Annelids are a phylum including earthworms, leeches, polychaete
worms, and some other worm groups(3). Annelids are also called
segmented worms because a defining feature they all share is a
body most of which is divided into segments, each of which
contains parts of the basic body systems (2). This segmentation,
or metamerism, allows annelids to move more efficiently and
provides other benefits as well(2). Inside all of these
segments, in a cavity known as the coelom, is fluid that presses
against the annelid’s body, keeping the body firm so that it can
bend and extend without breaking (1,2,3). Although segmented
worms may appear simple, the organs inside them are highly
developed; various annelids have organs that can sense touch,
balance, and chemicals in their environment, and some even have
eyes with lenses (2,3). While all annelids share some important
physical characteristics, they live all over the world in a huge
range of habitats on land and in the water (both freshwater and
marine), with varying die