Phlogites

''Phlogites'' is a member of the extinct ambulacrarian stem group Cambroernida, occupying an intermediate position between the basal '' Herpetogaster'' and the more derived Eldonioidea. It is known from the Lower Cambrian Haikou Chengjiang deposits of China.

Description

Phlogites was a cup-shaped animal with a branching tentacular feeding system leading to a dextrally coiled gut with a lateral anus. Sources differ as to the number of tentacles, with two, three, three or five, or four or five tentacles said to be on the anterior part of the calyx. Smooth semi-circular lobes are present between the tentacles.

Compared to the earlier-diverging cambroernid ''Herpetogaster'', ''Phlogites'' lacked segmentation and had a more massive stolon that is contiguous with the body. The coiling present in the external form of ''Herpetogaster'' became internal, except for a small lobate extension with the anus opening laterally. The tentacles of ''Phlogites'' were also more massive, and seem to have branched dichotomously.

Phylogeny

The following cladogram is simpllified from Li ''et al.'' 2023:

History of interpretation

''Phlogites'' was initially considered to be an early lophophorate. A new phylum, Dendrobrachia (Hou, Bergstrom, Ma and Zhao, 2006) was later proposed to encompass it. While some similarities were noted with the eldonioids (and phoronids), the authors were not sufficiently confident to either group ''Phlogites'' with the phoronids or include the eldonioids in the Dendrobrachia.

Since ICZN precedence rules do not apply at the phylum level, later researchers opted to propose cambroernids as an informal group rather than expanding the phylum Dendrobrachia, noting that "not only is the concept of phyla essentialist but it serves to place problematic taxa in a phylogenetic limbo, rendering them effectively immune to further evolutionary analysis." The informal group "cambroernids" was later given the formal name Cambroernida once further evidence was found to support its monophyly.

The interpretation of ''Phlogites'' has been complicated by its proposed equation (as a senior synonym) with the possible first-discovered Cambrian tunicate ''Cheungkongella ancestralis'' (sometimes misspelt ''Cheungkungella'') by the discoverers of another candidate for the title of the oldest known Cambrian tunicate, ''Shankouclava''.

The discoverers of ''Shankouclava'' agreed with the discovers of ''Phlogites'' that ''Phlogites'' is most likely a lophophorate, although they noted possible affinities with ambulacrarians or with Sipuncula. A different group of researchers agreed with synonymizing ''Cheungkongella'' with ''Phlogites'', but proposed a new phylum, Dendrobrachia, with affinities to the Gnathifera.

Neither group proposed tunicate affinities for ''Phlogites'', but later works by the discoverer of ''Shankouclava'' contain statements such as "although Lower Cambrian ''Phlogites'' (=''Cheungkongella'') was claimed as a tunicate (Shu et al., 2001)" that have led to confusion on this point by associating the tunicate affinity claims that only ever applied to ''Cheungkongella'' with ''Phlogites''.

A researcher who was not part of any of the teams discovering ''Phlogites'', ''Cheungkongella'', or ''Shankouclava'', or proposing Dendrobrachia, examined the fossils and concluded that the similarity between ''Phlogites'' and ''Cheungkongella'' was "superficial." The question of whether ''Cheungkongella'' is a synonym of ''Phlogites'' remains unresolved, but does not impact the current theory of ''Phlogites'' as a cambroernid.

References

Works cited

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Cambroernids
Cambrian animals
Cambrian animals of Asia
Prehistoric bilaterian genera
Fossil taxa described in 1999
Cambrian genus extinctions
Monotypic prehistoric animal genera

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