Palaeochoristites cinctus ( Keyserling, 1846 ) Eochoristites Chu, 1933

Sun, Yuanlin & Baliński, Andrzej, 2011, Silicified Mississippian brachiopods from Muhua, southern China: Rhynchonellides, athyridides, spiriferides, spiriferinides, and terebratulides, Acta Palaeontologica Polonica 56 (4), pp. 793-842 : 818-823

Palaeochoristites cinctus ( Keyserling, 1846)

Fig. 20 .

1846 Spirifer cinctus Keyserling ; Keyserling 1846: 229, pl. 8: 2.

1941 Palaeochoristites cinctus (Keyserling) ; Sokolskaya 1941: 29–34, pl. 3: 1–5; pl. 10: 1–3.

1952 Palaeochoristites cinctus (Keyserling) ; Sarytcheva and Sokolskaya 1952: pl. 55: 321.

1979 Palaeochoristites cf. cinctus ( Keyserling, 1846) ; Nalivkin 1979: 139, pl. 54: 1, 2; pl. 55: 1.

2002 Palaeochoristites cinctus ( Keyserling, 1846) ; Sartenaer and Plodowski 2002: pl. 4: 26–30.

Material.—One complete juvenile shell ( Fig. 20A ; dimensions in mm: length 9.5, width 14.4, thickness 6.0), 3 complete dorsal and one complete ventral valves, and 35 fragments of single dorsal and ventral valves. All from sample

MH 1. Description.—Medium sized, elliptical transverse in outline,

ventribiconvex; cardinal margin straight but much shorter than the maximum shell width which is located slightly anterior to the hinge line; cardinal extremities well rounded, anterior commissure rectimarginate.

Ventral valve with triangular, concave, but relatively low interarea; delthyrium open; median sulcus almost not distinguishable, but on one juvenile shell a pair of thicker costae suggest the presence of a sulcus ( Fig. 20A 2).

Dorsal valve less convex than the ventral one, with well marked umbonal swelling; interarea very low but subtriangular, sockets very narrow, anteriorly diverging at 101–113 °; fold not developed, although on one specimen a pair of better marked intercostal, fold bounding spaces can be observed.

Interior of ventral valve with vertically subparallel dental plates. Dorsal valve with very small cardinal process and wide subvertical inner socket ridges which together with crural bases form sub−rectangular, almost flat plates fused with the valve floor only posteriorly, thus forming variably developed crural plates ( Fig. 20C–E ); anteroventral margin of inner socket ridges high, extending above the plane marked by the surface of the dorsal interarea. On one of the dorsal valves two pairs of adductor scars can be recognised ( Fig. 20E ): short and wide posterior pair and elongate, longitudinally striated anterior one; the scars divided medianly by wide longitudinal ridge.

External surface multicostate, costae rounded to subangular, frequently bifurcate, rarely trifurcate.

Remarks.—This species is represented in the material by one juvenile shell and scanty single valves only. Nevertheless, characteristic shape and external ornamentation are highly indicative of these valves representing a species of the genus Palaeochoristites . The valves are transversely elliptical in outline with rounded cardinal extremities and either lack a fold and sulcus or these are weakly developed. Crural bases form sub−rectangular, almost flat plates fused with the valve floor only posteriorly, thus forming variably developed crural plates.

http://dx.doi.org/10.4202/app.2010.0106

The specimens are identical with Palaeochoristites cinctus described from the Tournaisian of the European Russia and the Urals ( Sokolskaya 1941; Sarytcheva and Sokolskaya 1952; Nalivkin 1979). A single specimen described as Palaeochoristites cinctus from Kunlun Mountains ( China) by Chen and Shi (2003: 164, pl. 10: 21–25) most probably does not represent the species nor the genus because it possesses well marked dorsal fold and ventral sulcus. The type material of Palaeochoristites mediatus Liao, 2006 described from the early Carboniferous of Jinbo, Hainan Island, China ( Liao and Zhang 2006), is so fragmentary that no reliable comparison can be made. Also, shell costation in our specimens is much thinner.

Figures

Fig. 20. Palaeochoristitid brachiopod Palaeochoristites cinctus (Keyserling, 1846) from the Tornaisian Muhua Formation, southern China. A. Complete young shell, PKUM02−0477, in dorsal (A1), ventral (A2), lateral (A3), posterior (A4), and anterior (A5) views. B. Ventral valve, PKUM02−0478, viewed from the exterior (B1), interior (B2), and posterior (B3). C. Dorsal valve, PKUM02−0479, in exterior (C1) and interior (C2) views. D. Dorsal valve, PKUM02−0480, in exterior (D1), interior (D2), and the same inclined anteriorly (D3) views. E. Interior of incomplete dorsal valve, PKUM02−0481, in general (E1), and enlarged (E2) views showing cardinalia with crural plates. F. Ventral valve, PKUM02−0482, in exterior (F1) and interior (F2) views. G. Detail of external ornamentation, dorsal valve, PKUM02−0483. All from sample MH1.

Fig. 6. Shell damage and malformation in silicified brachiopods from the Tornaisian Muhua Formation, southern China. A. Incomplete dorsal valve of orthotetide Schuchertella sp., PKUM02−0320, in general external (A1) and more detailed (A2) views showing damage to the middle anterior margin at the earlier stage of growth resulting in bilobate outline of the valve; note also disturbance of median costellae and a later recovery after some arrest of growth (specimen illustrated also by Sun and Baliński 2008: fig. 22C). B, C. Two dorsal valves of orthotetide Lamellispina spinosa Sun and Baliński, 2008, PKUM02−0406 and PKUM02−0407, viewed from the interior showing distortion/malformation of growth due to crowding. D. Seriously damaged ventral valve of spiriferide Celsifornix carteri Baliński and Sun, 2010a, PKUM02−0408, in external (D1) and internal (D2) views showing full recovery after some arrest of growth; note another (subsequent) repaired damage on the left flank of the specimen. E. Incomplete ventral valve of spiriferide Parallelora sp., PKUM02−0409, in external (E1) and enlarged (E2) views showing repaired damage. F. Incomplete ventral valve of spiriferide Celsifornix carteri Baliński and Sun, 2010a, PKUM02−0410, in external (F1) and internal (F2) views showing broken off and repaired the lateral part of the right flank. G. Ventral valve of spiriferide Eochoristites neipentaiensis Chu, 1933, PKUM02−0411, in oblique lateral view showing repaired damage of the right lateral extremity. H. Dorsal valve of spiriferide Eochoristites neipentaiensis, PKUM02−0412, in external (H1) and internal (H2) views with scalloped anterolateral margin of the left flank showing full repair of the damage. Samples MH1 (A–D, F), MH2 (G, H), and GB (E). Scale bars 2 mm.

Fig. 22. Palaeochoristitid Eochoristites neipentaiensis Chu, 1933 from the Tornaisian Muhua Formation, southern China. SEM stereopair of incomplete dorsal valve, ZPAL V.XXVI/70, showing development of short dorsal adminicula. Sample D3.

Fig. 1. Stratigraphic columns (A) and map (B) of the sampling sites around Muhua and Gedongguan villages in Guizhou Province, southern China (after Sun and Baliński 2008).