I have been a busy little bee lately (well, that and I'm ill so I have nothing else to do anyway)
Updated version of this piece [link]
, including new ideas and features I've sorted out since then.
One of the major updates is that I've sorted out is the skeleton and musculature. If you compare this to the old one, you'll see that these have a more 'purposeful' form.
Their skeleton consists of a vertebral column which runs under the trunk of the body (as opposed to running above it in Earth vertebrates).
There are 3 girdles in the vertebrate skeleton, only the middle one now sports legs. The front and back have shrunken and become vestigial as legs, becoming antennae in pouchbacks and older vertebrates. In younger vertebrate species, it forms the 'squeaker'.