Crustaceans are characterized by a hard exoskeleton and jointed legs. The shell is composed of 6 overlapping plates with an opening at the top covered by two hard flaps. When the barnacle is submerged in water, the two flaps, acting as doors, open up. The barnacle unfolds a fan of feathery appendages. Upon closer inspection, one can distinguish the jointed legs which make up this fan.
Barnacles are hermaphroditic, each individual possessing both male and female organs.
To reproduce, however, a barnacle's eggs must be fertilized by another individual. This is accomplished by a sperm tube that protrudes from one barnacle into a neighboring one. Fertilized eggs are nurtured in the barnacle until they hatch into tiny larvae and are released into the water during May and June. Barnacle larvae are a favorite and abundant food source for many young fish and are consumed in large numbers. Barnacle larvae pass through two stages.