Peel—Problematic Cambrian cnidarian (Octocorallia?)


vermiform pore-infillings seen in C. koori n. sp. (Fig. 3.3, 3.4). However, vermiform pores may be developed in many ‘irre- gular’ archaeocyaths, including the rare Cambrian Series 3 (Drumian) representative (Wood et al., 1992), and an inner wall may be lacking (Hill, 1972; Debrenne et al., 2000). While preservational differences hinder comparison between C. koori n. sp. and archaeocyaths in their typical preservation, thin sections of C. orientalis and C. kyrgyzstanicus show a thick outer wall and long septa unlike archaeocyaths (Park et al., 2011; Geyer et al., 2014). Anthaspidellid sponges, such as Fieldospongia Rigby,


1986 and Rankenella Kruse, 1983, may appear superficially similar to the internal molds of Cambroctoconus koori n. sp., but their framework is composed of interlocking spicules rather than a network of pores traversing septa (Kruse and Zhuravlev, 2008; Botting and Peel, 2016; Lee et al., 2016). Pores in archaeocyathans and other sponges are open canals


for the passage of water currents with food particles into the central cavity, a role that is difficult to reconcile with the calical cavity of a supposed cnidarian containing a tentaculate polyp. The coenenchyme of octocorals is penetrated by a complex


series of tubules (solenia), which connect adjacent polyps and distribute nutrients. The coenenchyme is often heavily sup- ported by calcareous spicules, especially around the polyps (Bayer, 1956), but in Epiphaxum the polyps possess a solidly calcified, tubular outer wall with 16 rounded ridges that alternate with u-shaped channels of similar width. However, only half this number is present in a juvenile specimen of Epiphaxum breve Bayer, 1992 (see Bayer, 1992, fig. 14), giving an octoradial form similar to Cambroctoconus. The channels are occupied by solenia, which pass through solenial pores ~30– 40 µm in diameter, but are accompanied by vertical rows of tiny pores (diameter 10 µm). The large pores in the 16 external channels join laterally so that only eight rows of pores are pre- sent internally, alternating with the mesenteries. In a calice of Epiphaxum septifer illustrated by Bayer (1992), the eight internal rows of large pores alternate with radial septa. Solenia occupy galleries 100–200 µm in diameter in the calcified coenenchyme of Nanipora kamurai, where the outer surface of the calcareous polyp tubes is not ridged, as in Epiphaxum, but covered with 5 µm diameter pores, possibly desmocytes anchoring soft tissues to the skeleton (Bayer, 1992). The large solenial pores in the polyp walls of Epiphaxum


are more highly organized than those in Cambroctoconus, which compare more closely in form with the system of solenia within the coenenchyme (Bayer, 1956, fig. 134). However, the perforation of the outer wall of the corallum in Cambroctoconus (Fig. 1.2, 1.4) indicates that the corallum was enveloped by a thin layer of coenenchymal tissue (Fig. 5), as in Nanipora, rather than just an edge zone to the calice, as is the case in solitary rugosan and scleractinian corals. Excellent illustrations of both the aragonite skeleton and the living colony of Nanipora were presented by Miyazaki and Reimer (2015).


Systematic position of Cambroctoconus


Similarity of Cambroctoconus with octocorals, suggested by the octagonal cross-section of the corallum and the eight-fold arrangement of septa, is supported by the interpretation of the


879


pores in the walls of the corallum and septa as solenia within the mesoglea of the coenenchyme (Fig. 5). Thus, the corallum is formed as a cup to the polyp by massive calcification around the solenia that in octocorals distribute nutrients between the individual polyps and the coenenchyme. The calcified corallum can be compared in its place and function with the aragonitic skeletons of present day Epiphaxum and Nanipora, which are also perforated by pores, although these are tubular calices within colonial organisms rather than individual conical coralla. The corallum is also analagous with the fused spicular calcite skeletons developed within the mesoglea that serve to elevate the polyps above the stolon in many extant octocorals (calyx of Bayer, 1956). This spicule-based skeleton is particularly prominent in Tubipora. Coralla of Cambroctoconus achieved stability by cementation to the substrate (Fig. 3.12), but the basal surface in Epiphaxum may be formed by a massive carbonate deposit (Bayer, 1992). There is no preserved record of stolons or other extensions


of coenenchymal tissue beyond the coralla in Cambroctoconus, but if present, it is likely that these were not calcified; they may have been spiculate. However, a particularly dense pattern of solenial pores in the basal area of Cambroctoconus (Fig. 4.1–4.4) may suggest enhanced nutrient flow in this area. The solenial pores of Cambroctoconus served to distribute nutrients from the gastric cavity to the mesogleal layer, pro- viding a base for the significant energy investment involved in the production of the calcified skeleton. However, stolons are also lacking in Taiaroa tauhau Bayer and Muzik, 1976, the only present day solitary octocoral, individuals of which are secured within the sediment by numerous thread-like holdfasts. The lower part of the cylindrical T. tauhau (acanthostele) is sup- ported by eight prominent ridges reinforced with closely packed sclerites. Despite their extensive spiculation (Bayer, 1956),


octocorals have left little trace in the fossil record. Bayer (1992, figs. 9, 10) illustrated incorporation of calcitic spicules into the aragonite polyp walls of Epiphaxum, but such spicules have not been recognized in Cambroctoconus koori n. sp. It is possible that individual coralla of Cambroctoconus


developed periodically from creeping or sheet-like stolons in similar fashion to the simple, upright, polyps of the present day octocoral Clavularia de Blainville, 1830. However, stolons are not present in Taiaroa tauhau, the only living solitary octocoral (Bayer and Muzik, 1976), and evidence of their presence in Cambroctoconus is lacking. Extension of coenenchyme beyond the initial corallum would be a first step to the establishment of the colonial growth characteristic of almost all octocorals. Coralla in Cambroctoconus achieved stability by cementation to the substrate (Fig. 3.12), although the body of T. tauhau is supported by fibrous holdfasts. Budding in Clavularia takes place from the stolons, but daughter zooids in telestacean octocorals are produced directly from the outer coenenchymal wall of the parent, from the anastomosing network of solenia (Bayer, 1973). Park et al. (2011) noted that anthozoan polyps arise from


the mesoglea. Because budding in Cambroctoconus orientalis took place on both the outside and inside of the parent corallum, they argued that the skeletal wall must have been highly inte- grated with the soft tissues from which the daughter coralla arose, although similar budding was also described in


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