PHYLUM ASCHELMINTHES; PHYLUM ACANTHOCEPHELMINTHES;
ARTHROPODS AND VECTORS
Section I: PHYLUM ASCHELMINTHES
This phylum consists of thousands of free living and parasitic species. They are
round with tapering ends and unsegmented. Members of this phylum have been found
to be parasitic in nearly every type of organism and in every system of the body. All of
the human parasitic round worms belong to the class Nematoda. The life cycle of
nematodes varies from simple autoinfection to a complicated cycle that carries the larval
organism through different systems of the host before arriving at the natural habitat.
Reproduction is sexual and two organisms, one of each sex, are required (dioecious).
The female is considerably larger than the male, and the males have curved tails and/or
specialized copulatory organs that aid in grasping the female for copulation. The outer
covering, the cuticle, is relatively impermeable, used for protection, and molting from
one larval stage to another begins here. The digestive tract is complete and consists of
a mouth, a specialized pharyngeal area, intestines, rectum, and an anus. These
organisms possess a sophisticated osmoregulatory/excretory system based on
ammonia waste that exits through the anus. Some species may have excretory pores
and/or renette glands. The nervous system consists of two nerve rings (anterior and
posterior) that lead to receptors (sense organs) for light, chemical, and mechanical
stimulation, and a pair of longitudinal nerves located laterally.
Nematodes parasitic to man can be grouped according to life cycles, as; A.
Intestinal Nematodes, B. Tissue Dwelling Nematodes, and C. Blood and Tissue