Semitreta maior Biernat, 1973
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publication ID |
https://doi.org/ 10.13140/rg.2.1.3543.9120 |
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persistent identifier |
https://treatment.plazi.org/id/FB5C1130-FFB1-593A-FFFE-D2FC0E0EFC64 |
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treatment provided by |
Felipe |
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scientific name |
Semitreta maior Biernat, 1973 |
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Semitreta maior Biernat, 1973 View in CoL
Fig. 8 View Fig .
Semitreta maior sp. n.; Biernat 1973: 76, pl. 10: 1–11, fig. 27. Semitreta maior Biernat ; Holmer and Popov 2000: 119, fig. 61, 3a–f. Holotype: Bp. XV/11u, ventral valve (W = 1.1, L = 1.3)
Type locality: Wysoczki. Holy Cross Mountains , Poland .
Type horizon: Tremadoc chalcedonites.
Material.—Total of 50 dorsal and 72 ventral valves. Figured ventral valves: RM Br133809 (W = 2.23, L = 2.10, H = 2.62), RM Br133811 (W = 0.39, L = 0.37, H = 0.37), RM Br133816 (W = 0.71, L = 0.60, H = 0.77); dorsal valves RM Br133807 (W = 1.27, L = 1.07), RM Br133808 (W = 0.95, L = 0.80, WI = 0.38, LI = 0.10, LS = 0.55), RM Br133810, RM Br133812, RM Br133813, RM Br133814, RM Br133815 (W = 1.52, L = 1.28, WI = 0.67, LI = 0.10).
Diagnosis.—Ventral valve high, narrowly conical, more than 100% as high as long. Ventral pseudointerarea poorly defined, apsacline. Foramen on short exterior pedicle tube. Ventral apical process elongate triangular, anterior to internal foramen. Dorsal valve flattened to geniculate, with weak median sulcus. Dorsal pseudointerarea strongly raised with triangular median groove and strongly anacline propareas. Dorsal cardinal muscle fields poorly impressed. Dorsal median buttress and median ridge variably developed.
Description.—Shell transversely suboval, around 80–95% as long as wide (N = 6). Ventral valve high, around 100–140% as high as long (N = 3). Foramen apical around 30–40 µm across, on short exterior tube, enclosed within larval shell. Ventral pseudointerarea poorly defined, apsacline. Ventral apical process elongate triangular, extending for about 30% of distance from apex to anterior margin (N = 1). Dorsal valve flattened to geniculate in lateral view, with weak median sulcus starting at umbo. Dorsal pseudointerarea strongly raised, occupying less than half of valve width, with triangular median groove and strongly anacline propareas. Dorsal cardinal muscle fields poorly impressed. Dorsal median buttress and median ridge variably developed; low and broad median septum commonly present, starting directly anterior to median buttress and extending anterior to mid−length.
Larval shell of both valves circular, about 0.15–0.20 mm across.
Discussion.—This species is the most common in the brachiopod fauna from the chalcedonites. Holmer and Popov (2000) and Popov and Holmer (1994) most recently discussed the affinities of Semitreta . In addition, Semitreta kotujensis Ushatinskaya (1994) from the Cambrian of Siberia has been described. The ventral valve of S. kotujensis is poorly known, but it would appear that the type species differs from all other taxa in having a narrow, high conical ventral valve with a foramen on a short exterior tube, a poorly developed apical process, in addition to a geniculate somewhat sulcate dorsal valve. The geniculation is particularly strong in gerontic specimens. By comparison with the material described by Biernat (1973), the dorsal cardinal muscle fields are more poorly impressed, and the dorsal median buttress and median ridge more variably developed.
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