Crurithyris cf. nastus Brunton and Champion, 1974

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 : 823-824

Crurithyris cf. nastus Brunton and Champion, 1974

Figs. 4G, H , 23 .

Material.—About a hundred shells and more than 500 single valves from samples D1, D2, GB, GT, MH1, and MH2−8.

Description.—Shell small, strongly ventribiconvex, rectangular to sub−circular in outline, usually wider than long, with hinge line about two−third of the shell width; lateral margins rounded, anterior margin slightly emarginate. Ventral valve deep, posteriorly inflated; interarea apsacline and concave; shallow median sulcus appears near the umbo. Dorsal valve transversely elliptical in outline with very short interarea; sulcus present but very weak to imperceptible.

Inner socket ridges, crural bases, crura and cardinal process are figured on well preserved dorsal valve in Figure 23C, D (see also Fig. 23I ). Sockets diverge from hinge line at about 23–25 °. Inside the ventral valve there is a low median ridge extending about one−half of the valve length ( Fig. 23B 1 , G).

Although the majority of the specimens from Muhua display smooth shell surfaces ( Fig. 23A ) well preserved specimens show a spinose micro−ornamentation. On the ventral valve here figured ( Fig. 23F ) two sizes of micro−spines are well seen, similar to the condition observed by, e.g., George (1931) in Crurithyris magnispina and by Brunton (1984) in Crurithyris urei .

Remarks.—This species is the most numerous in the fauna of the Muhua Formation. It is especially dominant in the sample MH1 which is characterised by the highest taxonomic diversity of all samples studied from this area.

The specimens show great similarity to Crurithyris nastus described from the Early Carboniferous (Viséan) of Staffordshire, British Isles (see Brunton and Champion 1974: 830 –

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

833, pl. 110: 6–16; text−fig. 6). The former shows some external resemblance to Crurithyris parvus Xu and Yao, 1988 described from the Tournaisian of Nanbiancun section, Guilin Province, China ( Xu and Yao 1988: 287, pl. 72: 6–9) but differs in having wider shell and higher ventral interarea.

Stratigraphic and geographic range.— C. nastus was described from rocks of probably early Viséan age (Chadian) of the Manifold valley, Staffordshire. The very similar specimens described herein are from Tournaisian of Muhua, southern China.

Figures

Fig. 4. Shell damage in silicified brachiopods from the Tournaisian Muhua Formation, southern China. A. Drilled ventral valve of Subglobosochonetes gedongguensis Sun and Baliński, 2008, PKUM02−0390, in exterior (A1) and interior (A2) views. B, C. Two shells of Cleiothyridina deroissyi (Léveillé, 1835) with boreholes, PKUM02−0391 (B) and PKUM02−0392 (C), in dorso−lateral (B) and ventral (C) views, respectively. D, E. Two damaged shells of Cleiothyridina tenuilineata (Rowley, 1900) with boreholes, PKUM02−0393 (D) and PKUM02−0394 (E), in dorsal (D1, E1) and enlarged (D2, E2) views. F. Damaged ventral valve of Cleiothyridina tenuilineata (Rowley, 1900), PKUM02−0395, in general exterior (F1) and more detailed (F2) views. G, H. Two shells of Crurithyris cf. nastus Brunton and Champion, 1974 with boreholes, PKUM02−0396 (G) and PKUM02−0397 (H), in general dorsal (G1, H1) and detailed (G2, H2) views. I. Shell of Cleiothyridina deroissyi (Léveillé, 1835), PKUM02−0398, with a few small−sized boreholes in dorsal valve. J. Shell of Cleiothyridina tenuilineata (Rowley, 1900) with a series of small−sized boreholes, PKUM02−0399, in ventral (J1) and enlarged (J2) views. K, L. Two dorsal valves of Cesifornix carteri Baliński and Sun, 2010a, PKUM02−0400 (K) and PKUM02−0401 (L), bored from the exterior (K1, L1) and showing “blister” deposits in the interior (K2, L2) as a response to borings. M. Dorsal valve of Schellwienella sp., PKUM02−0317, showing numerous external borings of a barnacle (M1) and internal “blisters” sealing the damages (M2) (illustrated by Baliński and Sun 2008: fig. 21D; M2 new photograph). N. Koskinoid perforations in posterior region of ventral valve of Serratocrista sp., PKUM02−0402. Samples GB/GT (A, N), MH1 (B–G, I–L), and MH2 (H, M).

Fig. 23. Ambocoeliid brachiopod Crurithyris cf. nastus Brunton and Champion, 1974 from the Tornaisian Muhua Formation, southern China. A. Complete shell PKUM02−0496 in dorsal (A1), ventral (A2), lateral (A3), and posterior (A4) views. B. Small ventral valve, PKUM02−0497, in interior (B1), lateral (B2), and posterior (B3) views. C, D. Interior of two dorsal valves (C, D1) and enlarged view of cardinalia (D2), PKUM02−0498 (C) and PKUM02−0499 (D). E. Interior of very small ventral valve, PKUM02−0500. F. Anterior view of ventral valve, PKUM02−0501, exterior showing spinose micro−ornamentation. G. Interior of ventral valve (G1) and enlargement of the umbonal region (G2), PKUM02−0502. H. Enlargement of the interior of dorsal valve, PKUM02−0503, showing cardinalia and muscle scars. I. Stereomicrographs of shell, PKUM02−0504, in dorsal view with much of the dorsal valve removed showing crura and the beginning of the spiralium; another small dorsal valve is seen deep behind crura. A–G, I, SEM micrographs. All from sample MH1.

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).