nematodes

• NEMATODES:

  • Also known as roundworms.

  • Among the most abundant animals on Earth.

  • It is estimated that 75% of all nematode species are free living in marine, freshwater, and soil habitats.

  • There are about 500,000 species of nematodes. 10,000 have been described.

  • About 2,000 species of nematodes parasitize plants.
• GENERAL CHARACTERISTICS:

  • Unsegmented

  • Measures 2mm in length to a meter.

  • Sexes are separates (dioecious)

  • Males are smaller than females

  • Posterior portion of the male is curved or coiled.
• FORM AND FUNCTION:

  • Bilaterally symmetrical, elongated, and tapered at

  both ends.

  • Possess a pseudocoel.

  • The lumen of the pharynx is characteristically

  triradiate.

  • Body is covered with a non-cellular cuticle secreted

  by an underlying hypodermis
• Body wall pf nematodes consists of cuticle, hypodermis, and body wall musculature.
• COMPOSITION OF CUTICLE:

  • Cortical – outer most zone and contains a highly resistant protein called cuticulin.

  • Median – contains fine striations

  • Basal zone – composed of two or three fibrous layer.
• NERVOUS SYSTEM:

  • Relatively simple.

  • Most prominent feature is the nerve ring or circumesophageal commissure.

  • Presence of ventral, lateral and dorsal cephalic ganglia.

  • Presence of sensilia (small sense organs).
• DIGESTIVE SYSTEM:

  Mouth is usually a circular opening surrounded by a maximum of six lips located in the anterior ends.

  • Buccal cavity is tubular, or funnel shaped which for some specie is expanded for sucking purposes.

  • Food ingested moves into a muscular region of the tracts known as esophagus, which is important for identification of the specie.
• EXCRETORY SYSTEM: •

  There are two basic types of excretory systems namely glandular type and tubular type.

  • Presence of a median ventral duct and pore called the excretory pore
• REPRODUCTIVE SYSTEM (MALE):

  • The male reproductive organs are situated in the posterior third of the body as a single coiled or convoluted tube.

  • Various parts are differentiated as testis, vas deferens, seminal vesicles, and ejaculatory duct.
• REPRODUCTIVE SYSTEM (FEMALE):

  • The female reproductive system may either be a single or bifurcated tube, differentiated into ovary, oviduct, seminal receptable or uterus, ovijector, vagina and vulva that opens to the exterior.
• CLASSIFICATION OF FEMALE NEMATODES:

  • Oviparous – producing eggs that develops and hatch outside the body.

  • Larviparous/Viviparous – producing living larva young instead of eggs.

  • Parthenogenic – a form of reproduction in which viable egg develops into a new individual even without the male adult.
• CLASSIFICATION OF MEDICALLY SIGNIFICANT NEMATODES:

  • Based on the presence and absence of caudal receptor.

  o Class Enoplea – caudal receptor and caudal gland present.

  Trichuris trichiura. o Trichenlia spiralis. o Capillaria philippinensis.
• Class Rhabditea – with caudal receptor but without a caudal gland.

  o Ascaris lumbricoides

  o Strongyloides stercoralis

  o Enterobius vermicularis

  o Hookworm
• CLASSIFICATION BASED ON HABITAT:

  • SMALL INTESTINE

  o Ascaris lumbricoides

  o Capillaria philippinensis

  o Hookworms

  o Strongyloides stercoralis

  • LARGE INTESTINE

  o Trichuris trichiura

  o Enterobius vermicularis
• where do nematodes live

  marine, freshwater and soil