Zoology · Ch 2 — Kingdom Animalia
Phylum Aschelminthes (Round Worms)
Phylum Aschelminthes (Round Worms)
Aschelminthes (Greek askes, cavity; helminths, worms) — previously classified as Nematoda — are the round worms, named for their circular cross-section. They are triploblastic, bilaterally symmetrical, pseudocoelomate animals with organ-system organisation, and may be free-living or parasitic on aquatic and terrestrial plants and animals.
The unsegmented body is covered by a tough, transparent, protective collagenous cuticle. Unlike the flatworms, Aschelminthes have a complete alimentary canal, with a well-developed mouth, a muscular pharynx, and a separate anus — the first phylum in the classification scheme to achieve this. Their excretory system is built around specialised gland cells rather than flame cells. …
What this figure shows. Three cylindrical, unsegmented round-worm bodies tapering at both ends and covered by a smooth cuticle: Ascaris (the large intestinal roundworm, with a visibly longer, thicker female and a shorter, curved-tailed male, illustrating sexual dimorphism); Filarial worm (Wuchereria bancrofti), a fine thread-like worm; and Hook worm (Ancylostoma duodenale), a small worm with a curved anterior end bearing hooks or cutting plates for at …