free-swimming
adjective
free-swim·ming ˈfrē-ˈswi-miŋ 
: able to swim about : not attached
the free-swimming larva of the barnacle
Word History
First Known Use
1841, in the meaning defined above
Medical Definition
free-swimming
adjective
free-swim·ming -ˌswim-iŋ
: able to swim about : not attached
a free-swimming larva of a trematode