This strange animal comes from a cross between a dog and a fish it is a member of the sub class Elasmobranchii (which includes sharks, skates and rays). To see its insides: http://gallery.beefalo.org.uk/Dogfish
Dogfish, like dogs, can be trained to retrieve thrown items. Unfortunatly due to it's shared genes with fish you can only throw things as far as the dogfish can swim in 3 seconds due to it's short memory span.