Data from: A new tetraradial olivooid (Medusozoa) from the Lower Cambrian (Stage 2) Yanjiahe Formation, South China

Octapyrgites elongatus n. gen. n. sp., a relatively rare, tetraradial
olivooid (Cnidaria, Medusozoa), is described from Bed 5 of the Yanjiahe
Formation (Cambrian Stage 2) near Yichang, China. Though similar to
Olivooides and Quadrapyrgites from the Fortunian Stage in consisting of a
partially corrugated (long.) periderm with a quadrate (transv.) apical
portion and V-shaped apertural lobes, O. elongatus is substantially larger
than other olivooids. The elongate apical region of O. elongatus is
similar to four-sided Anaconularia anomala, though with a flat tip that
may have been an adaption for a sessile mode of life. As in other
olivooids, embryonic development in O. elongatus may have been direct.
Lastly, the paucity of olivooids and the absence of pentaradial cnidarians
and carinachitids in Cambrian Stage 2 indicate a marked decline in the
disparity of cnidarians near the Fortunian/Cambrian Age 2 boundary, when
by contrast bilaterians underwent rapid diversification.