Sea squirts digest their own brains when switching from larval to sessile forms.
Pyrosomes are bioluminescent colonial organisms.
Larvacea shed their skeletons every four hours.
Salps have two forms that alternate generations. The solitary form reproduces asexually by spawning a chain of hundreds of sequential hermaphrodites (female at first, male later on) that are all attached together. The hermaprodites release little embryos that grow up into solitary asexuals.
And Doliolida have the craziest life cycle I've ever heard of, where you basically get a "factory" form (complete with conveyor-belt organs!) that attaches some of its offspring to itself, to grow into feeder forms; some to its stalks, where they grow into "carrier ships"; and then some offspring to the carriers, which carry them far away and release them to reproduce sexually and generate more factories.
Nature is CRAZY, y'all.