Kuqaia Li, 1993

Genus Kuqaia Li, 1993 emended.

1993 Kuqaia Li , pp. 72, 74.

Type species. Kuqaia quadrata Li, 1993 .

Emended diagnosis. Shell single-layered, bilaterally symmetrical, splitting along venter. Shell surface ornamented with a series of concentric and/or radial ridges. Concentric and radial ridges initiate on the ventral side. Caudal end tapered, acute. Peduncles variably present on the postventral sides.

Remarks. The diagnosis of Kuqaia is here emended to encompass characters of Kuqaia scanicus sp. nov., i.e., the presence of two lateral peduncles at the caudal end ( Figs 2 View Fig 2 and 3 View Fig 3 ).

Three species of Kuqaia were originally defined from the Mesozoic of China based on surface ornamentation: Kuqaia quadrata , characterized by “checked ornamentation”, K. concentrica , having “concentrical ridges thicker than radial ones”, and K. radiata , with “well-developed radial ridges” ([ 18], pp. 74–75). Two additional species were subsequently established: K. yangii , characterized by “concentric ridges on dorsum and venter and radial ridges on lateral sides”, and K. yanqiensis, having a “weakly ornamented or smooth shell surface” ([ 25], p. 303). Aneules cucuma was also transferred to Kuqaia [ 25]; however, identification of this species is problematic owing to the discrepancy between the illustration of the holotype and its description ([ 19]; Fig 4 View Fig 4 ).

Although several species have been described ( Fig 4 View Fig 4 ), Kuqaia quadrata has been applied in a broad sense to all Kuqaia specimens recorded from the Norwegian offshore Jurassic strata based on the ornamentation in that population varying according to the contrasting degree and angle of compaction, and the quality of preservation [ 28]. Although some intraspecific variation is expected in the ornamentation of ephippia, we assign Kuqaia specimens to several discrete species, since there are clear visible differences among specimens regarding the pattern and robustness of shell surface ornamentation.

Among other acid-resistant mesofossil groups, the putative seed membrane Chrysotheca diskoensis Miner, 1935 , with “oblong-ovate” body shape, bearing “3–6 plicate [sic] to the base, sessile or apparently short stalked” ornamentation on the body ([ 35], p. 590), has superficial morphological similarities to Kuqaia concentrica in bearing a predominance of concentric ridges. A later record of Chrysotheca diskoensis possesses transverse, although very thin and indistinct, ridge-like structures ([ 36], fig 36), which are somewhat similar to the ornament of Kuqaia quadrata but they encompass much larger lumina. Specimens of the dispersed seed membrane Spermatites reticulatus Kutluk & Hills, 2017 are also similar to Kuqaia quadrata in their possession of a raised reticulum/chequered ridges forming square and rectangular lumina, and some have a short stalk at the base of the main body [ 37]. However, Spermatites has radial symmetry and likely represents the megaspore membrane or inner testa coat of a seed-plant.