Muhuathyris circularis Sun, Ma, Baliński, and Zhang, 2004

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 : 817

Muhuathyris circularis Sun, Ma, Baliński, and Zhang, 2004

Fig. 18 .

2004 Muhuathyris circularis new species; Sun et al. 2004b: 240–243, figs. 1–3.

Material.—Four ventral and six complete dorsal valves from sample MH 1; in addition 14 incomplete ventral and dorsal valves ranging from 4 to 25 mm in width.

Description.—The species was described in detail by Sun et al. (2004b).

Remarks.— Muhuathyris circularis is one of the most characteristic athyridid brachiopods in the fauna of the Muhua Formation. Its general morphology as well as details of a complex internal shell structure and its variability were discussed by Sun et al. (2004b). It differs from related Camarophorella Hall and Clarke, 1893 in the absence of a dorsal shoe lifter. From the similar genus Rowleyella Weller, 1911 the Chinese species differs in having two long subparallel vertical plates lateral to the dorsal median septum ( Fig. 18B, C ) and extending from the beak to the posterior edges of the dorsal adductor scars. However, these plates could be interpreted as rudimentary cruralium (see Sun et al. 2004b: 243) which in Rowleyella is well developed. According to Alvarez (2007) the subfamily affiliation of Muhuathyris is somewhat uncertain but our interpretation of the interior of the genus indicates that it can be placed within Rowleyellinae .

Stratigraphic and geographic range.—At present the species (and genus) is known from the type locality only.

Figures

Fig. 18. Meristelloid brachiopod Muhuathy− ris circularis Sun, Ma, Baliński, and Zhang, 2004 from the Tornaisian Muhua Formation, southern China. A. Incomplete ventral valve, PKUM02−0465, in general interior view (A1), enlargement of umbonal region showing left tooth (A2), and enlarged interior in slightly oblique view showing spondylium supported by median septum (A3). B. SEM micrograph of the interior of an incomplete dorsal valve, PKUM02−0466, in oblique−lateral view with labelled morphology (partly after Sun et al. 2004b: fig. 1−25). C. Incomplete dorsal valve, PKUM02−0467, in oblique view showing cardinalia. All from sample MH1.