Metamorphosis in Action

Sea squirts, or ascidians, are some of our closest invertebrate relatives. They are classified as chordates because they develop indirectly through a 'tadpole' larval stage. Ascidian tadpoles have notochords, dorsal nerve tubes, and pharyngeal slits just like their vertebrate amphibian counterparts. Not that they're phylogenetic neighbors. 

Development and its results in ascidian versus amphibian larvae are dramatically different. Ascidian tadpoles are lecithotrophic: the mouth is closed off from the gut, and the larva depends on maternally furnished yolk as fuel through metamorphosis. When an ascidian tadpole finds a place to settle, it anchors with an adhesive secreted from its anterior papillae and begins to absorb its own tail, notochord and all. 

You can see the middle part of that process here, in a video of Ascidia ceratodes (fert. 5/6/14.)

The ascidian might take three hours or so to absorb its entire tail. A few days later, its mouth will open and filter-feeding begins!

Thanks to http://chordate.bpni.bio.keio.ac.jp/faba2/2.2/developmental_table.html and Strathmann for an idea of what to expect in the development timeline.

Video is 30 s interval time lapse shot at 100X under DF illumination.