The early Cambrian fossil embryo Pseudooides is a direct-developing cnidarian, not an early ecdysozoan.

The early Cambrian fossil embryo Pseudooides is a direct-developing cnidarian, not an early ecdysozoan.
Proc Biol Sci. 2017 Dec 20;284(1869):
Authors: Duan B, Dong XP, Porras L, Vargas K, Cunningham JA, Donoghue PCJ
Abstract
Early Cambrian Pseudooides prima has been described from embryonic and post-embryonic stages of development, exhibiting long germ-band development. There has been some debate about the pattern of segmentation, but this interpretation, as among the earliest records of ecdysozoans, has been generally accepted. Here, we show that the 'germ band' of P. prima embryos separates along its mid axis during development, with the transverse furrows between the 'somites' unfolding into the polar aperture of the ten-sided theca of Hexaconularia sichuanensis, conventionally interpreted as a scyphozoan cnidarian; co-occurring post-embryonic remains of ecdysozoans are unrelated. We recognize H. sichuanensis as a junior synonym of P. prima as a consequence of identifying these two form-taxa as distinct developmental stages of the same organism. Direct development in P. prima parallels the co-occuring olivooids Olivooides, and Quadrapyrgites and Bayesian phylogenetic analysis of a novel phenotype dataset indicates that, despite differences in their tetra-, penta- and pseudo-hexa-radial symmetry, these hexangulaconulariids comprise a clade of scyphozoan medusozoans, with Arthrochites and conulariids, that all exhibit direct develop...

Source: Biol Sci Space - December 15, 2017 Category: Science Authors: Duan B, Dong XP, Porras L, Vargas K, Cunningham JA, Donoghue PCJ Tags: Proc Biol Sci Source Type: research