Anabaria, Lopushinskaya, 1965

Modzalevskaya, Tatiana L., 2003, Silurian and Devonian brachiopods from Severnaya Zemlya (Russian Arctic), Geodiversitas 25 (1), pp. 73-107 : 90-92

Anabaria ? latens n. sp. ( Figs 14 F-I, Q, T-V; 20)

HOLOTYPE. — N 50/12991, CNIGR Museum , St. Petersburg ( Fig. 14 F-I), conjoined valves; L = 9.2 mm, W = 10.0 mm, T = 7.5 mm.

ETYMOLOGY. — From latens (Latin): hidden.

TYPE LOCALITY. — Loc. 11, Matusevich River, October Revolution Island.

FORMATION. — Samojlovich Formation.

AGE. —?Llandovery,?Telychian.

MATERIAL EXAMINED. — 19 discrete specimens (and specimens embedded in rock) from loc. 13, beds 27, 30-31, 64 and 89, and one specimen (and some fragments) from loc. 11, bed 6B, Matusevich River, October Revolution Island ( Männik et al. 2002: figs 2, 5); Vodopad, Golomyannyj, Srednij and Samojlovich formations.

MEASUREMENTS (IN MM). — L = 8.2-9.2, W = 8.7- 11.0, T = 3.7-7.5 mm.

DIAGNOSIS. — Shells of small size, almost biconvex in lateral profile; isometrical or subpentagonal in outline, with coarse costae; ventral sinus wide and flat.

DESCRIPTION

Shells small, pentagonal in outline, unequally biconvex, isometrical or with the width slightly larger than the length. Ventral beak high, incurved, with delthyrium, closed by deltidial plates posteriorly. Ventral sinus flat and wide. Dorsal fold not high, fluently merging in lateral flanks of the valve. Anterior margin uniplicate. Rounded, low costae gradually widened anteriorly and increased by intercalation from 24 to 40 with concentric growth lines. Interior of ventral valve with long, thin dental plates, placed closely to the shell walls; teeth small. Discrete horizontal cardinal plate supports vertically flattened crura. Myophragm extends on two thirds of the valve length. Spiralia are not found ( Fig. 20 ).

COMPARISON AND REMARKS

Anabaria ? latens n. sp. resembles small ribbed atrypids and rhynchonellids. That is why the lack of spiralia makes difficult to attribute these brachiopods to any genus exactly. The almost isometrical biconvex shells with rounded ribs and shallow ventral sinus found in the studied material allow to assign them to genus Anabaria ? The specimens from Srednij Formation possess dorsally curved anterior margin and fine ribs which make them similar to Anabaria rara ( Nikiforova, 1961) from the Talikit and Omnutakh formations of East Siberia ( Nikiforova & Andreeva 1961: 248, pl. LIV, figs 1-7). The differences include rounded pentagonal outline, more acute apical angle, and coarser ribs on Anabaria ? latens n. sp. than on Anabaria rara .

The new species is indistinguishable in the pattern of ribs, and number of ribs in the ventral sinus, from Lenatoechia elegans ( Nikiforova, 1961) from the Omnutakh Formation of East Siberia ( Nikiforova & Andreeva 1961: 205, pl. XLIV, figs 1-7). Despite their small size, the specimens from the Golomyannyj Formation are characterized by isometrical outline and well defined flat ventral sinus. They are also similar to Pseudocamarotoechia ? gljadensis Kul’kov, 1974 from the Gora Gljaden’ Formation (Ivanovsky & Kul’kov 1974: 55, pl. XIX, figs 11, 12) but differ in having well developed dental plates and undeveloped dorsal septum.

Figures

FIG. 14. — A-E, Stegerhynchus? decemplicatus duplex Nikiforova & T. Modzalevskaya, 1968; A, ventral view; B, dorsal view; C, lateral view; D, anterior view; E, enlarged external surface of a complete shell (N 38/12991), loc. 13, bed 89, Vodopad Formation; F-I, V, Anabaria? latens n. sp.; F, dorsal view; G, ventral view; H, lateral view; I, anterior view of a complete shell (holotype N 50/12991), loc. 11, bed 6B, Samojlovich Formation; V, enlarged external surface of a poorly silicified shell (N 51/12991), loc. 29a,?Vodopad Formation; J-P, R, S, Lenatoechia octjabrensis n. sp.; J, ventral view; K, dorsal view; L, lateral view; M, anterior views of a complete shell (N 41/12991), loc. 11, bed 6B, Samojlovich Formation; N, ventral view; O, dorsal view; P, lateral view of a complete shell (holotype N 40/12991), loc. 2, bed 66, Samojlovich Formation; R, ventral view; S, dorsal view of complete shell (N 42/12991), loc. 117v,?Samojlovich Formation; Q, T, U, Anabaria? latens n. sp.; Q, pedicle valve of a complete shell (N 52/12991), loc. 13, bed 27, Srednij Formation; T, ventral view; U, dorsal view of a complete shell (N 53/12991), loc. 13, bed 64, Golomyannyj Formation. Scale bars: A-D, F-M, 5 mm; E, V, 2 mm; N-U, 3 mm.

FIG. 20. — Selected transverse serial sections, illustrating the development of internal strutures in Anabaria? latens n. sp. (N 54/12991). Measurements: length 8.7 mm, width 8.7 mm, thickness 6.2 mm; loc. 13, bed 64, Golomyannyj Formation. Numerical designations are the same as on Fig. 11. Scale bar: 3.2 mm.