Arthropoda

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Arthropoda
Mollusca
Echinodermata
Cnidaria

Arthropods are one of the most successful group of animals in the world in terms of their numbers. Majority of the marine Arthropods belongs to the Crustacea class. This is also the first phylum in which a large percent of its members that are well adapted to living in the terrestrial environment. In contrast to their terrestrial relatives (i.e. spiders), the Crustaceans are solitary animals that prefer to hide in crevices, under rocks, or in abandoned snail shells (i.e. hermit crabs) .

One of the primary defense mechanism of the Arthropods is the exoskeleton that gives their body its shape, colour, texture, and support. Some Arthropods however, have developed over means of improving their chances in survival. The hermit crab for instance, takes on abandoned snail shells to protect their tails. Other crab species, such as the decorators crabs, try to remain invisible to predators by attaching debris to the tops of their exoskeletons. The Arthropods are also capable of regenerating limbs that have been taken off by predators to further increase their chances of survival in the unforgiving sea.

Characteristics:
bullet Exoskeleton - a strong, lightweight, external covering and support
bullet Striated Muscle - quick, strong, yet lightweight form of muscle that makes rapid movement possible
bullet Jointed Appendages - See the lobster picture above
bullet Molting - growth progresses in steps with shedding off of the old exoskeleton in exchange for a new and larger shell

Marine Invertebrates Belonging to this Phylum:
bullet lobsters
bullet crabs
bullet krill
bullet barnacles
bullet shrimps
Their terrestrial relatives includes some of the most hated insects such as spiders, cockroaches, and flies.

Appearance wise, barnacles closely resemble the Molluscs; however, they have jointed feet and exoskeleton just like the other Arthropods.

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March 25, 2004