Cricocosmia jinningensis Hou and Sun, 2003

Han, Jian, Liu, Jianni, Zhang, Zhifei, Zhang, Xingliang & Shu, Degan, 2007, Trunk ornament on the palaeoscolecid worms Cricocosmia and Tabelliscolex from the Early Cambrian Chengjiang deposits of China, Acta Palaeontologica Polonica 52 (2), pp. 423-431 : 425-426

Cricocosmia jinningensis Hou and Sun, 2003

Figs. 1A–E , 2 , 3 .

Emended diagnosis.—Elongate trunk bears approximately 110 annuli that decrease in wide backwardly and usually form two sub−annuli on the dorsal side. Correspondingly, cone−shaped macrosclerites decrease in size and increase in height. Trunk with or without ventral spines.

Description.—The proboscis of Cricocosmia dictates the anterior/posterior orientation of this animal while the bilateral asymmetry is defined by the paired sclerites and the comparably smooth area between the two rows of lateral sclerites which consisting with the orientation of the terminal hooks, indicate the ventral side of the trunk.

Ventral spines: Approximately 5% of Cricocosmia specimens in our huge collections show two roughly longitudinal rows of tiny spines at the ventral side of the trunk ( Fig. 1A, B ). The arrangement of these spines is not regular, but usually, one annulus bears one or two such spines ( Fig. 1A, B ). The specimens described here do not show any other differences from those devoid of ventral spines.

Lateral sclerites: The presence on the trunk of Cricocosmia of a pair of cone−shaped sclerites on each annulus is well known ( Hou and Bergström 1994). Despite of the first pair of sclerites that are smaller than the second one, the lateral sclerites increase gradually in height and decrease in diameter toward the trunk end; those on the anterior part of the trunk appear to be dorso−ventrally extended elliptical inwardly−curved plates; on the middle part they are shaped as round plates each with a low−relief cone pointing backward; and the posterior sclerites are formed into curved backwardly−pointing sharp spines with a ground base ( Fig. 1A ). Each lateral sclerite has a marginal ridge that is wide and apparent at its part posterior ( Fig. 1E ).

SEM−BSE analysis reveals that the well−preserved lateral sclerites including the marginal ridges consist of a crudely diagonal meshwork of hemi−spherical tubercles or round concave pits ( Figs. 1C–E , 2A–C ). The surface with holes represents the inner side of the epicuticle whereas that with tubercles represents the outer side. In ELI−0001402 and ELI−0001404, the pits in the meshwork range from ca. 2 to 10 ̊m in diameter, and they apparently decrease in size towards the tip of the lateral sclerites ( Fig. 2A 2 –A 4 , C). The skeleton frame separating the pits is also ca. 2–10 ̊m in thickness. In ELI−0001403, the tubercles, which are located on the sclerites near the trunk end, seem to be uniform in diameter. However, the distal part does not show any microstructure probably due to poor preservation. The pits at the edge of the sclerites are complete or an incomplete pit ( Fig. 2A 3 ). Apparently, the sclerites on the posterior trunk are composed of less tubercles than the anterior ones ( Figs. 1C–E , 2A–C ). The thickness of the lateral sclerites is hard to estimate; possibly it is less than the diameter of the pits, ca. 10 ̊m.

SEM reveals that the sclerites in ELI−0001402 consist of densely packed finely spiculate minerals crystals less than 2 ̊m in length whereas the surrounding trunk surface is covered with iron oxide octahedral pseudomorphs of pyrite, which have been replaced by the spiculate mineral crystals ( Fig. 2A 4 , A 5 ). EDX and element mapping reveal that the lateral sclerites are composed mainly of iron oxide with fewer amounts of phosphorus, and the surrounding area is mainly composed of aluminosilicates, probably chlorite ( Fig. 3 ), thus, the spiculate probably are limonite. It should be noted that up to 3.53 wt% of organic carbon and lesser amounts of phosphorus and sulphur can be detected from the mapping area ( Table 1). EDX analysis in ELI−0001403 and ELI−0001404 shows similar results to ELI−0001402.

