Soft Bodied Cnidaria and Ctenophores

In contrast with the Precambrian Ediacara fauna, which is dominated by medusoids, representatives of the soft-bodied cnidaria and ctenophores are relatively poorly represented in the Cambrian. A great number of Cambrian forms have been assigned to Cnidaria with varying degrees of uncertainty. Impressions of putative jellyfish have been reported in Cambrian rocks since Walcott (1911), but most of them have been reinterpreted as trace fossils, sponges, echinoderms, arthropod appendages, or worms; others have been designated as incertae sedis or are unrecognizable forms (Harrington and Moore 1956; Conway Morris 1993a). The discovery of annulated disks alone is insufficient to place them in the chondrophores. The Tommotian records are still doubtful. Associated with Lapworthella, 50 m above the Cadomian peneplain, forms provisionally attributed to scyphozoans have been recorded (Doré 1985) (figure 14.5B).

Other discoidal fossils have been described in Europe but have not recently been reinvestigated, so their possible attribution to cnidarians remains uncertain. Ichnusina cocozzai (nom. correct. herein) (figure 14.5A)—from Sardinia, Italy, at the base of the "Arenarie di San Vito" (Middle-Upper Cambrian)—is one of these. It consists of a hemispheric body with undifferentiated center, dichotomized radial lobes and peripheral tentacles. If considered as a possible cnidarian, then this organism would have had a swimming or floating lifestyle.

Within the Middle Cambrian Burgess Shale-type fauna, some specimens resembling elements of the Ediacara fauna have a cnidarian affinity (Conway Morris 1993b). Thaumaptilon is a bilaterally symmetrical foliate animal with a holdfast and is related to pennatulaceans. It was benthic, and its mode of feeding rather conjectural, probably trapping the food particles by means of small tentacles of putative zooids. Ge-

Figure 14.5 A, Disk of a possible chondro-phore cast of Ichnusina cocozzai (Debrenne), MNHN M84160, Middle-Upper Cambrian (Sardinia, Italy). B, Cubic medusoid with square central part (gastrogenital cavity?), with a tentacle springing from the lower right angle

of the manubrium (?), surrounded by a dark organic circle (umbrella?), N 1368A Caen University, Lower Cambrian "Schistes et calcaires" Formation (Normandy, Val de May, Normandy, France). Source: Photograph courtesy of Francis Doré.

lenoptron is tentatively assigned to chondrophorines (Conway Morris 1993b), together with some undetermined disks with spaced annulations and tentacles. Emmonsaspis from the Early Cambrian Parker Slate of the Appalachians is tentatively interpreted as a benthic suspension feeder or microcarnivore (Conway Morris 1993b).

The trace fossil Dolopichnus is interpreted as a possible cnidarian burrow (Alpert and Moore 1975; Birkenmajer 1977). It contains trilobite debris, indicating a carniv orous diet. Such trace fossils might be produced by animals similar to the Early Cambrian Xianguangia or Middle Cambrian Mackenzia. Xianguangia from Chengjiang is interpreted as an anthozoan-like cnidarian on account of a basal disk, a polyp-like body with possible septal impressions, and a distal crown of tentacles bearing closely spaced pinnules (Chen and Erdtmann 1991). Mackenzia costalis Walcott, having a baglike body with possible internal partitions, is compared with some putative ac-tinians (Conway Morris 1993b).

Ctenophores, representatives of another branch of the coelenteratan grade, were active swimmers that combed the pelagic realm in search of tiny metazoans and larvae (Conway Morris and Collins 1996; Chen and Zhou 1997).

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