltidial plates minute, triangular, disjunct. Ventral valve interior with a broad pedicle collar and small, hooked teeth ( Fig. 11E ). Dorsal valve interior with massive inner socket ridges extending beyond margin. Cardinal process prominent ( Fig. 11K, L ). Crura stout, crural processes short. Loop thin, angular at anterior, however, in some specimens it can be thickened ( Fig. 11M ).

REMARKS

This species is the most common brachiopod in the studied material (more than 300 specimens), occurring only in South Madagascar. It differs from hitherto described species of Eucalathis in the strong costation of its broad, triangular in cross-section ribs. A similar triangular ribbed shell is observed in Melvicalathis macroctena , however, ribs in the latter species have smooth ridges without tubercles ( Lee et al. 2008).

Figures

FIG. 11. — Eucalathis malgachensis n. sp., South Madagascar, ATIMO VATAE: A, dorsal view of complete specimen (MNHN IB-2013-65), paratype, South Cap Sainte Marie, stn CP 3614, 250-300 m; B-D, dorsal views of complete specimens and enlargement (D) of umbonal part (MNHN IB-2013-66-67), paratypes, South of Faux-Cap, stn DW3552, 264-280 m; E, inner view of ventral valve (MNHN IB-2013-68), paratype, stn DW 3552; F-I, dorsal, oblique and anterior views of complete specimen, and enlargement (H) of umbonal part, holotype (MNHN IB-2013-64), stn CP 3614; J-L, interior of dorsal valve, and enlargements (K, L) to show details of cardinalia and brachidium, paratype (MNHN IB-2013-69), South Cap Sainte Marie,CP 3615, 284-286 m; M, inner view of dorsal valve (MNHN IB- 2013-70), visible thickened loop, stn DW 3552. All SEMs. Scale bars: A-C, E-G, 2 mm; D, H-J, M, 1 mm; K, 500 µm; L, 200 µm.