Tabelliscolex chengjiangensis, Han & Liu & Zhang & Zhang & Shu, 2007

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 : 426-427

Tabelliscolex chengjiangensis sp. nov.

Figs. 1G , 4A .

Derivation of the name: After the type locality.

Holotype: ELI−0001219, part and counterpart.

Type locality: Ma'anshan section, Changing County, Yunnan Province, China.

Type horizon: ( Eoredlichia –Wutingaspis Zone) Yu’anshan Member, Heilinpu Formation, Early Cambrian.

Material.— Holotype only.

Diagnosis.—Elongate trunk with annuli that bear a pair of elongate elliptic macroplates on each, constructed by hexagonally arranged tubercles. It differs from Tabelliscolex hexagonus by having a concentric lamina in each tubercle and possibly lacking a dorsal sclerite on each annulus.

Description.—The holotype, ELI−0001219, is completely composed of more than 76 pairs of long elliptical sclerites. All these sclerites are constructed from hexagonally arranged hemi−spherical tubercles (pits) ( Fig. 4A 1 , A 2 ) same with that of Tabelliscolex hexagonus (see Figs. 1F , 4B 1 –B 3 ; see also Han et al. 2003a: pl. 1; Huang 2005: figs. 44–46), thus each sclerite usually has six others surrounding it while the marginal ones have four others. These tubercles are ca. 30 ̊m and the inner surface of the sclerites has an additionally inner circlet within the pit ( Fig. 4A 3 , A 4 ).

SEM analysis of Tabelliscolex hexagonus reveals that the plates are mainly preserved as irregularly shaped argillaceous mineral crystals ( Fig. 4B 4 ) and microspherules that further consist of short plate−like mineral crystals ( Fig. 4B 5 , B 6 ). Some needle−like minerals are present within the pit of a plate ( Fig. 4B 7, B 8). This is also the case for Tabelliscolex chengjiangensis sp. nov. EDX and element mapping shows that the plates of Tabelliscolex chengjiangensis sp. nov. are mainly composed of oxygen, aluminum, and silicon, representing aluminosilicates, with a lesser amount of iron representing iron oxide, and phosphorus and calcium representing apatite phosphate, as well as organic carbon (6%) that can be found in the mapping area ( Fig. 5 ; Table 2). The plates could not be distinguished from the surrounding trunk in the element mapping, but it did reveal that the fossil is composed mainly of oxygen, aluminum, silicon, components of the aluminosilicates.

Discussion.— Tabelliscolex hexagonus was described as bearing two sets of trunk sclerites, one row of elliptic plates on the dorsal side and two lateral rows of elongate elliptical plates, so that each annulus has three sclerites ( Han et al. 2003a). The holotype specimen of T. chengjiangensis sp. nov. does not preserve the equivalent dorsal sclerites of T. hexagonus ; thus, such structure need more specimens to be confirmed.

It seems unlikely that the concentric laminae in T. chengjiangensis sp. nov. are artefacts of preservation; they are also not newly secreted cuticle replacing older ones because the holotype specimen had already been molted.

Stratigraphic and geographic range.— Type locality only.

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. 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. 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. 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.

Fig. 6. Reconstructions of the palaeoscolecid worms Cricicosmia and Tabelliscolex (modified from Huang 2005b). A. Cricocosmia jinningensis; A1, whole animal; A2, typical lateral sclerite of Cricocosmia jinningensis. B. Tabelliscolex hexagonus. C. Tabelliscolex maanshanensis sp. nov.