Annelids live in soil-, freshwater, and oceans including Antarctic
seas. They may be striped or spotted, and pink, brown, or
purple in color. Others are iridescent or luminescent. Some have
colorful gills and cirri, modified parapodia. The endangered
Australian earthworm Megascolides, which is 3 m in length, is
the largest species; the smallest annelid is only 0.5 mm.
Active predation or scavenging is the feeding mode for most
annelids. Many annelids burrow incessantly, turning over and
exposing detritus and soil and aerating anaerobic muds and
sands; these activities are known as bioturbation. Swimming
annelids catch fish eggs or larvae. Filter-feeding marine annelids
capture bacteria and feed selectively on sediment particles
within tubes (which they build of mucus-cemented sand grains,
calcium carbonate, protein and polysaccharide compounds, and
other materials) buried in sand or mud. Some trap plankton on
a mucus-covered, ciliated eversible proboscis. Others pop out of
their tubes to seize prey. Certain species harvest algae growing
on their tubes. The sea star Luidia (A-34) hosts the polychaete
Podarke among its tube feet. Some carnivorous polychaetes have
fangs with which they inject toxins into prey.