Spiriferellina cf. insculpta (Phillips, 1836)

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 : 835-836

Spiriferellina cf. insculpta (Phillips, 1836)

Figs. 7B , 33 .

Material.—One complete and 2 damaged ventral valves, and one slightly incomplete dorsal valve from the sample MH2. One damaged dorsal valve and a fragment of ventral valve from the sample GB.

Description.—The single complete ventral valve is 7 mm long, 12 mm wide, and 6.4 mm thick, semicircular in outline, slightly subpyramidal in shape, with apsacline, high, almost flat, transversely striated triangular interarea; lateral margins of the interarea slightly rounded; cardinal extremities slightly rounded, hinge line almost equal the greatest width of the valve; sulcus very deep, rounded, bounded by a pair of very high, subangular plicae; delthyrium open, delthyrial angle 24 °.

Dorsal valve semicircular in outline, with a very high, an−

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

gular fold and tree high, angular plicae on each flank, diminishing in size rapidly toward lateral extremities; interarea low, almost linear, slightly concave, rectangular.

Ventral interior with short dental adminicula joining the valve floor in the umbonal region along the bottom of interspaces next to the sulcus−bounding plicae, continuing anteriorly as sharp lamellae decreasing gradually in height and becoming distally barely strong dental ridges; median septum thin, sharp, increasing in height anteriorly and reaching about the mid−valve.

Interior of dorsal valve with strong inner socket ridges diverging at 110 °; inner socket ridges and crural bases forming slightly concave plates, elevated above valve floor, and converging with the base of ctenophoridium; ctenophoridium distinct, subtriangular in dorsal view; adductor scars bordered by distinct ridges running more or less radially along the bottom of the fold−bounding interspaces.

Shell strongly plicate, 6 plicae on each of the two figured ventral valves ( Fig. 33A, D ), and 3 and 7 (including fold) on two dorsal valves, respectively ( Fig. 33B, C ). On a single dorsal valve two plicae bifurcate near the anterior margin ( Fig. 33C 1 ) but the bifurcation takes place anterior to a marked arrest of growth caused probably by some serious disturbance during the life of the animal. Concentric growth lamellae prominent, imbricate, with frequency of about 4 per mm; pustules nor observed, shell substance distinctly punctate.

Remarks.—The specimens from Muhua show great resemblance to Spiriferellina insculpta (Phillips, 1836) and Spiriferellina octoplicata (Sowerby, 1827) , both from the Lower Carboniferous of England and Ireland. The latter species are also morphologically similar to each other differing slightly mainly in the general shell outline and character of the shell plication ( North 1920; Brunton 1984; Bassett and Bryant 2006). Most of our specimens are very close to S. insculpta having the same number and shape of radial plicae ( Fig. 33A, B, D ). Only one slightly incomplete dorsal valve from Muhua shown on Figure 33C has at least 7 plicae thus resembling the condition of S. octoplicata . Unfortunately, the insufficient material does not allow for a satisfactory taxonomic comparison.

Stratigraphic and geographic range.— Spiriferellina insculpta is known from the Tournaisian–Viséan of the British Isles, Belgium, and doubtfully from the Moscow Basin of Russia (see Brunton 1984). Here we report similar form Tournaisian of Muhua, southern China.

Figures

Fig. 7. Shell encrustation in silicified brachiopods from the Tornaisian Muhua Formation, southern China. A. Chonetoid shell encrsuted by strophalosiidine Muhuarina haeretica Baliński and Sun, 2005, PKUM02−0080, (new photograph of specimens illustrated by Baliński and Sun 2008: fig. 1E and Sun and Baliński 2008: fig. 18C). B. Interior of dorsal valve of spiriferinide Spiriferellina cf. insculpta Phillips, 1836, PKUM02−0388, in general (B1) and enlarged (B2) views showing infestation by endobiont Haplorygma dorsalis Baliński and Sun, 2010b (see also Baliński and Sun 2010b: fig. 1A; new photographs). C. SEM micrographs of dorsal valve of spiriferide Tylothyris laminosa (M’Coy, 1841), PKUM02−0389, showing infestation by H. dorsalis in general (C1) and enlarged (C2) views (see also Baliński and Sun 2010b: fig. 1B; new photographs). Samples GB (A, B) and MH1 (C).

Fig. 33. Spiriferinidine brachiopod Spiriferellina cf. insculpta (Phillips, 1836) from the Tornaisian Muhua Formation, southern China. A. Ventral valve, PKUM02−0578, in exterior (A1) and interior (A2) views. B, C. Two incomplete dorsal valves, PKUM02−0579 (B) and PKUM02−0388 (C, same as in Fig. 7B), in exterior (B1, C1) and interior (B2, C2) views, and enlargement of cardinalia (C3). D. Ventral valve, PKUM02−0580, in exterior (D1), interior (D2), and posterior (D3) views. Sample MH2 (A, B, D) and GB (C). Scale bars 2 mm.

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).