Animals with a flexible rod supporting their dorsal or back sides.

Body symmetry where the body can be divided into two identical halves in only one plane.The right and left sides of the body are exactly the mirror image of each other.

of or involving the mouth or mouth region or the surface on which the mouth is located. 

situated opposite or away from the mouth

relating to the upper side or back of a body or organ.

relating to the underside of a body; abdominal

to the side of, or away from the middle of the body.

towards the middle or center

Organisms lacking external symmetry; unequal parts

immature age of an insect between egg and pupa.

The process of transformation from an immature form to an adult form in two or more distinct stages.