Phylum Nematoda Flashcards - Chapter 18

Cuticle and Body Structure

• Cuticle is a non-cellular, tough body covering, secreted by the epidermis.
• Hypodermis is the cellular layer beneath the cuticle that produces it.
• Nematodes have a pseudocoelom filled with fluid, acting as a hydrostatic skeleton, surrounded by muscles and bounded by the cuticle.

Sensory Organs

• Amphids are circular, concentration sensory organs located at the anterior end, responsible for sensing the environment.
• Phasmids, located at the posterior end, are similar sensory structures also involved in environmental sensing.

Ecdysis and Growth

• Ecdysis refers to the periodic shedding or molting of the cuticle.
• Ecdysome hormone promotes ecdysis, essential for growth and development in nematodes.

Muscular and Locomotion Features

• Nematodes have longitudinal body-wall muscles that contract in a cylindrical shape, enabling a thrashing motion for movement.

Digestive System

• Nematodes possess an alimentary canal consisting of an open digestive tract with two openings: mouth and anus.
• The system includes structures such as the mouth, pharynx, intestine, rectum, and terminal anus.

Reproductive Characteristics

• Nematodes are dioecious, having separate male and female individuals.
• Fertilization is internal; males utilize copulatory spicules to hold the female's genital pore open and release sperm.

Taxonomy and Classification

• Phylum Nematoda is eumetazoan, triploblastic, and bilaterally symmetric.
• Classified into two main classes:
  • Secernentea: Parasitic forms with three esophageal glands and ventral coiled amphids (includes intestinal worms, hookworms, filarial worms, pinworms).
  • Adenophorea: Non-parasitic organisms with well-developed amphids and five esophageal glands (includes Trichinella, whipworm).

Characteristics of Nematodes

• Basic characteristics include pseudocoelom, triploblastic organization, extracellular digestion, elongated and cylindrical bodies, and lack of annuli, segments, and septum.

Life Cycle and Effects on Humans

• Ascaris lumbricoides: Found in intestines, feeds on intestinal fluids, causes weight loss, abdominal pain, and fatigue.
• Necator americanus: Hookworm feeding on blood and mucus, produces fatigue and anemia.
• Enterobius vermicularis: Pinworm residing in intestines causes itching and discomfort.
• Trichinella spiralis: Trichina worm found in intestinal tissues, leads to symptoms of muscle pain.
• Wuchereria bancrofti: Causes elephantiasis due to adult worms in lymphatics.

Key Terms Summary

• Hydrostatic pressure: The force exerted by fluids, crucial for maintaining body shape in nematodes.
• Copulatory spicules: Male nematode structures aiding in reproductive function.