Revision of Triplicatella (Orthothecida, Hyolitha) with preserved digestive tracts from the early Cambrian Chengjiang Lagerstätte, South China

Abstract

The cap-shaped shells of Triplicatella are known almost exclusively from small shelly fossil assemblages with articulated specimens showing unequivocally that they represent the operculum of a hyolith. Abundant specimens of Triplicatella opimus from the fine-grained shales of the Chengjiang Lagerstätte of South China with soft-part preservation are documented herein. The soft tissues, including the feeding apparatus and complex digestive system, in T. opimus strongly suggest that Triplicatella was a deposit feeder. The digestive tract of T. opimus consists of two limbs, a spiral loop folded into a chevron-like structure and a slightly recurved to straight anal tube, which are preserved as reddish-black traces enriched in iron. The new anatomical information obtained from T. opimus in the Chengjiang Biota suggests an intermediate stage in the development of the characteristic folded gut of orthothecid hyoliths. The new anatomical information reported here shows that Triplicatella is one of the best-preserved early members of the Orthothecida and promotes our understanding of the general anatomy and evolution of the Hyolitha.

Hyolithid-like hyoliths without helens from the early Cambrian of South China, and their implications for the evolution of hyoliths

“…All specimens from the Chengjiang biota however come from mudstones and hence have undergone high levels of compaction and the specimens show small deformations on both conch and opercula. Some specimens preserved as imprints do show the remains of some red organic stains (that have been interpreted as the remains of soft tissue in other Chengjiang hyolith taxa; see [ 8 , 9 ]), while other specimens are preserved as internal moulds, with conch and operculum still articulated. Despite the mode of preservation, similarities, particularly in the morphology of opercula, displaying unique clavicles formed by a palisade arrangement of sub-parallel rods and a sharp conical-pyramidal conch with rounded lateral margins (Figs.…”

“…The establishment of Paramicrocornidae and the wealth of new data recently reported on hyolith taxonomy and morphology [ 7 – 9 , 13 , 14 , 18 – 21 , 26 , 55 , 56 ] necessitates an overhaul of hyolith interrelationships and for this purpose we performed a phylogenetic analysis based on Cambrian and Ordovician hyolith taxa (Figs. 6 , 7 , Additional file 1 : Fig.…”

“…Hyoliths are generally subdivided into two distinct groups, the Hyolithida and Orthothecida [ 3 ]. Orthothecids appear first in the fossil record and are usually composed of two simple skeletal components, a conical conch with a variable cross section and a flat, retractable operculum [ 4 – 9 ]. In contrast, hyolithids typically consist of four skeletal components, a cone-shaped conch, an externally fitting and folded operculum with distinct cardinal and conical shields, and a pair of curved spine-shaped helens [ 10 – 15 ].…”

“…Hyoliths are among the most numerous biomineralizing animals in the Chengjiang Lagerstätte and some taxa have been systematically described [ 8 , 9 , 21 ]. In this study, we examine new material of a small hyolith from the Chengjiang biota (Cambrian Series 2); originally described by Qian [ 22 ] as Ambrolinevitus ventricosus Qian, 1978 .…”

New insight into the soft anatomy and shell microstructures of early Cambrian orthothecids (Hyolitha)

“…R. Soc. B 287: 20201467 forms in the early Cambrian [25,26]. The new orthothecid Longxiantheca mira gen. et sp.…”