Simplify the following text for a Grade 9 native English-speaking person.
Original: Each segment bears a pair of paddle-like and highly vascularized parapodia , which are used for movement and , in many species , act as the worm 's primary respiratory surfaces .
Simplified: Each segment bears a pair of paddle-like parapodia , which are used for movement . In many species , the parapodia , well supplied with blood vessels , act as the worm 's primary respiratory surfaces .