Nematodes - The Round WormsSo you've got your segmented worms and your flat worms. There are more worms out there called nematodes. Nematodes are also called round worms. You might not know (but now you do) that there are more roundworms in the world than any other creature (we are referring to multicellular creatures). They are small and they are all over the place. If you are having problems imagining that, remember that there is an entire bottom of the ocean where insects and fish can't live. Guess who can?
Good to Have a GutWe like telling you what makes each type of animal special. Nematodes are also special. While you may see a small smooth worm, scientists see creatures that have a gut that is complete. Mouth, lips, gut, and a hole when basic digestion is done. That's pretty neat (if you're into nematodes). That complete gut was one of the first steps to organizing physiological systems. It is one step up from organisms that only have tissues.
Did We Mention They Are Round?They do not have specialized circulatory systems like annelids. And guess what... They are round! You knew that. Nematodes are round and have bilateral symmetry (both halves look the same). They also have special muscles that move down the length of that entire round body. Annelids (segmented worms) are different in that their muscles just work in each segment.
All Around You... And In YouWhere do you find them? We should say... Where don't you find them? Nematodes act like predators, hunting down other creatures. They are parasites, surviving at the expense of a host. The best example of nematodes as parasites is a disease called Trichinosis. Some are also herbivores, eating plant material and algae. How do they get so many places? It helps that so many species of nematode are very small. You need a microscope to see most of them.
Nature’s Glowing Slime (Scripps Oceanographic Inst. Video)
Encyclopædia Britannica (Nematodes):