( a ) with organ-system level of organisation; they are bilaterally symmetrical, triploblastic and coelomate animals
( b ) with organ level of organisation; they are bilaterally symmetrical, triploblastic and acoelomate animals
( c ) with organ-system level of organisation; they are bilaterally symmetrical, triploblastic and acoelomate animals
( d ) with organ level of organisation; they are bilaterally symmetrical, diploblastic and coelomate animals
