The fossil record shows a “Hexapod Gap.” Unfortunately for Darwin, the two leading theories to explain the gap can be ruled out.
Sponges are outliers in biology’s big bang, the Cambrian explosion. Their embryos appear in Precambrian strata, leading some to consider them primitive.
It’s interesting to see what Derek E. G. Briggs is willing to admit about the Cambrian explosion.
Whenever you find papers and articles dealing with the Cambrian fossil record in the usual science journals, there are commonalities.
Such accounts invoke the abrupt appearance of key features of advanced eyes including the lens, cornea, and iris.