Question

Unlike all other chordates, tunicates and lancelets are primarily stationary during adulthood. What adaptation allows vertebrates greater mobility?
1. development of an exoskeleton
2. development of jointed appendages
3. development of the notochord into a backbone consisting of vertebrae
4. development of bilateral body symmetry

Answer 1

see this http://wiki.answers.com/Q/What_adaptation_allows_vertebrates_greater_mobility

Answer 2

3. development of the notochord into a backbone

Answer 3

1 - do we have an exoskeleton? duh. plus, exoskeleton inhibits growing, because it's too heavy.
2 - who has unjointed appendages?
3 - that sounds about right...at least I got a backbone.
4 - they nearly all have a bilateral body symmetry, plus that doesnt account for mobility.