nematodi

Nematodi, commonly referred to as nematodes, are a diverse group of roundworms belonging to the phylum Nematoda. They inhabit nearly every ecosystem on Earth, including soil, freshwater, marine environments, and the internal tissues of plants and animals. With thousands of described species and many more likely undescribed, they represent one of the most abundant and varied animal groups.

Morphology and biology

Nematodi are typically slender, elongated, and unsegmented, with a flexible external cuticle and a hydrostatic skeleton. They possess a pseudocoelom, a simple tubular digestive system, and a nervous system with a few nerve cords. Gas exchange and excretion occur primarily through diffusion across the body surface. Many plant-parasitic species feed with a specialized mouthpart called a stylet, while others are free-living decomposers or predators. They lack specialized circulatory and respiratory systems.

Life cycle and reproduction

Most nematodi reproduce sexually, having separate males and females, though some species are hermaphroditic or reproduce by parthenogenesis. Development commonly includes four juvenile stages (L1–L4) before adulthood, with molts between stages. Life cycles range from free-living to obligate or facultative parasitism of plants, animals, or humans.

Ecology and significance

Nematodi play key roles in ecosystems as decomposers and regulators of microbial communities. Economically, parasitic species cause substantial agricultural losses by damaging roots and reducing crop yields (for example, Meloidogyne and Heterodera groups). Parasitic nematodes also affect livestock and humans, contributing to a range of diseases. Conversely, some nematodi, notably Caenorhabditis elegans, are important model organisms in science and medicine. Management and research focus on understanding their biology, life cycles, and interactions with hosts and environments.