In zoology|lang=en terms the difference between balanoid and balanid
is that balanoid is (zoology) resembling an acorn; applied to a group of barnacles with shells shaped like acorns while balanid is (zoology) any member of the balanidae.
As an adjective balanoid
is (zoology) resembling an acorn; applied to a group of barnacles with shells shaped like acorns.