Halysestheria biformis Zhang & Chen

LI, GANG, 2021, Taxonomy of the clam shrimp Halysestheriidae (Diplostraca: Spinicaudata) from the Upper Cretaceous Nenjiang Formation in central Dayangshu Basin of eastern Inner Mongolia, northeastern China, Palaeoentomology 4 (2), pp. 156-164 : 158-159

Halysestheria biformis Zhang & Chen in Zhang et al., 1976 emend.

( Figs 2–5 )

1976 Halysestheria biformis Zhang & Chen in Zhang et al., p. 211, pl. 91, figs 1–2; pl. 92, figs 1–4; pl. 93, fig. 8.

1985 Halysestheria biformis Zhang & Chen (in Zhang et al., 1976), Chen & Shen, p. 133, pl. 13, figs 1–2.

Emended diagnosis. Carapace moderate in size; elliptical, long oval or subquadrate in outline; umbo located in the anterior part of the dorsal margin. Growth lines are serrated in the lower margins. Growth bands in the umbonal area ornamented with widely spaced radial lirae, intercalated with fine reticulation and puncta; growth bands in the ventral part of the carapace ornamented with chain-like reticulation, which appears as radially aligned, discontinuous, short, fine ridges on external mould.

Locality and horizon. Jilin Province, and Ganhe, OroqenAutonomous Banner, Inner Mongolia,northeastern China; First Member of the Upper Cretaceous Nenjiang Formation .

Description. Carapace moderate in size, elliptical, long oval, or subquadrate in outline. Anterior margin widely rounded, posterior margin pointed. Umbo located in the anterior part of the dorsal margin. Growth lines prominent, 20–30 or more in number, serrated along their lower margins ( Figs 2E , 3B, E, G , 4A ). Growth bands narrow in the umbonal area, become wider in the middle part of the carapace ( Figs 2A , 5E–H ); those in the ventral part of the carapace become narrower again. Growth bands near the umbo ornamented with widely spaced long radial lirae, which are simple or branched, intercalated with fine reticulation, puncta occur within the fine mesh ( Figs 2B , 3C ). Growth bands in the ventral part of the carapace, radial lirae are thickened, fine mesh between the lirae are radially aligned to form chain-like ornamentation ( Figs 2F , 3H , 4D, F, H ), which appears as radially aligned, discontinuous, short, fine ridges on external mould ( Figs 2E , 3G , 4C, E, G ). Growth bands in the antero-ventral part of the carapace are almost smooth with some pits in the lower part of each band ( Fig. 3F ).

Dimensions. In order: specimen no., number of growth bands, length (mm), height (mm), height/length ratio: NIGP27106, 26, 6.8, 4.6, 0.67; NIGP174748, 31,8.4, 5.9, 0.71; NIGP174749, 33, 7.7, 5.3, 0.7; NIGP174750, 25, 8.5, 5.9, 0.69; NIGP 174751, 21, 7.8, 5.2, 0.67; NIGP 174752,>14, 9.2, 6.8, 0.74; NIGP174753, 34, 7.5, 4.7, 0.63; NIGP174754,>21, 7.3, 4.6, 0.64; NIGP174755, 26, 7.0, 4.3, 0.61; NIGP174756, 25, 7.6, 5.1, 0.66; NIGP174757, 22, 7.7, 4.6, 0.60.

Remarks. In order to make a comparison, the holotype specimen of the type species (an external mould of a right valve) was also examined under the SEM ( Fig. 2B–F ). Although the specimen was varnished in order to protect it, clear micrographs have been taken from growth bands near the umbo ( Fig. 2B, D ) and in the ventral part of the carapace external mould ( Fig. 2E ). Clear widely spaced radial lirae with intercalated reticulation and puncta in the dorsal part of the carapace, and a chain-like ornamentation occurs on growth bands in the ventral part of the carapace.

The specimens from Inner Mongolia have elliptical, long oval or subquadrate outline, the height/length ratio between 0.61 and 0.74. In consideration of the sex dimorphism, the long oval form may be male, and subquadrate form may be female.

Except for the type species, several other species have also been described from the First Member of the Nenjiang Formation, such as Halysestheria ovata ( Chang, 1957) , H. qinggangensis Chen in Zhang et al., 1976, H. rhombica Zhang & Chen in Zhang et al., 1976, H.? sublineata Zhang & Chen in Zhang et al., 1976, H. subquadrata Zhang & Chen in Zhang et al., 1976, H. subtermina ( Chang, 1957) , H. yui ( Chang, 1957) . Li (2005) considered that H. qinggangensis and H. subtermina are junior synonyms of H. yui , the former two species have an elliptical carapace, and H. yui has a rounded carapace. The rounded carapace may be female, and the elliptical carapace may represent the male. While the H.? sublineata, having a long oval carapace, was named basing on only one specimen.It could be a junior synonym of the type species. H. subquadrata has a subquadrate carapace, which associates with H. yui , H. ovata and H. subtermina ( Zhang et al., 1976) , thus, may be they are the same species. H. rhombica is similar with the type species, and was named basing on only one broken specimen. It could be a junior synonym of the type species.

