The Open Door Web Site
Part XV : Animal Dispersal Index
Adult barnacles on the shell of a mussel
Changing Shape to Travel Better : Crustaceans
Crustaceans, except for one or two exceptions, live in water. The adult crustaceans are often either fixed in one position or slow-moving. The adults liberate their eggs into the water and it is in the water that the eggs are fertilized.
There are a wide variety of larvae which live in the seas and oceans. These larvae are microscopic and can easily move with water currents and tides. They join the millions of animals and plants in the plankton.
The larvae often look very different from the adult forms when they are small. They gradually change their shape as they grow, however, and start to resemble their adult forms in miniature. Eventually the growing larvae become too heavy to stay with the plankton. The miniature adults then leave the plankton to find a suitable habitat to live out the rest of their lives.
Drawing showing the life cycle of the barnacle
The nauplii swim in the open ocean. They feed on phytoplankton and the grow by moulting their exoskeletons six times.
An example is the barnacle. Barnacles are common on rocky sea shores. Adult barnacles are firmly fixed to rocks by a type of cement. They live closely packed together, however, so they can easily mate. They are hermaphrodite, which means that every barnacle can be both male and female, but not at the same time. This means that every barnacle is capable of producing eggs which can be fertilized by a neighbour which is in its male phase.
The larvae are released from the adult when they hatch from their eggs. These larvae are called nauplii (singular nauplius). The nauplii join the plankton.
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