Vicissicaudata Ortega-Hernández, Legg, and Braddy, 2013

Zhu, Yuyan, Zeng, Han, Liu, Yao & Zhao, Fangchen, 2023, New artiopodan euarthropods from the Chengjiang fauna (Cambrian, Stage 3) at Malong, Yunnan, China, Acta Palaeontologica Polonica 68 (3), pp. 427-440 : 433-437

publication ID	https://doi.org/ 10.4202/app.01080.2023
persistent identifier	https://treatment.plazi.org/id/038B87F0-2F50-D349-6FEE-F8E4FC09BEA4
treatment provided by	Felipe
scientific name	Vicissicaudata Ortega-Hernández, Legg, and Braddy, 2013
status

Treatment

Superclass Vicissicaudata Ortega-Hernández, Legg, and Braddy, 2013

Order and family incertae sedis

Genus Sidneyia Walcott, 1911

Type species: Sidneyia inexpectans Walcott, 1911 , Walcott Quarry , Fossil Ridge , British Columbia, Canada; the Phyllopod Bed, Burgess Shale Formation .

Emended diagnosis.—Cephalon consisting of a rectangular dorsal shield with large hypostome, lateral cephalic notches for accommodation of stalked eyes and antennae, and three pairs of isomorphic post-antennal appendages. Thorax of eight to ten articulating tergites, each of which bears a pair of biramous limbs. Abdomen of one to three cylindrical sclerites and a telson with a pair of tail flukes (emended from Du et al. 2023).

Remarks.—With the recent discovery of S. minor from the lower Cambrian Hongjingshao Formation of Yunnan, China ( Du et al. 2023), the diagnosis of the originally monospecific Sidneyia was updated to accommodate the morphology of S. minor . As the new species established here is resolved as a sister species to the two other species of Sidneyia (see below), the diagnosis of Sidneyia is emended by incorporating the morphology of this new species, which includes different numbers of thoracic tergites and abdominal segments.

Sidneyia malongensis sp. nov.

Figs. 3 View Fig , 4 View Fig .

ZooBank LSID: urn:lsid:zoobank.org:act:4BDFA80F-1323-4748-BBB6-4A5846D9ED00

Etymology: After Malong District where the fossil was discovered.

Type material: Holotype, specimen preserving complete abdomen and most part of cephalon and thorax, part only, NIGP 200051 View Materials ( Fig. 3 View Fig ) . Paratype, specimen preserving complete abdomen, most part of thorax, and a small part of cephalon only, part only, NIGP 200052 View Materials ( Fig. 4 View Fig ) .

Type locality: Kuangshan section, Malong, Yunnan, China .

Type horizon: Maotianshan Shale Member, Yu’anshan Formation, Wutingaspis –Eoredlichia Trilobite Zone, Cambrian Series 2, Stage 3.

Material.— Type material only.

Diagnosis.—A species of Sidneyia with eight imbricated tergites in thorax and two cylindrical segments in abdomen.

Description.—Oval-shaped exoskeleton is composed of cephalon, thorax, and abdomen. Body length is about 31 mm in the holotype, and the maximum width is about 21 mm in the holotype and 15 mm in the paratype.

Cephalon is semi-elliptical, measuring 6 mm long and 17 mm wide in holotype ( Fig. 3A 3 View Fig : ce). Anterior margin of cephalon is rounded, and posterior margin of cephalon is straight. Lateral eyes are located at genal angles of cephalon ( Fig. 3B View Fig : e). Eyes are associated with notches on cephalon, but eye stalks are unclear ( Fig. 3B View Fig : n). Presence of numerous wrinkles near the anterior margin indicates the convexity of the cephalon.

Thorax consists of eight imbricated tergites of approximately equal length, measuring 16 mm long in holotype and 12 mm long in paratype. Overlapping area between adjacent thoracic tergites accounts for about one third of sagittal length of tergite. Posterior margin of the first to three thoracic tergites is almost straight. Thorax is widest at the third or fourth thoracic tergite, measuring 8 mm wide in holotype, after which it gradually narrows and curves posteriorly ( Figs. 3A 3 View Fig , 4A View Fig 3 View Fig : t1–t8). Pleural angle of each tergite is nearly equal along thorax. No marginal spines are found on thoracic tergites.

Abdomen consists of two overlapping cylindrical segments of subequal dimensions, measuring 4 mm long and 4 mm wide in holotype, and a tail fluke ( Figs. 3A 3 View Fig , D, 4A View Fig 3 View Fig , C: as, tf). Abdominal segments are narrower than the last thoracic tergite. Overlapping area between adjacent abdominal segments accounts for about one-fifth to one-fourth of sagittal length of segment, with an average length of 1 mm. Tail fluke consists of a central triangular telson and a pair of flanked flaps, which is approximately as long as abdominal segments ( Figs. 3A 3 View Fig , D, 4A View Fig 3 View Fig , C: tf).

Remarks.— Sidneyia malongensis sp. nov. shares some common features with S. inexpectans from the Burgess Shale and S. minor from the Hongjingshao Formation, such as a semicircular cephalon, a similar overlapping degree of tergites and a cylindrical abdomen ( Bruton 1981; Stein 2013; Zacaï et al. 2016; Du et al. 2023). However, there are detailed morphological differences between S. malongensis sp. nov. and the other two species of Sidneyia . Comparing to the other two species of Sidneyia , S. malongensis sp. nov. has fewer thoracic tergites. Sidneyia malongensis sp. nov. and S. inexpectans share approximately equal pleural angles along the body, but the pleural angles of S. minor become more acute after the seventh thoracic tergite ( Bruton 1981; Stein 2013;

→

Zacaï et al. 2015; Du et al. 2023). The numbers of abdominal segments vary among Sidneyia species. The abdomen of S. malongensis sp. nov. has two cylindrical segments, the abdomen of S. inexpectans consists of three segments, and that of S. minor only bears one segment ( Bruton 1981; Du et al. 2023). The morphology of tail fluke in S. malongensis sp. nov. is more similar to that of S. inexpectans , which has a central telson of similar length to the flanked flaps ( Bruton 1981). By comparison, the tail fluke of S. minor has a notch between the two flanked flaps formed by the shorter central telson ( Du et al. 2023).

The four species of Sidneyia show differences in size and numbers of thoracic tergites and abdominal segments ( Table 3). The body sizes of the lower Cambrian Series 2 S. malongensis sp. nov. and S. minor are smaller than that of the middle Cambrian Miaolingian S. inexpectans and S. cf. inexpectans . Sidneyia malongensis sp. nov. has the least thoracic tergites among the genus. It also has two abdominal segments, Sidneyia minor has one, while S. inexpectans has two or three. The remarkable difference in abdominal length-width ratio also distinguishes these species. The abdominal length-width ratio of S. malongensis sp. nov. is roughly 1, those of S. inexpectans and S. cf. inexpectans are significantly larger (1.20–1.38), while that of S. minor is smaller (0.67).

Stratigraphic and geographic range.— Type locality and horizon only.