Nematode
Overview
Nematodes, or roundworms, constitute the phylum Nematoda. They are a diverse animal phylum inhabiting a broad range of environments. Nematode species can be difficult to distinguish, and although over 25,000 have been described, of which more than half are parasitic, it is estimated that the actual number is probably closer to a million.
Morphology
Nematodes are typically slender worms: most are less than 1.2 mm (0.047 in) in diameter, although the largest species, such as the giant roundworm of whales, can reach lengths of up to 3 m (9.8 ft). They are often overlooked because of their size. Nematodes may be colorless, or occasionally white, yellow, brown, or black. The body is often ornamented with ridges, rings, bristles, or other distinctive structures.
Anatomy
The nematode body is essentially a tube within a tube, the outer tube being the body wall, and the inner tube being the gut. The body cavity is a pseudocoel, a body cavity that is not entirely lined by mesoderm. The mouth often includes a sharp stylet, which the animal can thrust into its prey.
Life Cycle
The life cycle of a nematode is relatively complex compared to other organisms. The nematode life cycle consists of an egg, four larval stages and an adult. Most nematode species are dioecious, with separate male and female individuals, though some, such as Caenorhabditis elegans, are hermaphroditic.
Ecology
Nematodes play crucial roles in the earth's ecosystems. They are an integral part of the soil food web. Nematodes contribute to nutrient cycling and the decomposition process. They are often the most numerous multicellular animals in soil. Many nematodes are free-living, while others are parasites of plants, animals, or other nematodes.
Economic Importance
Nematodes have a significant impact on agriculture. Some species of nematodes act as parasites on plant roots, causing damage to crops and resulting in significant economic losses. Other nematodes are beneficial, playing a role in the decomposition process and in controlling pests.
Research
Nematodes, particularly Caenorhabditis elegans, have been used extensively in research. They have been instrumental in providing fundamental insights into developmental biology, neurobiology, and apoptosis.