Polychaetes - (‘poly’ = many, ‘chaeta’ = bristle) worms

What are they?

Animals are categorised into about 40 phyla (singular = phylum). All vertebrates (including all fish, bird, reptile, amphibian, and mammal species) are only one part of a single phylum called Chordata.  Sponges are their own phylum.  Corals, anemones, and jellyfish are another (Cnidaria).  Sea urchins, sea cucumbers, sea stars, and brittle stars are another (Echinodermata).  Shrimp, lobsters, bumble bees, and cockroaches belong to a huge phylum (Arthropoda), and so on.  People commonly call many things without a backbone (most animals on the planet) that are somewhat sausage shaped a worm. A 'worm' can then be any animal from about 10 different phyla! 

Polychaetes belong to the phylum Annelida (ringed or segmented worms) along with oligochaetes (like earthworms) and leaches.  Polychaetes are annelids that have flappy extensions (parapodia or 'feet') on each segment that help them swim, crawl, breathe, etc.  These parapodia have chaetae -bristles- in a remarkable variety of shapes and functions.  Some are harpoon shaped and help defend the worm while others may help them swim.  Tubeworms have chaetae that act like the emergency brakes on a runaway lift, locking them into their tubes when a hungry fish tries to pull them out. There are over 50 polychaete families and thousands of species living everywhere in the ocean in beaches and tidepools, drifting in the plankton, all the way down to the deepest hydrothermal vents. 

There are many species of polychaetes that have not been named or described yet so the world needs more wormguys and wormladies!