Spiriferellinidae Ivanova, 1972

Sun, Zuoyu, Hao, Weicheng, Sun, Yuanlin & Jiang, Dayong, 2009, Silicified Anisian (Middle Triassic) spiriferinid brachiopods from Guizhou, South China, Acta Palaeontologica Polonica 54 (1), pp. 61-68 : 63-65

publication ID	https://doi.org/ 10.4202/app.2009.0107
persistent identifier	https://treatment.plazi.org/id/03E42D4F-DA76-FE05-FF35-FB2277FBFDBD
treatment provided by	Felipe
scientific name	Spiriferellinidae Ivanova, 1972
status

Treatment

Family Spiriferellinidae Ivanova, 1972 View in CoL Genus Pseudospiriferina Yang and Xu, 1966

Type species: Pseudospiriferina variabilis Yang and Xu, 1966 ; Middle Triassic of Guizhou (South China) .

Pseudospiriferina multicostata Yang and Xu, 1966 View in CoL Figs. 2 View Fig , 3A–H View Fig .

1966 Pseudospiriferina multicostata View in CoL sp. nov.; Yang and Xu 1966: 45–47, pl. 6: 2, 3.

Material.—27 articulated shells, 278 ventral and 387 dorsal valves.

Dimensions.—L = 12.0 mm; W = 16.0 mm; H = 8.0 mm (GMPKU−P−6145, Fig. 3A View Fig 1 –A View Fig 3 View Fig ).

Emended diagnosis (modified from Yang and Xu 1966).— This species differs from all other representatives of the genus Pseudospiriferina and the other spiriferellinid genera by its small size (rarely exceeding 10 mm), fold with median groove, sulcus with median costa, and more numerous and finer costae on the flanks.

Description.—Shell small to medium−sized, generally up to 10 mm in length, with the width−to−length ratio of about 1.3 ( Fig. 2 View Fig ), transversely spiriferoid and ventribiconvex in outline. The maximum width of the shell at the hinge line or slightly posterior to it, which is straight. Cardinal extremities usually subangular ( Fig. 3B View Fig 1, D 1, E 1 View Fig ), occasionally obtuse.

Ventral valve moderately convex, varying from broadly triangular to semicircular in outline, with a small acute, incurved beak. Ventral interarea transverse triangular, apsacline, with numerous transverse striations with the exception of narrow and slightly concave triangular areas flanking delthyrium. Delthyrium open, its width attaining about 1/4 of the hinge line. Anterior commissure sulciplicate, with a distinct tongue ( Fig. 3B View Fig 2 View Fig ). Sulcus well developed, twice as wide as the interspaces between costae on flanks, with one intercalated median costa ( Fig. 3A View Fig 1, B 1, C 1 View Fig ).

Dorsal valve gently convex with semicircular outline. Dorsal interarea very low, about 2 mm in height, orthocline. Fold moderately developed, slightly higher than costae on the flanks, much more prominent near the anterior margin, with a characteristic narrow median groove dividing the fold into two plicae ( Fig. 3A View Fig 2 View Fig , A 3 View Fig , C 2 View Fig , C 3 View Fig , D 1, E 1, F 1 View Fig ).

Costae begin near the umbo, widen anteriorly. Costae on the flanks narrow, triangular in cross section, separated by interspaces of similar width; usually about 6 costae on each flank. Costa close to the fold or the sulcus occasionally bifurcating anteriorly ( Fig. 3B View Fig 1, E 1 View Fig ). Growth varices subimbricate, which are crowded near the anterior margin of both valves ( Fig. 3A View Fig 1 View Fig , A 3 View Fig , B 1 View Fig , C 3 View Fig , D 1, E 1 View Fig ), occasionally throughout the whole valve ( Fig. 3F View Fig 1 View Fig ).

Ventral interior with the blade−like median septum originating from the umbonal thickening and extending to about one−third of the valve length ( Fig. 3B 3 View Fig , B 4 View Fig ). Dental plates divergent, reaching the floor of the valve near the beak, and continuing anteriorly as about 1 mm deep dental flanges. Dental plates and median septum discrete, posteriorly much thickened with callus ( Fig. 3B View Fig 4 View Fig ).

Dorsal valve interior with small−sized and trough−like sockets ( Fig. 3D View Fig 2 View Fig , D 3 View Fig , F 2 View Fig , F 3 View Fig , H). Inner socket ridges together with crural bases form subtriangular plates that connect with each other behind the ctenophoridium (i.e., cardinal process). Ctenophoridium is relatively large and well developed as an outgrowth of the secondary shell apically between the inner socket ridges. It is striated, triangular in cross section, and swollen anteriorly ( Fig. 3E View Fig 2 View Fig , E 3 View Fig , F 2 View Fig , F 3 View Fig ). Dorsal median septum and septalium not developed. Crura rather short, subparallel to slightly medially convergent, frequently with preserved short, broken, submedially directed jugal processes ( Fig. 3E View Fig 2 View Fig , G, H). Remarks.—Our examined specimens are evidently conspecific with Pseudospiriferina multicostata Yang and Xu, 1966 in their relatively small shell size, having median costa in the sulcus and median groove on the fold, and more numerous and finer costae on flanks in comparison to other species of Pseudospiriferina . These characters also allow us to distinguish them from other co−occurring species of Punctospirella . It is noteworthy that P. multicostata was originally established by Yang and Xu (1966) on only three articulated shells and four fragments coming from the Middle Guanling Formation at the Qingyan section of Guiyang, while the very abundant and well−preserved silicified valves herein substantially added the knowledge of the internal features of P. multicostata as described above. Morphological changes in the growth varices, the cardinal extremities, and the bifurcation of the costa near the fold ( Fig. 3B View Fig 1, E 1 View Fig ) are interpreted as intraspecific variations.

Stratigraphic and geographic distribution.— Middle and Upper Member of the Guanling Formation, Middle Anisian, from Qingyan, Guiyang, central Guizhou , and Xinmin, Panxian, western Guizhou, China .