Paromalomena polonica ( Temple, 1965 )

Hints, Linda & Harper, David A. T., 2015, The Hirnantian (Late Ordovician) brachiopod fauna of the East Baltic: Taxonomy of the key species, Acta Palaeontologica Polonica 60 (2), pp. 395-420 : 399-400

Paromalomena polonica ( Temple, 1965)

Fig. 4A, B, F–H .

1965 Platymena? polonica n. sp.; Temple 1965: 407–410, pl. 15: 1–4; pl. 16: 1–5.

2008 Paromalomena polonica (Temple) ; Cocks 2008: 63 (see synonyms therein).

Material.— Eight specimens embedded in rock. Porkuni Regional Stage , Kuldiga Formation , Hirnantian ( Upper Ordovician ); Latvia, Estonia. Drill core and depth (in meters) of sample with brachiopod. Depth of fragmentary specimens is marked by “?”. Collection GIT 542 : Aispute-41, 1000.5; Ikla, 535.3; Mežmaļi-16, 911.8–912.5; Ruhnu-500, 616.2

the lowermost scabra chitinozoan zone; Nõlvak 2003), 617.4; Vilcini-15,?914.5; collection LDM G: Pliekalni-14,

884.0–884.6.

Remarks.—Small semicircular shells up to 15 mm wide and 10.5 mm long with multicostellate ornament of fine and uniform costellae; the irregular growth lines, partly developed as low rugae, are most similar to those on the Polish specimens of P. polonica ( Temple 1965: pl. 15: 2, 3). The Baltic specimens have obtuse to acute cardinal angles, hinge line 0.9 of valve width. Costellae appear at 2 to 3 mm growth stage; up to 9 costellae per 1 mm at 5 mm from apex, few costellae appear along the posterior margin. Ventral valve very weakly convex around the umbo; dorsal valve flat, anteriorly slightly concave with a low, anacline dorsal interarea with grooved chilidium ( Fig. 4H 1).

The Baltic specimens differ somewhat from the Polish specimens in shell outline, the ratios of width to length are about 1.4 and 1.6, respectively ( Temple 1965).

The Baltic as well the Polish specimens differ from those from China ( Rong 1984; Zhan et al. 2010) in having somewhat larger shells. The early growth stages, up to 3.5 mm generally lack radial ornament, similar to some specimens of the genus Proboscisambon .

Stratigraphic and geographic range.—This widespread species is mainly restricted to the Hirnantian Stage, Upper Ordovician, although similar forms occur in both the highest Katian and lowest Llandovery. It is common in deeper-water facies in Argentina, Burma, China, Thailand, and parts of Europe, for example, Austria, the Czech Republic, Poland, and England (see, e.g., Benedetto 1990; Rong and Harper 1988; Rong et al. 2002; Temple 1965). In Baltoscandia, it occurs in Sweden ( Bergström 1968), Estonia, and Latvia this paper).

Figures

Fig. 4. Strophomenoid brachiopods from the Kuldiga Formation of the Porkuni Regional Stage, Hirnantian (Upper Ordovician), East Baltic, western Latvia (A–F, H) and southwestern Estonia (G). A, B, F–H. Paromalomena polonica (Temple, 1965). A. Dorsal valve, GIT 542-299, Mežmali-16, depth 911.8 m, exterior view. B. Dorsal valve, GIT 542-352-1, Adze-6, 844.5 m, split into two parts: exterior view (B1) and impression (B2). F. Dorsal valve, GIT 542-377, Aispute-41, 884.4 m, exterior view.G. Dorsal valve, GIT 542-361, Ikla, 535.3 m, exterior view. H. Dorsal valve, GIT 542-355, Mežmali-16, 912.2 m, exterior view (H 1) and view of the chilidium (H2). C. Eostropheodonta cf. parvicostellata Rong, 1984. Dorsal valve, GIT 542-365, Aispute-41, depth 988.7 m, exterior view. D–E. Proboscisambon? sp. D. Mould of dorsal valve, GIT 542-53, Stirnas-18, depth 908.2 m, exterior view. E. Dorsal valve, GIT 542-322-1, exterior view; Riekstini-15, 858.6 m. Scale bars 2 mm.