Sharks and remora fish work together.

The remora fish attaches to the belly of the shark by a sucker disc in it's mouth. It travels everywhere the shark goes. It eats any parasites on the shark which helps keep the shark clean. It also eats any leftover food from the shark. The remora (sucker fish) gets to eat and the shark stays clean and healthy.

http://animalsymbiosis.weebly.com/sharks-and-remora-fish.html

http://aquaviews.net/explore-the-blue/shark-remora-relationship/

http://animaldiversity.org/accounts/Remora_remora/

http://sp11symbiosis.providence.wikispaces.net/Shark+symbiosis+with+Pilot+and+Remora+fish

http://www.underwaterjournal.com/attack-of-the-shark-sucker/