Some fun weirdness in the tangled “tree of life.” Donald Williamson, a marine biologist who wondered why very different larval forms pop up willy-nilly in very different species, has a bold hypothesis. Although his explanation is very heterodox (though it received serious support from Lynn Margulis) and is yet to be supported by any molecular data, what is much more fascinating is the extent of the problem his theory aims to solve, including the following oddities:
- Very similar larval forms appear in phyla with dissimilar adult body plans.
- Wholly different larval forms appear in the same phylum
- Some echinoderms are develop as protostomes, some as deuterostomes.
- Some mollusks, annelids, sipunculids, and even some deuterostomes have rotifer-like trochophore larvae.