Megerella hilleri, 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 : 32-35

Megerella hilleri n. sp.

( Figs 18 , 19 ; Table 17)

TYPE MATERIAL. — South Madagascar. ATIMO VATAE, stn DW 3519, holotype ( MNHN IB-2013-508 ; Fig. 18 G-I). — Same locality,stn DW 3519, DW 3532, DW 3534, 5 paratypes ( MNHN IB- 2013-509 , 511 , 513-515 ; Figs 18 D-E; 19C-E, G-M) .

TYPE LOCALITY. — South Madagascar, between Lokaro and Ste Luce, 24°52’S, 47°28’E, stn DW 3519, 80- 83 m.

ETYMOLOGY. — Named in honour of Norton Hiller (Melbourne, Australia) in recognition of his work on brachiopods from the Indian Ocean .

DIAGNOSIS. — As for the genus.

MATERIAL EXAMINED. — South Madagascar. ATIMO VATAE, stn DW 3515, 1 bivalved specimen. — Stn DW 3518, 1 bivalved specimen. — Stn DW 3519, 19 bivalved specimens, 1 ventral

valve, 1 dorsal valve. — Stn CP 3520, 2 bivalved specimens. — Stn DW 3522, 2 bivalved specimens. — Stn DW 3530, 14 bivalved specimens. — Stn DW 3531, 3 bivalved specimens. — Stn DW 3532, 9 bivalved specimens. — Stn DW 3534, 6 bivalved specimens, 1 ventral valve, 1 dorsal valve. — Stn DW 3564, 1 bivalved specimen. — Stn CP 3573, 1 bivalved specimen. — Stn CP 3614, 1 bivalved specimen.

DEPTH RANGE. — 54- 456 m.

MEASUREMENTS. — See Table 17.

DESCRIPTION

Shell small (maximum observed length 4.4 mm), subquadrate in outline, usually wider than long, maximum width at mid-line, biconvex with slightly more convex ventral valve. Shell surface costate with 15-25 radiating ribs, widely spaced and rounded in profile on dorsal valve and weakly beaded on ventral valve; ribs never bifurcate but rare intercalating ribs are observed. Lateral commissures straight, anterior commissure rectimarginate to incipiently sulcate in some larger specimens. Hinge line long, straight. Beak short, suberect, usually abraded due to very short pedicle ( Fig. 18A ). Beak ridges sharp. Cardinal area in ventral valve striated. Foramen large, deltidial plates narrow, disjunct.

Ventral valve interior with short but well-developed pedicle collar.Teeth small, hooked, supported in adults by weak dental plates ( Fig. 19 A-E). Median septum not present in early stages ( Fig. 19 A-B) but extending about ⅔ length of valve in adult forms ( Fig. 19 C-E). Margin of valve with single row of tubercles in adult form, each tubercle tip excavated. Dorsal valve interior with no cardinal process; divergent inner socket ridges excavate below, outer hinge plates broad, dental sockets relatively deep. Short rudimentary crura attached to inner sides of socket ridges ( Fig. 19 F-M). Centrally-placed septal pillar bearing bifurcate loop of brachial skeleton with distal extensions uniting to form a complete oval ring ( Fig. 19 G-M), lateral extremities of ring with slight claw-like development ( Fig. 19 J-M). Interiors of both valves endopunctate, but with size and disposition of punctae variable, radial ridges weakly developed, terminating in a single peripheral row of prominent tubercles, some with excavated tips ( Fig. 19K ), along inner margin of commissure ( Fig. 19 G-I, K, L). Lophophore plectolophous, mantle spiculate.

REMARKS

The ribbed ornamentation, large foramen, no development of crura and descending branches, and brachial skeleton in the form of an oval structure arising from the centre of the dorsal valve indicate the attribution of the studied specimens to the family Kraussinidae and subfamily Kraussininae (see Hiller et al. 2008). They differ, however, greatly from other members of this subfamily, Kraussina Davidson in Suess, 1859, Megerlina Eudes-Deslongchamps, 1884 , and Pumilus Atkins, 1958 , in which brachial lamellae are not united and form a V-shaped structure.

Figures

FIG. 18. — Megerella hilleri n. gen., n. sp. South Madagascar, ATIMO VATAE:A, complete specimen (MNHN IB-2013-100) in living position attached to bryozoan, between Lokaro and Ste Luce, stn DW 3519, 80-83 m; B, dorsal view of immature complete specimen (MNHN IB-2013-506), stn DW 3519, 80-83 m; C, dorsal view of complete specimen (MNHN IB-2013-507), sector of Sainte Luce, stn DW 3534, 296-307 m; D-F, ventral and dorsal views of complete specimen, and enlargement (F) of umbonal part to show details of beak and area, paratype (MNHN IB-2013-509), north of Sainte Luce, stn DW 3532, 86-87 m; G-I, ventral and dorsal views of complete specimen, and enlargement (I) of umbonal part, holotype (MNHN IB-2013-508), stn DW 3519, 80-83 m. All SEMs.Scale bars: A, 2 mm; B, F, I, 500 µm; C-E, G, H, 1 mm.

FIG. 19. — Megerella hilleri n. gen., n. sp., South Madagascar, ATIMO VATAE: A, B, young individual (MNHN IB-2013-510), inner view of ventral valve and enlargement of umbonal part to show details of teeth,between Lokaro and Ste Luce,stn DW 3519,80-83 m; C, inner view of ventral valve paratype (MNHN IB-2013-511), stn. DW 3519, 80-83 m; D, E, inner and oblique views of ventral valve, and enlargement (E) of umbonal part to show details of pedicle collar and median septum, paratype (MNHN IB-2013-512), sector of Sainte Luce, stn DW 3534, 296-307 m; F, inner view of dorsal valve of young individual (MNHN IB-2013-513), stn DW 3519; G-J, dorsal valve, inner, oblique and posterior views, and enlargement of tilted anterior view, to show details of cardinalia and brachial skeleton, paratype (MNHN IB-2013-514), stn DW 3534; K-M, inner and posterior views of dorsal valve, and enlargement of anterior tilted view, paratype (MNHN IB-2013-515), stn DW 3519. All SEMs. Scale bars: A, B, F, 200 µm; C, D, G-I, K, L, 1 mm; E, J, M, 500 µm.