A moderately large order of nematode

Nematode

The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...

s. Aphelenchida have a stylet

Stylet

A stylet is a hard, sharp, anatomical structure found in some invertebrates.For example, the word stylet or stomatostyle, is used for the primitive piercing mouthparts of some nematodes and some nemerteans...

 for feeding and a very prominent median bulb in the oesophagus. They are cosmopolitan. Some are associated with insect

Insect

Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s, and may be ectoparasites or endoparasites, or merely use the insect

Insect

Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

 as transport. Others are associated with plant

Plant

Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

s, as root

Root

In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...

, stem

Plant stem

A stem is one of two main structural axes of a vascular plant. The stem is normally divided into nodes and internodes, the nodes hold buds which grow into one or more leaves, inflorescence , conifer cones, roots, other stems etc. The internodes distance one node from another...

, or leaf

Leaf

A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....

 parasites, which may be pathogenic to the plant or not. Still others are associated with fungi, and some are free-living. There may be considerable plasticity of feeding habits within species, involving almost any combination of the categories listed above. Sometimes different feeding habits involve morphologically distinct phases, but they may involve only behavioral differences, and sometimes depend only on the immediate availability of different foods. Some life cycle

Biological life cycle

A life cycle is a period involving all different generations of a species succeeding each other through means of reproduction, whether through asexual reproduction or sexual reproduction...

s involve a definite progression of particular hosts and depend on the life cycle of the host. Fungal feeders may have life cycles as short as 5 days.

This order includes:

• Aphelenchidae
• Aphelenchoididae
• Myenchildae
• Paraphelenchidae