Priapulids, kinorhynchs, and loriciferans are relatively small, poorly known groups of wormlike marine ecdysozoans. Nematodes and horsehair worms have unsegmented wormlike bodies. Nematodes are among the most abundant and widely distributed animal groups.
learning outcomes
You should be able to:
Compare cuticle thickness in the different ecdysozoans and explain the consequences of such variation.
Explain why the nematode Caenorhabditis elegans is a widely used model system in laboratory research.
Explain why nematode diversity is important to global ecosystems.
Provide examples of nematodes that are human parasites.
How and why does cuticle thickness vary among the ecdysozoans?
In many wormlike ecdysozoans, the cuticle is relatively thin and flexible. This provides only modest body protection and support but allows the exchange of water, gases, and minerals across the body surface. Species in which the cuticle is thin are typically restricted to moist environments. In contrast, most arthropods have a thicker, more rigid cuticle that protects against dehydration and predation and provides support for muscle attachment, which allows for colonization of drier environments.
Describe at least three ways in which nematodes have significant impacts on humans.
Many nematodes act as scavengers in the soil and are important in decomposition and soil formation (which is critical to agriculture). The nematode C. elegans is an important model organism that is widely used by geneticists and developmental biologists. Other species of nematodes parasitize humans, causing diseases such as trichinosis and elephantiasis.
We will turn next to the animals that not only dominate the ecdysozoan clade but also constitute the most diverse group of animals on Earth.