Figures

FIGURE 2. Halysestheria biformis Zhang & Chen in Zhang et al., 1976 emend.All are SEM images except A, which is a light micrograph. The specimen was collected from the First Member of the Upper Cretaceous Nenjiang Formation in Jilin, northeastern China. A, An external mould of a right valve, holotype NIGP27106. B, The furrows intercalated nodular platform on a growth band near the umbo. C, A reverse image of B, widely spaced radial lirae with intercalated reticulation and puncta, lirae simple or branched. D, Widely spaced furrow with intercalated nodular platform on growth bands near the umbo. E, Radially aligned, discontinuous short ridges or nodules on growth bands in the ventral part of the carapace external mould, and serration along the lower margins of growth lines. F, A reverse image of E, showing the dense radial lirae with intercalated chain-like ornamentation on growth bands in the ventral part of the carapace, growth lines with serrated lower margins. Scale bars are 1 mm in A; 20 µm in B, C; 100 µm in D–F.

FIGURE 3. Halysestheria biformis Zhang & Chen in Zhang et al., 1976 emend. All are SEM images. The specimen is from the First Member of the Upper Cretaceous Nenjiang Formation at Ganhe, Oroqen Autonomous Banner of Inner Mongolia, northeastern China. A, An external mould of a right valve, NIGP174748. B, A reverse image showing widely spaced radial lirae with intercalated reticulation and puncta on growth bands near the umbo, lirae simple or branched. C, Widely spaced furrow with intercalated nodules on growth bands in the anterodorsal part of the carapace external mould. D, A reverse image of C, showing widely spaced radial lirae with intercalated reticulation and puncta. E, Sparse nodules along the lower part of each growth band in the anteroventral part of the carapace, growth lines are serrated in the lower margins. F, A reverse image of E, showing almost smooth growth bands with pitted ornament along the lower part of each growth band in the anteroventral part of the carapace. G, Radially aligned discontinuous short ridges on a growth band in the ventral part of the carapace external mould, growth lines with serrated lower margins. H, A reverse image of G, showing thickened radial lirae with intercalated chain-like ornament on growth band in the ventral part of the carapace. Scale bars are 1 mm in A; 10 µm in C, D; 20 µm in B, E–H.

FIGURE 4. Halysestheria biformis Zhang & Chen in Zhang et al., 1976 emend. All are SEM images of the specimen of Fig. 3A. A, Widely spaced furrows with intercalated nodules on a growth band in the posterodoral part of the carapace external mould. B, A reverse image of A, showing widely spaced radial lirae with intercalated reticulation and puncta on a growth band in the posterodoral part of the carapace. C, Radially aligned nodules on a growth band in the posteroventral part of the carapace external mould. D, A reverse image of C, showing thickened radial lirae with intercalated chain-like ornament on a growth band in the ventral part of the carapace. E, Radially aligned nodules on growth bands in the posteroventral part of the carapace external mould. F, A reverse image of E, showing dense radial lirae with intercalated chain-like ornament on growth bands in the posteroventral part of the carapace. G, Radially aligned discontinuous short ridges or nodules on growth bands in the ventral part of the carapace external mould. H, A reverse image of G, showing dense and thickened radial lirae with intercalated chain-like ornament on growth bands in the ventral part of the carapace. Growth lines with serrated lower margins. Scale bars are 10 µm in A, B; 20 µm in C, D; 100 µm in E–H.

FIGURE 5. Halysestheria biformis Zhang & Chen in Zhang et al., 1976 emend. All are light micrographs of specimens form the First Member of the Upper Cretaceous Nenjiang Formation of Ganhe, Oroqen Autonomous Banner, Inner Mongolia, northeastern China. A, An external mould of a left valve, NIGP174749. B, A left valve, NIGP174750. C, The left one: a left valve, NIGP174751; the right one: an external mould of a right valve, NIGP174752. D, An external mould of a left valve, NIGP174753. E, An external mould of a right valve, NIGP174754. F, External moulds of articulated two valves, NIGP174755. G, Displace valves, NIGP174756. H, Articulated valves, NIGP174757. Scale bars = 1 mm.