Short spines do Thr imp damage based on the lower of the ST of the attacker or the victim and cost 1 point. Medium spines do Thr+1/die imp and cost 2 points. Long spines do Thr+2/die imp and cost 3 points.
Spines can have limited coverage. This is a -60% limitation. You do not get a free action to hit in close combat, and you need to make a DX roll to damage those who slam or grapple you. You automatically do damage if swallowed, however.