Monitilora Iredale, 1930

Taylor, John D. & Glover, Emily A., 2018, Hanging on - lucinid bivalve survivors from the Paleocene and Eocene in the western Indian Ocean (Bivalvia: Lucinidae), Zoosystema 40 (7), pp. 123-142 : 136

Genus Monitilora Iredale, 1930

Monitilora Iredale, 1930: 390 .

TYPE SPECIES. — Lucina ramsayi Smith, 1885 (original designation).

DIAGNOSIS. — Shell white, subcircular, H to 25.0 mm, moderately inflated, light-shelled. Sculpture of fine, rounded, closely spaced, commarginal lamellae with fine radial riblets in the interspaces. Lunule, sunken, asymmetric with greater part in left valve. Hinge plate narrow, right valve with a single small cardinal tooth, small anterior lateral tooth; left valve with two small cardinal teeth and no lateral teeth. Anterior adductor scar medium length, ventrally detached for ½ of length, dorsal part much broader than ventral extension. Pallial line entire, shell margin smooth.

INCLUDED SPECIES. — M. ramsayi ( Smith, 1885) , M. subtilis Glover & Taylor, 2016 , M. sepes ( Barnard, 1964) , M. bonneti ( Cossmann, 1923) .

GEOLOGICAL RANGE. —?Early Cretaceous, Paleocene to Recent.

REMARKS

Originally described from eastern Australia ( M. ramsayi ), species are now known from the Philippines ( M. subtilis ) and a poorly documented species from southern India, originally described from Pliocene deposits ( M. bonneti ), as well as M. sepes from the southwestern Indian Ocean. An undescribed species is present in collections (NHMUK) from western Thailand. It should be noted that, excepting M. ramsayi , various Australian species that have been placed in Monitilora (e.g. Lamprell & Whitehead 1992) belong in other genera.

Shells with characters very similar to the living Monitilora ramsayi and other species can be recognised from the early Paleocene. For example, Monitilora duponti (Cossmann, 1908) from the Calcaire de Mons, Belgium (Danian) ( Fig. 8A, B ) was previously classified in the genus by Chavan (1937 - 1938), and also Monitilora concinna ( Deshayes 1857) from the Thanetian of the Paris Basin. Recorded from the Eocene of the Paris Basin (Lutetian-Bartonian) are Monitilora elegans (Defrance, 1824) and Monitilora baudoni ( Deshayes, 1857) ( Fig. 8C, D ). The post-Eocene fossil record of Monitilora is scant and poorly documented; species are known from Miocene (Badenian) of Poland ( Studencka 1986), Japan ( Itoigawa 1957), Pliocene of India ( Cossmann 1923) and Pliocene of South Australia ( Ludbrook 1955).

Molecular analysis ( Taylor et al. 2011) suggests that Monitilorinae split from other lucinids at least by the mid-Cretaceous. Some Monitilora -like bivalves were present in the Mesozoic but have been placed in Mesomiltha or Myrtea . Examples are Mesomiltha cf fallax, from the Cretaceous (Cenomanian) of India ( Kendrick & Vartak 2007, figs 13I-M) and Myrtea ? monobeana Tashiro & Kozai (1988: 36, pl. 2 figs 29-32, text Fig. 2 ) from the early Cretaceous of Japan.

Figures

FIG. 8. — Monitilora Iredale,1930, Palaeogene fossils (A-D) and Monitilora sepes (Barnard,1964) Inhaca,Mozambique (E-Q): A, B, Monitilora duponti (Cossmann, 1908) Paleocene, Danian, Calcaire de Mons, Mons Puits Coppée, Belgium (RBINS I.G. 6544), L 17.5 mm; C, D, Monitilora obliqua baudoni (Deshayes, 1857) Eocene, Lutetian, Amblainville, Oise, France, Chavan collection (RBINS I.G. 21.735), L 18 mm; E, F, Monililora sepes exterior and interior of left valve, Inhaca stn MD11, L 15 mm; G, H, exterior and interior of right valve, Inhaca stn MD15, L 12.1 mm; I, J, exterior and interior of right valve, Inhaca stn MD15, L 10.2 mm; K, L, exterior and interior of right valve, Inhaca stn MD15, L 10.1 mm; M, interior of left valve, Inhaca stn MD15, L 8.4 mm; N, O, detail of hinge teeth of left and right valves of H, I; P, detail of external sculpture of K; Q, protoconch of H. Scale bars: N, O, 1.0 mm; P, 500 µm; Q, 100 µm.

FIG. 2. — Gibbolucina zelee n. sp., Banc de la Zélée, Mozambique Channel, BENTHEDI stn R110, 24 m: A-D, holotype (MNHN-IM-2000-33710) exterior and interior of left and right valves, L 15.3 mm; E, F, paratype (MNHN-IM-2000-33711) exterior and interior of left valve, L 12.7 mm; G, paratype (as E, F) interior of right valve with reconstituted body, L 12.7 mm; H-J, paratype (MNHN-IM-2000-33711) exterior of right valve and interior of right and left valves, L 17.7 mm; K, L, paratype (MNHN-IM-2000-33711) exterior of right valve and dorsal view,L 10.5 mm; M, N, paratype (MNHN-IM-2000-33711) exterior of left valve and dorsal view, L 9.2 mm; O, P, paratype (MNHN-IM-2000-33711) interior of right and left valves, L 8.9 mm; Q, R, paratype (MNHN-IM-2000-33711) detail of hinge teeth of right and left valves of O & P; S, protoconch of Q. Abbreviations: am, anterior adductor muscle;f, foot; ld, left demibranch; pa, posterior apertures; pm, posterior adductor muscle. Scale bars: Q, R, 1.0 mm; S, 100 µm.