Changshunella yangi, Sun & Baliński & Ma & Zhang, 2004

Sun, Yuanlin, Baliński, Andrzej, Ma, Xueping & Zhang, Yubo, 2004, New bizarre micro-spiriferid brachiopod from the Early Carboniferous of China, Acta Palaeontologica Polonica 49 (2), pp. 267-274 : 269-273

publication ID	https://doi.org/ 10.5281/zenodo.13507972
persistent identifier	https://treatment.plazi.org/id/49378797-FFD0-4B06-261C-FC07FEF09FD9
treatment provided by	Felipe
scientific name	Changshunella yangi
status	gen. et sp. nov.

Treatment

Changshunella yangi gen. et sp. nov.

Figs. 2–6 View Fig View Fig View Fig View Fig View Fig .

Holotype: Dorsal valve PKUM02−0035 illustrated on Fig. 3C View Fig . Other materials examined: 18 ventral valves and 30 dorsal valves.

Type locality and horizon: Muhua III section, Muhua , Changshun County, Guizhou, China ( Fig. 1 View Fig ; see also Hou et al. 1987: 11, fig. 3). The GPS coordinator is N 25 ° 47’59'' and E 106 ° 24’11''. About 0.2 m above the base of the Muhua Formation, conodont crenulata Zone (middle Tournaisian) GoogleMaps .

Etymology: This species is named for the late Professor Shifu Yang, of the Chinese Geological University at Beijing, in recognition of his contributions to the study of the Carboniferous brachiopods of Southern China.

Diagnosis.—Shell small, transverse and ventribiconvex with denticulate hinge line; maximum width at hinge line. Ventral valve hemipyramidal with a very high and flat, procline, triangular ventral interarea. Delthyrium narrowly elongate triangular, at least apically covered by convex pseudodeltidum. Dorsal valve gently convex, transverse triangular to trapezoidal in outline. Both valves medially plicate, with three prominent round to medially grooved plications on dorsal valve and three compound plications on ventral valve. Flanks generally smooth. Ornament of growth lamellae only. Ventral interior with dental ridges. A short median ridge may be present apically. Dorsal interior with well−developed ctenophoridium; crural plates or dorsal adminicula and median septum lacking.

Description.—The shell is small in size, generally 2.6–4 mm in length and 5–8 mm in width, transverse and ventribiconvex. Ventral valve is broadly triangular in outline ( Fig. 2A View Fig 3 View Fig , B 2 View Fig , B 3 View Fig , H 1 View Fig ) with a very high, vertically striated ventral interarea that is moderately to strongly procline ( Fig. 2A View Fig 1 View Fig , A 4 View Fig , D, G 1 View Fig , H 3 View Fig , J 2 View Fig , K 3 View Fig ). The ventral interarea is strikingly flat, transverse triangular, with height generally larger than the length of the valve; beak is minute. Most part of the ventral interarea bears vertical striation except the triangular areas lateral to the delthyrium ( Figs. 2A View Fig 5 View Fig , D, 4A View Fig ). The cardinal angles are acute. Slopes of the ventral valve are slightly concave to make the valve hemipyramidal in form ( Fig. 2A View Fig 4 View Fig , K 1 View Fig ). In lateral profile the valve is usually slightly concave ( Fig. 2A View Fig 4 View Fig , C 1 View Fig , I 4 View Fig ). In some specimens the posterolateral slopes merge with lateral edges of the ventral interarea to form cavity−free, thin−bladed extensions ( Fig. 2B 2 View Fig , F). The delthyrium is narrowly elongate triangular with an apical angle about 18–21°. Although a convex pseudodeltidum is observed in all ventral valves only to cover two−fifth to half of the delthyrium apically, it is possible that it may, in fact, fully cover the delthyrium because in several specimens remnants of the plate can be traced along the edges of the delthyrium ( Fig. 2A View Fig 1, G 1 View Fig ).

Dorsal valve is gently convex, transverse triangular to trapezoidal in outline. Dorsal interarea is narrowly rectangular, flat or curved, orthocline in less convex specimens ( Fig. 3E–G, H View Fig 2 View Fig ) and apsacline in gently convex specimens ( Fig. 3C View Fig 4 View Fig , D 3 View Fig ), with width/height ratio of 23–28. Both valves are medially plicate.

