Download 30.4 The Ecdysozoa

30.4 The Ecdysozoa
The ecdysozoans are protostomes, as are the trochozoa. The term ecdysis means
molting, and both roundworms and arthropods, which belong to this group,
periodically shed their outer covering.
Roundworms
Roundworms are nonsegmented worms that are prevalent in almost any
environment. They possess a pseudocoelom.
Ascaris
A female Ascaris is very reproductively prolific. They are most
commonly
parasites of humans and pigs.
Other Roundworms
Trichinosis is a fairly serious infection cause by eating pork that is not
fully
cooked that contains encysted larvae of the round worm
Trichinella spiralis.
Elephantiasis is caused by a roundworm
called the filarial worm. Pinworm and
hookworm infections are
more common in the United States.
Arthropods
Arthropods are extremely diverse. Over one million species have been
discovered and described. Arthropods have jointed appendages and an
exoskeleton made of chitin. They are segmented and have a well-developed
nervous system that includes a brain and a ventral solid nerve cord. They
have a variety of respiratory organs and have reduced competition through
metamorphosis.
Crustaceans
Crustaceans include barnacles, shrimps, lobsters, and crabs. They are
named for their hard shells.
Internal Organs
In the crayfish, the digestive system includes a stomach. The
coelom is reduced to a space around the reproductive system.
They have an open circulatory system. The nervous system is
very similar to that of an earthworm.
Insects
Insects are very numerous and diverse. Insects have a body that is
divided into a head, a
thorax, and an abdomen. The head bears
sensory antennae, a pair of compound eyes, and several simple eyes.
The mouthparts are adapted for the type of food. Wings may be
present.
Internal Organs
In the grasshopper, there is an excretory system, a respiratory
system, and a circulatory system.
Reproduction and Development
Metamorphosis is a change in form and physiology that occurs
as an immature stage, called a larva, becomes an adult.
Comparison with Crayfish
A comparison of a grasshopper with a crayfish reveals the
adaptations to a terrestrial environment.
Arachnids
The arachnids include scorpions, spiders, ticks, and mites. They have
six pairs of
appendages.