Symbion pandora is a jug-shaped microscopic aquatic animal that dwells on the mouth-parts of Norway lobsters.

The animals are less than ½ mm wide, with sac-like bodies, and three distinctly different forms in different parts of their three-stage life cycle.

The phylum Cycliophora, from the Greek for 'carrying a small wheel', was named after the creature's circular mouth.

There are three basic life stages: Symbion pandora can reproduce both asexually by budding and sexually.

The sexual reproductive cycle is triggered when the host crustacean molts its skin in order to grow: a feeding stage buds a male, which attaches to another feeding stage and triggers it to bud a female, which it impregnates.