Title: Phylum Aschelminthes | Introduction to Medical Parasitology
Headings: Introduction to Medical Parasitology
Phylum Aschelminthes
Class Nematoda
Generalized structure of male (A) and female (B) nematode
Introduction to Medical Parasitology

Content: Phylum Aschelminthes | Introduction to Medical Parasitology
Jan
24
Phylum Aschelminthes
Six different classes, dominated by the Class Nematoda, represent Aschelminthes as a phylum. The nematodes (Nema, thread) or roundworms are ubiquitous small worms that dwarf in numbers all other groups of multicellular animals except insects and mites. Aschelminthes are pseudocoelomate, unsegmented worms that are covered with a cuticle. An unusual aschelminth trait is parthenogenesis (development of an unfertilised egg). In the classes Nematoda, Rotifera and Gastrotricha, males may be lacking and successive generations of females are produced parthenogenetically
Still another remarkable characteristic of the phylum is the consistency of cell numbers (eutely), in which a precise and relatively small number of cells, remaining unvaried throughout the animal’s life, comprise both specific organs and the entire animal. The number, constant not only for the species but also for the taxonomic group, can be used as part of its morphological definition (for example, the central nervous system in Ascaris and many other nematodes consists of 162 cells)
Class Nematoda
The class Nematoda is very important to us among the group as it consists of parasites of medical and veterinary importance. The class is characterized by the presence of a complete digestive system, consisting of a mouth, intestine, anus and absence of cilia. Nematodes are found practically in every ecological setting. They live in animals and plants as parasites and in mud, marine, fresh and brackish waters, soil and mud as free-living organisms. They vary in size from a few microns to slightly over a meter in length.