Hyattidina remota, Modzalevskaya, 2003

Modzalevskaya, Tatiana L., 2003, Silurian and Devonian brachiopods from Severnaya Zemlya (Russian Arctic), Geodiversitas 25 (1), pp. 73-107 : 100-101

Hyattidina remota n. sp. ( Figs 22 A-D; 30)

HOLOTYPE. — N 58/12991, CNIGR Museum , St. Petersburg ( Fig. 22 A-C), conjoined valves; L = 8.4 mm, W = 8.4 mm, T = 5.6 mm.

ETYMOLOGY. — From remotus (Latin): far.

TYPE LOCALITY. — Loc. 13, Matusevich River, October Revolution Island.

FORMATION. — Golomyannyj Formation.

AGE. — Llandovery, Aeronian.

MATERIAL EXAMINED. — 19 conjoined well preserved valves from loc. 13, bed 48, Matusevich River, October Revolution Island ( Männik et al. 2002: figs 2, 5); Golomyannyj Formation.

MEASUREMENTS (IN MM). — L = 6.8-8.4, W = 7.3-8.4, T = 5.0-5.6.

DIAGNOSIS. — Small shells, rounded in outline, biconvex in lateral profile, plicate; ventral fold and dorsal sulcus are well developed; wide dorsal sulcus limited by the flanking sinuses.

DESCRIPTION

Biconvex shells with rounded outline, plicate. Ventral beak acute, with open delthyrium, curved over the dorsal valve. Rounded ventral sinus limited laterally by rounded plicae, which originate from the anterior half of the valve. Smooth surface covered sometimes anteriorly by concentric growth lines. The internal structures consist of long, low dental plates located fairly close to the valve walls. Teeth small, deeply inserted into the dental sockets ( Fig. 30 ). Crural bases arise from the cardinal plate and progressively curve inward to join the primary lamellae of the spiralia. Spiralia directed laterally comprising five whorls. Jugum simple, placed in the middle of the shell, comprising a pair of joined lamellae without a jugal saddle.

COMPARISON

All hyattidinids possess long, low dental plates, a simple jugum without jugal saddle and spiralia directed laterally. The specimens show some characteristics of Hyattidina junea (Billings, 1866) (such as the pattern of the ventral sinus and dorsal fold), illustrated by Twenhofel (1928: 223, pl. XXX, figs 4-6) from the Gun River and Jupiter formations of Anticosti Island. But the Severnaya Zemlya shells are smaller and characterized by a wider dorsal fold, limited by the flanking sinuses.

Figures

FIG. 22. — A-D, Hyattidina remota n. sp.; A, ventral view; B, dorsal view; C, anterior view of a complete shell (holotype N 58/12991); D, lateral view of a complete shell (N 59/12991), loc. 13, bed 48, Golomyannyj Formation; E-H, Greenfieldia orbiculata n. sp.; E, ventral view; F, dorsal view; G, lateral view; H, anterior view of a complete shell (holotype N 62/12991), loc. 2, bed 66, Samojlovich Formation; I, Meristina? norilica (Nikiforova in Nikiforova & Andreeva, 1961), ventral view of a complete shell (N 61/12991), loc. 13, bed 27, Srednij Formation; J-M, Dubaria tenera Nikiforova & T. Modzalevskaya, 1968; J, ventral view; K, dorsal view; L, lateral view; M, anterior view of a complete shell (N 57/12991), loc. 13, bed 89, Vodopad Formation. Scale bars: A-C, E-H, 5 mm; D, J-M, 3 mm; I, 6 mm.

FIG. 30. — Selected transverse serial sections, illustrating the development of internal structures in Hyattidina remota n. sp. (N 60/12991). Measurements: length 6.8 mm, width 8.4 mm, thickness 5.0 mm; loc. 13, bed 48, Golomyannyj Formation. Numerical designations are the same as on Fig. 11. Scale bar: 5 mm.