Energy and Modes of Nutrition in Nematodes
On the most basic level, nematodes are consumers. As was discussed in the ecological roles of nematodes, free living roundworms are essential to the energy and matter cycles in the biosphere. They feed on microorganisms as well as decaying organic matter. Nematodes utilize food sources to gain energy, often in the form of glycogen, and form new tissues (Poinar Jr. 39).
Nematodes are almost entirely aerobic when it comes to respiration because they metabolize using oxygen from the surrounding environment. This oxygen gas diffuses through their body wall thus effectively eliminating the need for circulation or specific respiratory organs. Often, nematodes are found in environments that are low in oxygen, but they seem to be able maintain relatively normal growth. In these situations, adaptations in metabolism have not been highly studied (Poinar Jr. 47)
All nematodes possess a similar digestive system or tract that consists of a mouth, sometimes referred to as a stoma, the pharynx or esophagus, and the intestine. While present in all nematodes, there is some room for variation of these structures based on the feeding habits of the different species (Poinar Jr. 40-45). The most important types of nematode feeding or trophic groups, as described by Robert McSorley on his Featured Creatures website, include:
Algivores-Nematodes found in aquatic environments and rarely in soil that feed primarily on algae.
Herbivores-Plant parasitic nematodes comprise this classification. They all have modified mouth structures and use a “stylet” or needlelike protrusion to pierce cells during feeding. These parasites can be divided into either Ectoparasites and Endoparasites (those that stay in the soil and those that enter the plant through the root). The stylet can be seen in the herbivore mouthpart diagram provided below.
Image obtained from http://creatures.ifas.ufl.edu/nematode/soil_nematode.htm
Bacterivores-Those free living roundworms whose primary source of food is bacteria; they help in decomposing organic matter. As is shown in the diagram above, bacterivore mouthparts reflect their food source in the fairly open space where soil and other organic matter is taken in.
Fungivores-A group of nematodes that uses a “style to puncture fungal hyphae,” thus feeding mainly on fungi; they are also important in decomposition.
Predators- Nematodes whose primary source of food is small animals and other nematodes of similar size: they are less common than most other types of nematodes.
Omnivores- A few types of nematodes may be able to feed on several different types of food and are thus considered omnivorous.
Animal Parasites- Those nematodes that inhabit animal hosts in their tissues, intestinal tracts, and other organs and derive their nutrition from the host.
Unknown- Due to the extremely limited study of nematodes, there are probably many different food sources and feeding habits that have not yet been discovered (McSorley 2004).
Evolution & Phylogenetic Relationships
Features Shared by Nematodes with Related Groups
Features Unique to Nematodes
World Distribution of Roundworms
Nematode Habitat Use
Energy/Modes of Nutrition
Ecological Roles of Nematodes
Impacts on Human Society