Li et al.—Yuyuanozoon magnificissimi from the early Cambrian Chengjiang Biota 92(6):1081–1091


summarized in Figures 1 and 2, which also denote how terms such as ‘ventral’ and ‘dorsal’ are applied to vetulicolians.


Preservation and taphonomy


Specimen YKLP 13071 (Fig. 3) is, like most vetulicolians, lat- erally compressed and retains some three-dimensional (3-D)


relief. The majority of the anterior section is preserved as a thin film that does not appear to have been biomineralized though the areas adjacent to the anterior opening and the posterior end show patches of dark color. The texture and composition of this material is identical to the iron oxide coatings typical in Chengjiang fossils (Gabbott et al., 2004; Forchielli et al., 2014) and is not consistent with in vivo mineralization. The anterior section appears to comprise six subdivisions that are demarcated by five lines that circumvent the entire structure and are coin- cident with the five lateral cowl-shaped pouches. At the mid- point between the boundaries of these subdivisions on the dorsal side a shorter parallel line occurs, which was termed second- order annulation by Aldridge et al. (2007). There are clear wrinkles along the ventral side of the anterior section, which appear to suggest an element of twisting and/or compression postmortem. The boundary between anterior subdivisions five and six


also coincides with a marked change in relief, with the sediment fill within the anterior section thicker anteriorly and the color


darker posteriorly. The posterior section of the holotype (CFM00059)


possesses seven segments; within each segment there are five, or possibly six, less well-defined lines that appear to circumvent the whole structure and thus resemble annulation. Other speci- mens, which are incomplete, preserve five (YKLP 13071) or six (YKLP 13070) posterior segments.


Systematic paleontology Class Vetulicolida Chen and Zhou, 1997


Order Vetulicolata Hou and Berström, 1997 Family Didazoonidae Shu and Han in Shu et al., 2001


Type Genus.—Didazoon Shu and Han in Shu et al., 2001. Other genera.—Pomatrum Luo and Hu in Luo et al., 1999; Yuyuanozoon Chen, Feng, and Zhu in Chen et al., 2003; Nesonektris García-Bellido et al. 2014.


Diagnosis.—(Modified from Shu et al., 2001, Aldridge et al., 2007) Bilaterally symmetrical animal with clear subdivision of body into presumed anterior and posterior sections. Neither the subquadrate to ovoid anterior section nor the posterior section is biomineralized. The anterior section has a large, circular open- ing at the presumed anterior end of the animal, posterior of which are six subdivisions demarcated by five lines; five, pre- sumed laterally positioned, oval openings on both sides of the anterior section coincide with the lines of subdivision. Segments of posterior section may bear up to six annulations.


Remarks.—In addition to characters listed by Shu et al. (2001), in well-preserved specimens of Yuyuanozoon (herein) and


1085


Figure 2. Additional morphological features for Yuyuanozoon. Abbreviations are as follows (terms used by other authors are in parentheses). Cv=circumventing feature behind the anterior opening (oral disc.); Mr=marginal region at the anterior opening (mouth plate); Ol=ordering lines (putative segments, anterior segments), lines circumventing the anterior section coalescing with lateral pouches and long axis perpendicular to the body axis.


Didazoon (YJL’s personal observations), the posterior section displays annulation within each segment. Morphological features, including the circumventing


feature behind the anterior opening of the anterior section, the posterodorsal (‘fin-like’) prolongations on the anterior section, the shape of the lateral pouches, and the segmented posterior section with annulations, place Yuyuanozoon in the Didazooni- dae rather than in the Vetulicolidae (see also Table 1).


Genus Yuyuanozoon Chen, Feng, and Zhu in Chen et al., 2003


Type species.—Yuyuanozoon magnificissimi Chen, Feng, and Zhu in Chen et al. 2003, by monotypy.


Diagnosis.—(Modified from Chen et al., 2003, Aldridge et al., 2007) Didazoonid with nonbiomineralized, elongate ovoid ante- rior section.Anarrow, raised rim circumvents the entire perimeter of the anterior section, some 5mm posterior of the anterior opening. Marginal projections and lateral groove absent from anterior section. Posterior section has seven segments,within each of which are five to six annulations; terminal segment longest.


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