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For educational purposes only; do not review, quote or
abstract:-- Information on
the basics of Invertebrate Zoology |
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An Introduction To The
Study of Invertebrate Zoology Kingdom: Animalia, Phylum: Acanthocephala (Contact)
CLICK on underlined file names and included illustrations to enlarge: The Phylum Acanthocephala derives its
name from "spiny-headed." All
species are parasites in the digestive tract of vertebrates with intermediate
hosts that are generally arthropods.
The anterior end of the animal has a probosis with spiny hooks. A representative genus is Macracanthorhynchus
with characteristics noted as follows: General Body Features.-- A retractable proboscis
is present. There is a genital pore
at the posterior end, which in the female is very simple and in the male is
an inflatable fan-like affair or bursa that is used for copulation. The female is larger than the male. Body Wall.-- A heavy cuticle is present. Underneath the cuticle and secreting it
lies the epidermis. All cell
membranes are lost between the cells, a condition that is known as a syncytium.
In the syncytium nuclei are scattered through an undivided mass of
cytoplasm. Both circular and
longitudinal muscles are well developed and lie under the epidermis. The muscle cells consist of tapering
hollow cylinders .
Pseudocoelom.-- This
structure differs from a true coelom in not being derived entirely from the
mesoderm. In a true coelom the body
cavity is lined on all sides by mesoderm.
However, it serves the same purpose as a true coelom. It takes up practically all of the
interior of the animal. Inside the
pseudocoelom there is a fluid, which maintains turgor. Food & Digestion.-- There is no mouth or any
sign of a digestive tract, and thus the animals are similar to the
Cestoda. Predigested food is absorbed
through the body wall. Respiration.-- The animals respire by diffusion
and it is anaerobic for considerable periods. Excretion.-- Flame cells, which are not
scattered, accomplishes excretion.
They are gathered into two large tufts projecting out into the
pseudocoelom and emptying out through the reproductive tract (= urogenital system). Nervous System.-- A simple nervous system
is present consisting of a single ganglion, which lies on the outer wall of
the proboscis sheath. Various nerves
run out to different parts of the body particularly to the muscles. This is then much simplier than that of
the Turbellaria.
Reproduction.--
Extending the whole length of the body and dividing up the pseudocoelom in
sections are suspensory ligaments. The male has two testes attached to a
suspensory ligament, and the vas eferens and vas deferens are present. There are a series of 6-8 cement glands on the sides of the vas deferens,
which lead back to the copulatory bursa that serves
an adhesive funtion during copulation.
The female has a series of ovaries attached to the
suspensory ligaments. Floating ovaries are present, which are
little patches of ovary tissue that break off of the main ovary and bear the
maturing ova. The eggs when mature
detach from the ovaries and they too float in the fluid of the
pseudocoelom. Eggs are fertilized in
the pseudocoelom by the sperm that enter the cavity. Eggs with developing embryos bear 2-3
heavy shell layers. At the opening of
the female genital tract is a remarkable structure, the uterine
bell, which is a selective apparatus.
Fluid of the pseudocoelom is sucked into the mouth of
the apparatus. A selection of mature
eggs is made at the base and immature eggs are passed back into the pseudocoelom. The mature eggs are laid outside following
selection that is made on the basis of size and shape of the egg. Lemnisci.-- These are
glandular structures, which occur at the anterior end of the animal. They are part of the lacunar system that runs all through the
epidermis. They may serve as
reservoirs for fluid, which moves around the lacunar system. Cell Constancy.--
There is a definite number of cells per each organ, thus the number of
epidermal, muscular, nerve cells, etc. is constant per species. This results in a cessation of cell division
in the late embryonic period of development, except for the ovaries and
testes. All further increase in size
is due to the enlargement of existing cells.
Various parts of the body consist of definite numbers of cells (except
the gonads). Along with this there is
a tremendous increase in the size of the nuclei. A syncytium frequently results. Life History.
-- Macracanthorhynchus is a parasite of pigs. The eggs pass out with the host's
faeces. June beeetle larvae consume
the eggs and the embryo leaves the egg and bores through to the body cavity
of the beetle. The hog must devour
the beetle to complete the life cycle.
Different species of parasite have different intermediate hosts of
aquatic insects and crustaceans, etc. Importance.--
There is relatively little economic importance although infection by Macracanthorhynchus
may lower the general health of the pig if present in large numbers. ------------------------------------ Please see following plates for Example Structures of the
Acanthocephala: Plate 29 = Phylum: Acanthocephala:
Macracanthorhynchus sp. male Plate 30 = Phylum: Acanthocephala:
Macracanthorhynchus sp. --
Cross-sections Plate 31 = Phylum: Acanthocephala,
Macracanthorhynchus sp. --
Dissected Female specimen ============== |
