Cupitheca convexa, Sun & Malinky & Zhu & Huang, 2018

Sun, Haijing, Malinky, John M., Zhu, Maoyan & Huang, Diying, 2018, Palaeobiology of orthothecide hyoliths from the Cambrian Manto Formation of Hebei Province, North China, Acta Palaeontologica Polonica 63 (1), pp. 87-101 : 92-95

publication ID	https://doi.org/ 10.4202/app.00413.2017
DOI	https://doi.org/10.5281/zenodo.10986492
persistent identifier	https://treatment.plazi.org/id/03C44804-FFA0-0C04-FFF5-97352B06DD2D
treatment provided by	Felipe
scientific name	Cupitheca convexa
status	sp. nov.

Treatment

Cupitheca convexa sp. nov.

Figs. 4–8.

Etymology: From Latin convexus, in reference to the convex nature of the interior of the operculum at the cardinal process area.

Type material: Holotype NIGPAS 166339a ( Fig. 6D View Fig ); Paratypes NIGPAS 166334, 166336–43 (Figs. 4, 6A–C) from the type locality.

Type locality: Zuojiawu section, Fengrun District of Tangshan City, Hebei Province, North China .

Type horizon: The purplish-red shales of the Manto Formation, Cambrian Stage 4/5.

Material. — Thirteen specimens in total, preserved as clusters of moulds of conchs and opercula (NIGPAS 166336– 39a, b, 166340, 166341a, b, 166342–47), and 3 specimens (NIGPAS 166375–77) preserved as inarticulate shells. All are decalcified.

Diagnosis.— Cupitheca with interior surface of operculum convex near cardinal processes; cardinal processes are moderately well-developed and bilobate; conch cyrtoconic; ornamentation on conch is merely transverse lines, and both interior and exterior surfaces of operculum covered by concentric ribs.

Description. —Conchs cyrtoconic with pronounced curvature, degree of curvature slightly varies in different specimens (Fig. 4A, C–E); transverse lines on exterior surface (Figs. 4A 3, 5A 7) with intervening spaces 2–15 μm wide; cross section circular to oval (Fig. 4B); apical angle of divergence small (14–16°); sculpture at apical termination varies ( Fig. 5A View Fig 4, A 5, B), with some having radial lines that probably represent the original microstructure of the shell ( Fig. 5A View Fig 4, A 5), while others possess a smooth terminus with no lines or other features ( Fig. 5A View Fig 1 –A View Fig 3 View Fig , A 6 View Fig , A 7 View Fig , C 3 View Fig ); and still others have irregularly radiating, branching ornamentation ( Fig. 5B View Fig ), which may be an artefact of preservation. A circumferential furrow separates the apical region from the remainder of the shell.

Operculum circular to sub-circular or slightly oval (opercular width and length are subequal, Fig. 7A View Fig ); protooperculum nearly flat ( Fig. 6A View Fig 2 View Fig , A 3 View Fig ) and circular ( Fig. 6A, B View Fig 1 View Fig , B 3 View Fig ), 250–530 μm in diameter ( Fig. 7A View Fig ), with a location toward the dorsal margin. Bilobate cardinal process can be observed near the dorsal margin of the operculum on the interior surface, forming a convex area and grading downward into a flattened marginal area ( Fig. 6B View Fig 4, C, D 1, D 3), impressions of cardinal processes can also be observed on the exterior of the operculum ( Fig. 6A, B View Fig 1 –B View Fig 3 View Fig ), which may be the result of high compression; these structures are generally rectangular in shape, and terminate at the distal end in a bluntly rounded surface. Angles of divergence of cardinal processes are 99–113° and 100° on average. Cardinal processes are Fig. 4. Cupithecid hyolith Cupitheca convexa sp. nov. from the Manto For- → mation (Cambrian Stage 4/5) in the Zuojiawu section of Tangshan, China.

A. NIGPAS 166334, accumulation of conchs and opercula (A 1), white arrows suggest discarded cylindrical segments, black arrows indicate opercula; three almost complete shells with apical parts buried in the matrix (A 2); transverse lines on the dorsal surface of conch (A 3); aggregation of skeletal parts with chaotic orientation (A 4). B. NIGPAS 166336, incomplete conch shows full aperture. C–E. More or less complete conchs. C. NIGPAS 166338.

