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