Nematodes – Key Vocabulary

A vocabulary set covering morphology, physiology, reproduction, and notable parasitic and free-living nematodes mentioned in the lecture.

Nematodes (roundworms)

Phylum of unsegmented, cylindrical worms with tapered ends and a complete digestive tract.

Habitat versatility

Ability to live in marine and fresh waters, hot springs, soil, leaf litter, and animal body fluids or intestines.

Bilateral symmetry

Body plan in which the left and right sides are mirror images along a single plane.

Triploblastic

Having three embryonic germ layers: ectoderm, mesoderm, and endoderm.

Pseudocoelom

Fluid-filled body cavity not fully lined by mesoderm; acts as a hydrostatic skeleton in nematodes.

Hydrostatic skeleton (hydroskeleton)

Body support system produced by pressurized pseudocoelomic fluid combined with longitudinal muscles.

Cuticle

Thick, multi-layered, non-stretchable external collagenous covering that protects the nematode body.

Molting (ecdysis)

Periodic shedding of the cuticle that allows growth; nematodes grow mainly right after molting.

Hypodermis

Single-layered epidermis beneath the cuticle that forms four longitudinal thickenings called hypodermal cords.

Longitudinal muscle layer

Single layer of muscle cells running lengthwise beneath the hypodermis; responsible for thrashing motion.

Absence of cilia/flagella

Nematodes lack motile appendages even on sperm cells, relying on other mechanisms for movement.

Complete digestive system

Alimentary canal with mouth, buccal cavity, muscular pharynx, intestine, and anus.

Buccal cavity

Mouth chamber that may bear cuticular stylets, teeth, or plates for piercing or macerating food.

Stylet

Hard, needle-like cuticular structure used by some nematodes to puncture host tissues and suck fluids.

Extracellular digestion

Enzymatic breakdown of food within the intestinal lumen rather than inside cells.

H-shaped excretory system

Pair of longitudinal excretory canals connected by a transverse canal, opening ventrally near the head.

Osmoregulation

Regulation of water and ion balance; main function of the nematode excretory system.

Ammonotelic

Excreting nitrogenous waste primarily as ammonia.

Fagocytic (fagocyte) cells

Special cells that trap and store insoluble metabolic wastes within the pseudocoelomic fluid.

Cutaneous gas exchange

Diffusion of gases across the entire body surface; nematodes lack discrete respiratory organs.

Anaerobic metabolism

Energy production via fermentation, common in parasitic nematodes living in low-oxygen habitats.

Lack of circulatory system

Transport of nutrients and wastes occurs through movement of pseudocoelomic fluid, not blood vessels.

Dioecious

Having separate male and female individuals.

Sexual dimorphism

Morphological difference between sexes; males are usually smaller with a ventrally curved posterior end.

Internal fertilisation

Sperm transfer takes place inside the female reproductive tract.

Oviparous

Reproductive mode in which females lay eggs that develop outside the body.

Viviparous

Giving birth to live young; occurs in some nematode species (e.g., Trichinella).

Direct development

Life cycle lacking a free-living larval stage; juvenile resembles a small adult.

Invasive egg

Fully embryonated egg capable of infecting a new host once environmental conditions are suitable.

Ascaris lumbricoides (human roundworm)

Large intestinal nematode of humans; causes ascariasis and can lay ~200,000 eggs per day.

Ascariasis

Intestinal disease produced by Ascaris infection, often acquired by ingesting contaminated produce or water.

Trichinella spiralis (pork worm)

Viviparous nematode whose larvae encyst in striated muscles; transmitted by eating raw or under-cooked pork or game.

Trichinosis

Disease caused by Trichinella larvae encysted in human muscles, leading to fever, muscle pain, and potential organ damage.

Enterobius vermicularis (pinworm)

Common human intestinal nematode causing perianal itching; infection via hand-to-mouth transfer of eggs.

Trichuris trichiura (whipworm)

Human gut nematode with a whip-like anterior end; infection through ingestion of embryonated eggs in soil or produce.

Hookworm (Ancylostoma duodenale / Necator americanus)

Blood-feeding intestinal nematode entering the host through skin; leads to anemia.

Wuchereria bancrofti (Bancroft’s filaria)

Mosquito-borne nematode residing in lymph vessels; chronic infection causes lymphatic filariasis (elephantiasis).

Cyst nematodes (Heterodera/Globodera)

Plant-parasitic nematodes attacking beet and potato roots; females form resistant cysts.

Vinegar eel (Turbatrix aceti)

Free-living, acid-tolerant nematode often found in fermenting fruit and wine vinegar.