I've been reading about the peculiar metamorphosis of the starfish, Luidia sarsi, which eats shellfish and dwells in the muddy sediment of seashores from Norway to the Mediterranean. The diaphanous larva is bilaterally symmetrical; the adult form, with its five arms, is radially symmetrical, a most irregular circumstance. Moreover, the adult emerges from the larva in a different way than the butterfly from the caterpillar, where the structure dissolves and reforms. The starfish develops from a cluster of cells lining the internal cavity of the larva.""Here it grows and matures, an alien existence independent of the larval body structures, axis, bilateral symmetry, and form, imbued with a complete disregard for every embodiment of its larval stage." Eventually, the starfish emerges, and, most oddly, the larva continues on its way "swimming the pelagic waters and grazing on its vegetarian diet of algae". Essentially, the starfish develops from what might be called stem cells that are carried within the larva. It's all very alien, or perhaps even Alien.
The theory presented in Frank Ryan's The Mysteries of Metamorphosis (White River Junction, 2011) is that at one time the larva and the starfish were two different creatures (from two different phyla). Somewhere in the dark backward and abyss of time, sperm from the one creature encountered an egg of the other (both creatures eject enormous amounts of reproductive material into the sea) and cross-phyletic cross- fertilization occurred and the resultant chimera prospered.
Biologists resist the hypothesis because of the challenge it poses to the standard view ofthe evolutionary branching of life. I'm in no position to judge the theory's truth or falsity, but I'm attracted to the idea because it makes life forms so much more complex and unpredictable, and because it overturns conventional thinking.