The first stage is called the Nauplius stage. The Nauplius larva emerges from its parent’s shell, ravenously consuming plankton. It then undergoes a surprising transformation, molting into its second stage: the Cypris stage. The interesting aspect of the Cypris larva is that it is non-feeding and a weak swimmer. The larva soon settles to the bottom and pulls itself with its antennae in search for a suitable home: rocks, dock pilings, boats, mussels, or even whales. After selecting a spot, the barnacle secures itself head-first to the surface with a very strong brown glue, now being studied by dentists for its adhesive properties. The larva soon begins to metamorphose into an adult and to build its tough housing. The barnacle secretes six calcareous plates that totally encase the animal. Four more plates are secreted to form a ‘door’ that the barnacle can open or close depending on the tides. When covered by water, the barnacle rythmically opens its trapdoor to extend its feathery feet, called ‘cirri’, into the water, trapping plankton to eat. The legs also have gills for gas exchange
Most barnacles are hermaphrodites, meaning that one barnacle has both male and female sex organs. To reproduce, however, they indulge in cross fertilization. A retractable tube containing sperm reaches outside the shell as far as several inches to another barnacle to copulate.
All true crabs are in a subgroup of crustaceans called Brachyura. All crabs have four pairs of walking legs and two legs with claws. The edge of their shell is often toothed. They move sideways, holding their claws from their body. It is usually easy to determine a crab’s sex by turning a crab over and examining its abdominal flap. Female crabs have a wide abdomen to hold eggs, while males have a thin, pencil shaped flap. Crab eggs hatch and mature in three stages: a zoea stage, bearing no resemblance to the adult, a megalops stage, resembling a small lobster, and an adult stage. Zoea and megalops larvae live in the water with other plankton. After four or five weeks of drifting in ocean currents, a zoea molts to a megalops, which lives about a week then molts to a tiny crab that can swim or walk on the muddy bottoms. Through a series of further molts, the juvenile crab becomes an adult.