Onychodictyon ferox Hou, Ramsköld, and Bergström, 1991

Liu, Jianni, Shu, Degan, Han, Jian, Zhang, Zhifei & Zhang, Xingliang, 2008, The lobopod Onychodictyon from the Lower Cambrian Chengjiang Lagerstätte revisited, Acta Palaeontologica Polonica 53 (2), pp. 285-292 : 286

Onychodictyon ferox Hou, Ramsköld, and Bergström, 1991

Material.— All specimens came from a grayish−green and grayish−yellow mudstone from the Jianshan section in Haikou village, Haikou County, and the Erjie section in Erjie village , Anning County , Kunming , Yunnan. Helinpu (Chiungchussu) Formation , Yu’anshan Member ( Eoredlichia Zone ), Lower Cambrian .

Diagnosis.—Robustly built lobopod, the body comprises a rounded “head” with “antennae”, the trunk with 10 segments and 11 pairs of limbs, long papillae on body and limbs, 10 pairs of plates on the dorsal of the body.

Description.—One complete adult specimen of Onychodictyon ferox is about 50–70 mm long (Fig. 1A 1 –A 3). It possesses a small head region, which is semi−round in shape. In specimen ELIJSO−013, the “head” is a little convex dorsally, with a semi−elliptical profile and a maximum sagittal length of 2 mm, approximately 50% of its width (Fig. 1A 1 –A 5). A pair of flagellum−like structures is about 4 mm long and 0.5 mm wide, protruding from the dorso−lateral side of the “head”; compared with the trunk limbs, the flagellum−like structures are thin and gentle with no annuli or nodes. Therefore, they are most likely sensory appendages (“antennae”) (Fig. 1A 1 –A 5). Similar appendages also occur in dorsolaterally preserved specimen ELIMF−015B ( Fig. 3D). No eyes and head shield are preserved.

The worm−like trunk region is sub−rounded in cross−section. It is composed of 10 segments, with a number of strong and clear annuli (Figs. 1A 1 –A 5 and 3C 1, C 2). The anterior portion of the trunk in front of the 3 rd segment comprises 2–3 annuli, the 4 th, 5 th, 6 th, and 7 th segments of the trunk possesses 5–6 further annuli, the posterior portion of the trunk behind the 7 th segment bears 3 annuli (Fig. 1A 1, A 2). Each annulus has a vertical row of “tubercles”; there are usually 10 tubercles in one row observed around the circumference (Fig. 1A 1, A 2). Long, finely annulated appendicules extend from these “tubercles”. In each annulus, the appendicules are symmetrically placed relative to the dorsal midline. As in the trunk limbs, fine canals can be observed in these protrusions (Fig. 1B 1, B 2).

Ten pairs of plates are located dorsally in turn in the 10 segments. Each plate is sub−rounded, shows three−dimensional structures (convexity, ridges, rims), with a central broad−based spine directed obliquely upward and out (Figs. 1A 1 –A 3, B 1 and 2B).

There are 11 pairs of limbs, the anterior 10 attach at a circular area beneath each plate, the last pair located at the end of the trunk (Fig. 1B 1). The limbs are cylindrical, protruding ventro−laterally from the trunk, all possessing thin, transverse annuli, about 30 in number from the base to the tip (Fig. 1A 1, A 2, B 2). Each limb carries along its length at least two rows of tubercles, similar to those of the trunk (Fig. 1A 1, A 2, B 2). The number of tubercles in each row is at least 10, probably up to 20, and small appendicules can be observed protruding from these tubercles, as in specimen ELIJSO−002A ( Fig. 2C), Compared to those of the trunk, the appendicules of the limbs are shorter and thinner. A pair of claws occurs at the end of each limb ( Fig. 3E), the direction of each claw varies depending on the preservation of the specimens, except for the claws of limb 11, where the direction is usually bent anteriorly (Fig. 1B 1). The posture further underlines the adaptation of the posterior limb pair to an anchoring function, as suggested by Chen et al. (1995) and Ramsköld and Chen (1998).

The gut is straight and simple (Fig. 1A 1 –A 3), usually preserved in a flattened black band, which lies near the ventral margin. No anus has been found.