The Cambroernida are a clade of Paleozoic animals with coiled bodies and filamentous tentacles. They include a number of early to middle Paleozoic (Cambrian to Devonian)
Description
Cambroernids encompass three particular types of enigmatic animals first appearing in the Cambrian:
Herpetogaster (the
type genus),
Phlogites, and the
Eldonioidea. They are united by a set of common features including at least one pair of bifurcated or divided oral tentacles, and a large stomach and narrower intestine enclosed together in a clockwise-coiled sac.
Taxonomy and evolution
Body coiling increased throughout this group's evolution.
has a segmented and clockwise-curved body attached to the substrate via a narrow and partially mobile
stolon (stalk).
Phlogites was even more simple, with a thick immobile stolon leading up to a tentacle-bearing calyx (cup-shaped main body), with internal gut coiling. The eldoniids
(also known as eldonioids
or eldonids
) were diverse and disc-shaped, commonly described as "medusiform", i.e.
jellyfish-shaped. Though the lifestyle of eldoniids is still debated, it can be agreed that they had a large curved stomach and no stolon.
The lack of a post-anal tail in cambroernids suggests that, contrary to long-held assumptions, this feature was not present in the common ancestor of deuterostomes. This is congruent with the significant differences between the post-anal tails of chordates and hemichordates. This and other features of cambroernids suggest that post-anal tails, gill bars, and a U-shaped gut evolved multiple times in the deuterostomes through convergence.
Segmentation, as seen in Herpetogaster, is a notable characteristic of chordates not seen in other ambulacrarians, indicating that it might be a trait of ancestral deuterostomes.
Phylogeny
Phylogenetic analysis offers strong support for Cambroernida as a clade of stem-group ambulacrarians.
The following cladogram is simplified from Li
et al. 2023; only a sampling of eldonioids were included in the analysis:
Internal classification
Genera whose family placement is tentative are preceded with (?).
Note that some authors continue to treat Stellostomites as a separate taxon.
History of identification
Previously, some cambroernids were compared to members of the broad invertebrate clade
Lophotrochozoa. In particular, they were allied with the
Lophophore, a subset of lophotrochozoans bearing a crown of
Cilium tentacles known as the
lophophore.
[ ] However, this interpretation has more recently been considered unlikely, insofar as cambroernids are interpreted as
, whereas lophophorates are
.
Works cited
