Eucalathis daphneae, 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

Eucalathis daphneae n. sp.

( Fig. 10 E-O; Table 9)

TYPE MATERIAL. — North-West Madagascar. MIRIKY, stn DW 3234, holotype ( MNHN IB-2013-61 ; Fig. 10 F-J). — Same data, stn DW 3196, paratypes ( MNHN IB-2013-62 , 63 ; Fig. 10E, K-O) .

TYPE LOCALITY. — Madagascar, MIRIKY, stn DW 3234, 13°27’S, 47°55’E, 187- 247 m.

DIAGNOSIS. — Eucalathis with single, broad, rounded costae nearly smooth in anterior half, and incomplete loop.

MATERIAL EXAMINED. — North-West Madagascar. MIRIKY, stn DW 3196, 8 bivalved specimens. — Stn DW 3234, 2 bivalved specimens, 1 ventral valve, 1 dorsal valve.

DEPTH RANGE. — 187-249 m

DESCRIPTION

Shell small (maximum observed length 5.9 mm), ventribiconvex, widely subtriangular in outline. Shell surface covered with 10-12 strong, single, rounded costae. Costae weakly beaded posteriorly, nearly smooth in anterior half except where crossed by elevated growth lines; intercostal spaces wide. Anterior commissure rectimarginate. Hinge line slightly curved. Beak low, suberect. Foramen large, subcircular, mesothyrid; deltidial plates small, triangular ( Fig. 10E, G). Ventral valve interior with small teeth; pedicle collar wide. Dorsal valve interior with massive inner socket ridges extending beyond margin. Cardinal process distinct. Crura long, slender; crural processes short, can be slightly incurved. Loop short with an incomplete transverse band ( Fig. 10 I-O). Low, short median ridge visible on inner dorsal valve. Inner margin of both valves crenulated.

REMARKS

In size, outline and ornamentation the new species described here is most similar to Eucalathis rotundata . In the strong costation E. daphneae n. sp. also resembles E. rugosa Cooper, 1973 , differing in size and outline, as well as in the character of costae. E. rugosa possesses beaded, strongly tuberculate ribs ( Cooper 1973c; Laurin 1997; Bitner 2008, 2009, 2010); in E. daphneae ribs are nearly smooth. However, the species described by Cooper (1973c, 1981a) have a typical loop for the genus, whereas in all specimens collected in North-West Madagascar the loop has an incomplete transverse band.

Among Recent representatives of chlidonophorids only in the species Melvicalathis macroctena (Zezina, 1981) may the loop be incomplete ( Zezina 1981b; Lee et al. 2008), however, it possesses broad, triangular in cross-section costae with smooth ridges without any tubercles, differing greatly from E. daphneae . In the fossil chlidonophorids an incomplete loop is observed only in the Eocene-Oligocene genus Orthothyris Cooper, 1955 (see Bitner & Müller 2015).