Figures

Fig. 1. Early Cambrian palaeoscolecid worms from the Early Cambrian Chengjiang deposits, China. A–E. Cricocosmia jinningensis Hou and Sun, 1988. A. ELI−0001400, showing the ventral trunk spines (arrow) of Cricocosmia. B. ELI−0001401, showing the ventral trunk spines (arrow); B2 is the rectangle area on B1. C. ELI−0001402; C1, a complete specimen; C2, lateral spines at the anterior portion of the trunk (rectangle area in C1) preserved fine structure; C3, showing the preserved microstructure of the lateral spines, note that sclerites colored black can preserve finer structure than those of yellow, and that sclerites showing finer structures are apparently dislocated probably due to molting. D. ELI−0001403; D1, a complete specimen; D2, posterior portion of the body (rectangle area in D1) with several spines (arrows pointed) bearing fine structures. E. ELI−0001404; E1, a fragmental specimen in burrowing; E2, showing the trunk sclerites (arrows pointed) with a net−like structure; the marginal ridges are evident on these sclerites. F. Tabelliscolex hexagonus Han, Zhang, and Shu, 2003a, ELI−0001218, holotype, showing the general outline. G. Tabelliscolex maanshanensis sp. nov., ELI−0001219, showing molted trunk sclerites.

Fig. 2. Diagrammatic presentation of the trunk ornamentation in Cricocosmia jinningensis Hou and Sun, 2003 from the Earlyn Cambrian Chengjiang deposits, China. A. ELI−0001402, lateral spines from the anterior trunk (rectangle area in Fig. 1C); A1, one of the plate−shape sclerites with a net structure; the anterior part of the sclerites is broken; A2, one of the cone−shaped sclerites with net−like structure; note the size of the circlet decreases distally; A3, showing the net−like structure; A4, the net−like structure consists of numerous finer spiculate minerals; A5, trunk cuticle surrounding the sclerite consists of bright larger octahedral pyrites, which are also composed of nu− merous micro−spiculate minerals. B. ELI−0001403, lateral spines from the posterior trunk; B1, the lateral sclerites showing a bright white high−contrast colour with surrounding trunk cuticle (rectangle area in Fig. 1D); B2, a lateral spine consisting of many tubercles; B3, showing the tubercles. C. ELI−0001404, showing the lateral sclerites with tubercles.

Fig. 3. Element maps of Cricocosmia jinningensis Hou and Sun, 1988 from the Early Cambrian of Chengjiang, China show that the lateral sclerites of Cricocosmia have elevated content of oxygen and ferrum and depleted sili− con and aluminium compared with other areas of the trunk. A small amount of phosphorus is present on the surface of the trunk, possibly indicating the presence of apatite. The first image is of the anterior cone−shaped sclerites shown in Fig. 2A2, ELI−0001402.

Fig. 4. SEM−BSE images of uncoated specimens of Tabelliscolex from the Early Cambrian of Chengjiang, China. A. Tabelliscolex maanshanensis sp. nov., ELI−0001219, holotype; A1, molted elongate sclerites; A2, shows the tubercles and the pits on the inner side; A3, showing each pit has a inner circlet of concentric laminae; A4, close−up showing the pit and the inner lamina. B. Tabelliscolex hexagonus Han, Zhang, and Shu, 2003a, ELI−0001218, holotype; B1, two over−lapping plates, one plate showing the tubercles (B2) and another showing the pits (B3); B4, the skeleton of the plate, noting the framboidal pyrites within the skeleton; B5, close−up showing framboidal pyrites replicated by finer minerals (B6); B7, close−up of the pit; B8, some needle−like minerals within the pit in B7.

Fig. 5. Element maps of Tabelliscolex maanshanensis sp. nov. from the Early Cambrian Chengjiang deposits, China. Mapping area is the upper right part in Fig. 4A1, ELI−0001219. Images show that lateral sclerites of Tabelliscolex maanshanensis are composed predominantly of silicon, oxygen, and aluminum, with lesser amounts of iron, potassium, and magnesium.