Phylum Acanthocephala (spiny headed worms)
- Separate sexes; sexual dimorphism present.
- Body comprised of proboscus, neck and trunk.
Acanthocephala consists of the three
classes Archiacanthocephala, Eoacanthocephala, and
Palaeacanthocephala. All members are bilaterally symmetrical and
cylindrical in shape. The adults live in the intestines of
vertebrates and the larvae (acanthor) live in the tissues of
crustaceans and insects. The body is composed of a neck, a long trunk
and a proboscus which bears retractible hooks. The body plan is
pseudocoelomic with no apparent digestive tract, although a flame bulb
system is evident. The body wall is made of a cuticle and thick
syncitial hypodermis with circular and longitudnal muscle fibers. The
adult male has a full complement of reproductive organs and the female
has only a large number of eggs.
Some Interesting Facts:
- Acanthocephalans parasitize a variety of vertebrate hosts
including the birds, reptiles, fish and mammals.
- The life history includes an arthropod intermediate host and a
vertebrate definitive host. When the eggs are excreted with the feces
of the definitive host, the proper arthropod intermediate ingests
them. The larva are then liberated and attach to the gut lining. In the
arthropod cavity, the acanthor develops into an infective cystacanth
where it further develops into maturity.
- Among parasitic adaptations is the reduction of the muscular,
circulatory, and excretory systems.
- There is complete absence of
the digestive tract.
There are two slides (wm) and preserved specimens. What are the
similarities between this phylum and the nematodes? One major difference
is at the anterior end of the animal. Make a sketch of the whole animal
and an exploded sketch of the anterior end. Is this structure similar or
different to equivalent structures in the cestodes?
Pertinent Books Found in Lamson Library:
- Parker, Sybil P. 1982. Synopsis and Classification of Living Organisms.
New York: McGraw Hill Company.
- Pennak, Robert W. 1964. Collegiate Dictionary of Zoology.
New York: Ronald Press Company.
(Michele L. Cote, Fall 1994; edited B. Miller Spring 1995)