The general development of plications on the ventral valve is very peculiar. The valve bears three round major plicae each composed of a pair of subordinary plicae ( Figs. 4B, E View Fig , 5A View Fig ). The medial four subordinary plicae originate by bifurcation from two wide and flat primary plicae separated by a very narrow but deep interspace in the umbonal region ( Fig. 2A View Fig 3 View Fig , B 1 View Fig , C 2 View Fig , I 5 View Fig , K 1 View Fig ). There are also two lateral plicae, one on each flank of the valve, that are intercalated slightly later than the bifurcations of the primary plicae ( Fig. 5A View Fig ). The inner branch of each primary plica runs anteriorly very close to the other to form a single and high compound median plication ( Fig. 2A View Fig 3 View Fig , B 1 View Fig , C 2 View Fig ); the interspace between the primary plicae continues anteriorly as a longitudinal groove on the top of the compound median plication. On the other hand, the outer branch of each primary plica extends forward divergently and adheres to the nearby simple intercalated lateral plica to form a medially grooved compound lateral plication. The interspaces between the lateral and median compound plications are rather profound and wide. Besides the lateral compound plication, flanks of the ventral valve are generally smooth but occasionally a weak and simple additional plication is developed ( Fig. 2B 2 View Fig ). Several ventral valves show evidence of growth deformation of external features ( Fig. 2E View Fig ).

The dorsal valve is covered medially with three prominent plications. Compared to the ventral plications, these on dorsal valve are developed from dorsal beak region independently ( Figs. 3A 3 View Fig , C 2 View Fig , D 4 View Fig , J 1, K 1 View Fig , 5B View Fig ). The median plication is very high, relatively narrow and carinate posteriorly, becoming wider and round anteriorly, occasionally with a shallow median furrow ( Fig. 3C View Fig 5 View Fig ). On some specimens the median plica attains great height anteriorly ( Fig. 3C View Fig 1 View Fig , C 2 View Fig , H 1 View Fig ) being slightly constricted at its base; it must have been produced by distinct outward plication of the mantle ( Fig. 3E, F, J View Fig 2 View Fig ) which later during the growth was withdrawn during simultaneous infilling of the emptied space with secondary shell material ( Figs. 3E, F, G View Fig 1 View Fig ). The lateral plicae are usually medially grooved with a weak and shallow median furrow on them ( Fig. 3C View Fig 2 View Fig , C 5 View Fig , D 2 View Fig , D 4 View Fig , H 1, J 1, K 1 View Fig ). In our collection, only two dorsal valves have none of the plications medially grooved and two specimens have all plications medially grooved. The interspaces between the lateral and median plications are very deeply concave. Lateral slopes of the dorsal valve are smooth. Although all the specimens are preserved as disarticulated valves, judging from the width of the plications and interspaces at the anterior margin it seems obvious that the dorsal plications are arranged in opposed folding with their counterparts on ventral valve, forming a trilobate anterior margin ( Fig. 4B, D View Fig ). The presence of a median furrow or sulcus in the apical region of the ventral valve (i.e., in early juvenile stage) would suggest that this opposed folding may be derived from a bilobate stage. Surfaces of both valves are covered with growth lamellae.

Ventral valve interior reveals well−developed dental ridges ( Fig. 2F, G 2 View Fig , J 1 View Fig , J 3 View Fig , K 2 View Fig ), but no dental plates or dental adminicula. Some specimens show a short median ridge at the posterior of the valve floor ( Fig. 2J View Fig 3 View Fig ) and others do not have this feature.

Dorsal valve interior reveals triangular to subcircular conical sockets. Inner socket ridges are high forming with crural bases subtriangular plate−like structures. The crural bases are antero−ventrally directed. The spiralium is not preserved. The cardinal process is relatively large and developed as an outgrowth of the secondary shell apically between the inner socket ridges ( Fig. 3D View Fig 6 View Fig , H 4 View Fig , I). In some specimens the cardinal process is bilobate ( Fig. 3I View Fig ) or knoblike while in others it is striated ( Fig. 3B, D View Fig 6 View Fig ); this is probably a result of preservation. It is likely that the cardinal process of the new genus and species is both bilobate and striated ( Fig. 6 View Fig ). There are neither crural plates nor median septum. In most specimens the reflection of the negative relief of plications and interspaces on the internal surface of the valve is generally indistinct, at least not as obvious as that of external surface except in the most anterior portion of the median plication ( Fig. 3C View Fig 4 View Fig , D 3 View Fig , G 1 View Fig , H 2 View Fig ). Only in three dorsal valves we observed a prominent trough−like median furrow corresponding to the external median plication ( Fig. 3E, F, K View Fig ).