D. NIGPAS 166340, two adjacent shells, the left one displays full apex (D 1); single conch with partial broken aperture (D 2). E. NIGPAS 166341b. Scale bars: A 1, 5 mm; A 2, C, 1 mm; A 3, 5 μm; B, 100 μm; A 4, D, E, 2 mm.

covered from proximal to distal terminations with scattered sub-circular pits (shown as tubercles on the counterparts; e.g., Fig. 6D View Fig ), 4–9 μm in diameter. Exterior of operculum is covered by a series of concentric lamellae or ribs ( Fig. 6A View Fig 1 View Fig , A 3 View Fig , B 1 –B View Fig 3 View Fig ). Interior also covered with concentric lines or ribs ( Fig. 6B View Fig 4, D 1, D 3) that correspond to those on the exterior.

Remarks. —Specimens of Cupitheca recovered from the Manto Formation on the North China Platform are distinctive from the more widely distributed and therefore better known C. holocyclata Bengtson in Bengtson et al., 1990 ( Bengtson et al. 1990; Skovsted et al. 2016) in terms of ornamentation of the conch and overall shape of the operculum. C. holocyclata from Australia ( Bengtson et al. 1990) and several individuals reported from North China from Cambrian Stage 4 ( Skovsted et al. 2016) have a dominant transverse ornament, with minimal to subordinate longitudinal overprint. In addition, the interior of the operculum of C. holocyclata is concave, while that of C. convexa sp. nov. is convex, and cardinal processes seen in C. holocyclata appear to be more robust than those of C. convexa sp. nov.. The protooperculum of the former is a circular elevated platform with a concave base and marginal rim ( Skovsted et al. 2016), which is different from the flattened and circular protooperculum in C. convexa sp. nov.. The new species is distinguished from C. costellata Xiao and Zhou, 1984 by possession of distinct longitudinal ornament in the latter. Our material also resembles C. manicae Duan, 1984 from the Lower Cambrian of Hubei Province, South China ( Duan 1984) in general morphology and cross section of the shell, but the latter possesses no ornament on the conch (possibly a taphonomic bias) and no known operculum, which makes detailed comparison difficult. This is also the case with the similar taxa C. brevituba Duan in Xing et al., 1984, C. intermedia ( Duan, 1984) , and C. mira (He in Qian, 1977) from the lower Cambrian of South China (Xiao and Zhou 1984; Duan 1984). These previous identifications as Cupitheca were based mainly on the ornament on the conchs, here we highlight the importance of the operculum in the classification of this group. The occurrence of C. holocyclata without opercula preserved should be questioned (see SOM 2).

The conch of specimen NIGPAS 166334 ( Fig. 8A View Fig ) possesses two distinct zones that are separated by a transverse discontinuity. The adapertural portion is characterised by transverse lines ( Fig. 8D View Fig ), whereas the adapical tapering zone is covered by longitudinal to sub-radial ornament ( Fig. 8C View Fig ). Although the apical termination cannot be well separated from the matrix, based on the distinct ornamentation covering of the two zones, the adapertural region is regarded as early juvenile portion of the conch, whereas the adapical portion is the presumed protoconch. Therefore the transverse discontinuity or furrow is possible the site where the first septum-like structure developed ( Bengtson et al. 1990). Furthermore, the diameter of the shell at the furrow is 450 μm, which overlaps with the ranges of diameters of the protoopercula in this collection ( Fig. 7C View Fig ). No weakening points or septum-like structures have been observed on the presumed protoconch. The ridge-like structure ( Fig. 8C View Fig ) seems to be deceptive, appearing as a biological structure, but in fact is most likely the result of mechanical damage because the outmost layer is squeezed to form an uneven ridge ( Fig. 8C View Fig ) rather than a dissolved groove ( Fig. 8B View Fig ). Although the apex is partially broken and peeled away, part of the lateral sub-radial lines could still be observed on the mould ( Fig. 8E View Fig ).

Stratigraphic and geographic range.—The Manto Formation, late Cambrian Series 2 Stage 4 or early Series 3 Stage 5, Hebei Province, North China (see SOM 2).