Cercariae are produced asexually and in large numbers by all digeneans. Their form varies quite markedly among species, and in many cases they can be identified quite easily to family and often to genus. This is because the body, or soma, of the cercaria resembles a miniature adult. This cercaria possesses a simple, straight tail, two suckers (the acetabulum is in the mid-body region), and a circle of spines on a collar around the oral sucker. The dark lateral bands just anterior to the acetabulum are parts of the excretory system, which is prominent in cercariae but much less noticeable in the adult worm. The excretory system is important to cercariae because they are hyperosmotic to the aquatic medium they spend their brief life in.