Dinomischidae Conway Morris 1977

Family Dinomischidae Conway Morris, 1977 Amended diagnosis (amended after Conway Morris, 1977, p. 834). Polypoid, sessile organism bearing a calyx encircled by tentacle-sheath complexes, with an organic skeleton. The basal portion of the calyx varies from a circular pit to a slender stalk. The tentacle carries sets of pinnules, each with a row of cilia, and preserves a set of paired dark stains. The outer sheath flanking each tentacle present. Remarks. Only one genus, Dinomischus, was assigned to the family Dinomischidae in previous studies (Chen et al., 1989; Conway Morris 1977; Peng et al., 2006), and although the genus Siphusauctum was considered closely related to Dinomischus, a separate family, Siphusauctidae, was erected for it (O'Brien & Caron, 2012). Dinomischus has long been interpreted as an entoproct comprising a calyx and sclerotized bracts (Chen et al., 1989; Conway Morris, 1977). A recent study revealed a potential blind digestive tract and a partitioned cavity in some well-preserved Dinomischus specimens, indicating that it is less likely to be a bilaterian entoproct which possesses a typical U-shaped gut (Zhao et al., 2019). Paired dark stains and pinnules identified recently in the bract of Dinomischus are similar to that of Daihua, and the body plan of Dinomischus has thus been revised as comprising a calyx and pinnate, sclerotized tentacles (Zhao et al., 2019). The present study further reveals that similar dark stains, as well as ciliated pinnules, appear in the longsword-shaped tentacles of Xianguangia. The tentacle in Siphusauctum also bears paired sets of dark stains, but lacks pinnules and is non-sclerotized. The outer sheath surrounding each tentacle has been identified in Xianguangia, Daihua, Dinomischus and Siphusauctum as well, but it likely varies in number. It is reasonable to formally assign the genera Xianguangia and Daihua, together with Dinomischus, to the family Dinomischidae, a monophyletic group recovered in our Bayesian phylogenetic analyses. The 18 pinnate, sclerotized tentacles, plus a calyx with an organic skeleton, could be recognized as synapomorphies for this family. Although our phylogenetic results support the previous hypothesis that dinomischiids are a total-group ctenophore (Klug et al., 2021; Zhao et al., 2019), alternative phylogenetic analyses with different scores on the characters ‘cushion rows’ and ‘large cilia’ recover dinomischiids as either a stem-group ctenophore or in a polytomy with ctenophores and cnidarians. The phylum-level affinity of dinomischiids is indeterminate, and new fossil taxa with anatomical transformations would provide critical information to verify its position in the tree of life. Genera included. Dinomischus Conway Morris, 1977; Xianguangia Chen & Erdtmann, 1991; Daihua Zhao et al., 2019. Occurrence. Cambrian unnamed Series 2, Stage 3, Chengjiang biota, South China (Xianguangia, Daihua, Dinomischus); Miaolingian Series, Wuliuan Stage, Burgess Shale, Canada, and Kaili biota, South China (Dinomischus); Miaolingian Series, Barrandian area, Czech Republic (cp. Dinomischus).

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