Other Possible Skeletal Cnidarians

Among Cambrian small shelly fossils, a number of tiny, often septate, conoidal tubes have been suggested to be of cnidarian affinity, namely, paiutiids, quadriradial cari-nachitiids and hexangulaconulariids, triradial anabaritids, and byroniids (for reviews, see Conway Morris and Chen 1989, 1992; Bengtson et al. 1990; Rozanov and Zhuravlev 1992). Except forbyroniids, these animals are restricted to the Early Cambrian. Most of them are suggested to be sessile forms. Tentacle-bearing Cambrorhytium might be a cnidarian possessing an organic-walled tube (Conway Morris and Robison 1988). It is worth noting that phosphatized spheroids, in Nemakit-Daldynian strata containing anabaritids, resemble nonplanktotrophic cnidarian actinula larvae (Kouchinsky etal. 1999).

Figure 14.7 Distribution of sponges and cnidarians in relation to salinity (A), in relation to depth (B), and in relation to time (C).

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