Actinoconchus sp.

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 : 813-814

Actinoconchus sp.

Fig. 14 .

Material.—Seven complete shells, 10 ventral, and 9 dorsal valves from sample MH1.

Description.—Shell transversely elliptical to oval in outline, subequally biconvex, sulcus and fold lacking. Ventral interior with short, subparallel and anteriorly divergent dental plates. Inside dorsal valve a small cardinal plate present, with small circular foramen, and postero−laterally bordered by elevated inner socket ridges (cardinal flanges; Fig. 14F ); low, sharp myophragm divides medially the dorsal adductor scars ( Fig. 14D 2). Externally with strong, widely distributed, concentric growth lines and flat, very long flanges; flanges do not disintegrate to spine−like projections, but are densely longitudinally striated ( Fig. 14D 4 , G).

Dimensions in mm, shell: length 7.1, width 8.8, thickness 4.7; largest complete ventral valve: length 9.8, width 12.2.

Remarks.— Xu and Yao (1988) described two new and two other species of Actinoconchus from the earliest Carboniferous of the Nanbiancun section, Guanxi Province, Southern China. The exterior of these species, as well as the details of ornamentation illustrated for three of those forms strongly suggest that they do not represent Actinoconchus but rather Cleiothyridina .

The species from Muhua are quite close externally to the type species of the genus, i.e., Actinoconchus paradoxus M’Coy, 1844 (see Brunton 1980) having similar shell shape but differing mainly in having less posteriorly protruding umbo of the ventral valve. The former are much less expanded

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

laterally than Actinoconchus expansus expansus (Phillips, 1836) and A. expansus patulus Brunton, 1980 but more wide than Actinoconchus oblongus (Sowerby, 1840) and Actinoconchus obtusus ( M’Coy, 1844) . Brunton (1980) placed provisionally A. obtusus in synonymy with A. oblongus . Several other lamellose athyridids similar to Actinoconchus but with persistent ventral sulcus were placed by Jin and Fang (1983) within genus Lamellosathyris Jin and Fang, 1983 .

Figures

Fig. 14. Athyridoid brachiopod Actinoconchus sp. from the Tornaisian Muhua Formation, southern China. A. Complete shell, PKUM02−0436, in dorsal (A1), ventral (A2), lateral (A3), and anterior (A4) views. B. Shell, PKUM02−0437, in dorsal (B1), ventral (B2), and anterior (B3) views. C. Ventral valve, PKUM02−0438, viewed from exterior (C1), and interior (C2). D. Dorsal valve, PKUM02−0439, in exterior (D1), interior (D2), and lateral (D3) views, and enlargement of the external lamellose ornamentation (D4). E. Incomplete ventral valve, PKUM02−0440, viewed internally (E1) and enlargement showing dental plates and muscle scars (E2). F. Umbonal region of a broken shell, PKUM02−0441, showing dental plates and cardinalia (dorsal valve below). G. Exterior of ventral valve, PKUM02−0442, showing well preserved long growth lamellae. All from sample MH1.

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).