Peel—Problematic Cambrian cnidarian (Octocorallia?) The basal surface of several internal molds is flattened
(Figs. 3.7–3.9, 3.11, 4.5), possibly representing a broadening of the area of attachment (Fig. 3.5), the presence of a transverse tabula within the corallum (as seen in the type species, Fig. 1.1), or a basal plug of shell material. The mold surface carries eight radiating rounded ridges, comparable to those seen in the holotype (Fig. 3.3), but secondary ridges are quickly inter- spersed between the primary eight (Fig. 4.5, 4.6). Thus, 16 grooves (four of which are arrowed in Fig. 3.7) crossed by pore- infillings on the internal mold correspond to 16 pore-traversed septa on the corallum interior. In one specimen, viewed from the base (Fig. 4.1–4.3), the
attachment surface is broken away; it is 1.2mm in diameter. A circular inner zone (Fig. 4.3), forming half the specimen diameter, is surrounded by an irregular network of infilled pores (Fig. 4.1–4.4) that represent two growth iterations (Fig. 4.2). The inner zone displays eight equidistant tubes, each of which represents a now-dissolved solid structure ~80 µmin diameter, but crossed by infrequent pores. The tubes slope radially outwards in this basal view, with steep inclination, as indicated by the impression of their inner margin on the central area, forming a similar pattern to that seen on the basal termination in Figure 4.5. Fine pores ~10 µm in diameter are concentrated in the central part of the inner zone and along the eight radiating ridges between the eight tubes (Fig. 4.3). The pore arrangement in the outer zone is labyrinthine; pores are interconnected, but they are irregular in shape, orientation and diameter, the latter varying from ~5 µmto30 µm (Fig. 4.4). There is a tendency for individual pores to swell at junctions with other pores. Budding from the corallum has not been observed, but
several specimens show rejuvenescence of the corallum (Fig. 3.2). Several internal molds lack septal grooves in their earliest growth stage (Fig. 3.6).
Etymology.—From koori (Greenlandic), basket.
Remarks.—Variation in the morphology of the preserved internal molds of Cambroctoconus koori n. sp. suggests that phosphatization was not a uniform process. While some specimens show a high degree of penetration of the porous wall of the corallum and detailed moldic reproduction (Fig. 4.1–4.4), others show more massive textures suggesting simple or even repeated molding of the calice or a lack of penetration of the pore complex (Fig. 3.5). The differences may also reflect pre- or postmortem closure of pore spaces by carbonate. With a total preserved height of 3mm, internal molds
of C. koori n. sp. are much smaller than the type species C. orientalis (height 11–13mm; Park et al., 2011), C. coreanensis (height 11–16mm; Park et al., 2016), or C. kyrgyzstanicus (height 7mm; Peel in Geyer et al., 2014). However, the extent of phosphatization within coralla of C. koori n. sp. is not well known in most specimens, and it is probable that phosphatization was restricted often just to the deepest portions of the calice. Thus, the original calcareous coralla of many specimens of C. koori n. sp. may have been higher than the preserved internal molds. Several specimens lack indications of septa on the outer wall of the corallum and this surface, as preserved, may
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approximate to the true outer wall of the corallum (Figs. 3.10, 4.10, 4.11). Thus, phosphatization has replaced the entire specimen rather than just forming a mold of the interior. In the largest available specimen (Fig. 3.10), the turbinate earliest growth stage is octagonal in cross-section (not a common feature in C. koori n. sp.) and is succeeded, following a clear transverse fracture, by a cylindrical latest growth stage, which is interpreted as the outer surface of the corallum. The floor of the calice is preserved in several of the specimens that lack indications of septa on the outer corallum wall (Fig. 4.10, 4.11). Radiating and bifurcating ridges (Fig. 4.11, point of bifurcation arrowed) can be equated with the bifurcating septal grooves in other specimens (Fig. 3.1, arrows). However, deep septal grooves in the outer surface (Fig. 3.6) correspond to ridges on the calice interior (Fig. 3.13), clearly demonstrating that the entire specimen is an internal mold of the calice. Apart from greater size, C. orientalis and C. kyrgyzstanicus
fig.1) show budding from the calice brim and from the corallum walls, with stacks of successively formed corallites. Several daughter corallites may arise from a single parent, but connection between polyps through the walls is not seen. Budding from the corallum walls is not known in C. koori n. sp., but rejuvenation is seen (Fig. 3.2), as illustrated also by Park et al. (2011, fig.1i, 1k, 1l) in the type species. Park et al. (2011, supplementary figs. S4, S5) illustrated large numbers of closely juxtaposed specimens ofC. orientalis on a bedding plane, which were interpreted as forming a colony. It is not known if these specimens represent just a physical association of individuals, either in life or death, or formed a colony of biologically connected individuals. Park et al. (2011) referred to the associations as colonies, but their comment that the lack of shared colonial tissue (coenenchyme) was a point of difference with Anthozoa suggests just association rather than connection of individuals. Cambroctoconus coreanensis, from the Daegi Formation
differ from C. koori n. sp. in the much more strongly expressed octagonal cross-section of their coralla. An octagonal form has been observed only rarely in specimens from Greenland (Fig. 3.10) where the majority have a circular cross-section. To some extent, this may reflect a difference in calcification between the outer wall of the corallum and the calice, but thin-sections illustrated by Park et al. (2011, fig. 2) indicate that the octagonal form of C. orientalis is maintained within the calice. Apart from the difference in cross-section, both C. orientalis and C. koori n. sp. show a similar range in the overall shape of the corallum. Specimens of C. orientalis illustrated by Park et al. (2011,
(Cambrian Series 3, Drumian) of Korea (Park et al., 2016), differs from C. koori n. sp. in its slender, slightly sinuous coralla, but its internal structures are not well known.
Eight-fold symmetry of Cambroctoconus
The eight-fold symmetry in Cambroctoconus orientalis, expressed by the octagonal corallum and eight pairs of septa, is a characteristic feature of octocorals and staurozoans, but it is not confined to cnidarians. It is also characteristic of ctenophores, which were already well represented in the Cambrian (Conway Morris and Collins, 1996; Hou et al., 2004; Ou et al., 2015).
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