“Worm” is our common word for invertebrate animals that have soft, elongated bodies. When most people think of worms, they usually think of nightcrawlers or red wigglers. Both may be called earthworms since they both are found in the earth, but they live very different lives.
Nightcrawlers are soil-dwellers. They like to burrow several feet below the surface. Red wigglers, on the other hand, are surface-dwellers and prefer to live within the top 6 inches of the soil. Red wigglers are often found among the fallen leaves, as well as in manure piles.
Worms – not just found on land
Not only do we find worms on land, but the ocean is full of them. Some of these marine worms resemble earthworms, but others look more like ribbons, flowers, peanuts, or even Christmas trees. Some marine worms are so small, you need a microscope to see them. Others are super long. Marine worms comprise several phyla, a grouping of worm members who share a general body plan.
Types of marine worms
Segmented worms include the oligochaetes (say “oh-LIG-oh-keets”), or worms with few bristles, such as the earthworm. In marine environments, polychaetes (this one’s easy — just think of a girl named Polly Keets) are much more common than oligochaetes.
Polychaete worms have many bristles. In fact, the name polychaete means “many bristles,” and one of the common names for polychaete is bristle worm. There are about 8,000 polychaete worm species worldwide — including my favorite, the Christmas tree worm, which as its name implies resembles a Christmas tree. While some polychaetes live in burrows or tubes, others move about freely.
Flatworms have many marine species, with very simple, flat bodies. They usually crawl on the bottom or along underwater surfaces, but they can swim. When they do, they do so with a dainty fluttering motion. Around coral reefs, they can be brightly colored, often with beautiful patterning. In bays and estuaries, they tend to be beige or brown.
Ribbon worms are unsegmented like flatworms, but their internal structure is far more complicated. They are usually much longer too. Like flatworms, ribbon worms can be brightly colored. The longest, the bootlace ribbon worm, is found on British seashores and can grow to be 100 feet long.
Peanut worms are also unsegmented. They tend to occur in shallow waters and burrow in soft sediments. Peanut worms get their name because when disturbed they contract into a lumpy peanut-shell shape. I find these sometimes when I pull my research gear in after it’s been deployed for some time. They must not be happy with me, because they’re always peanut-shaped.
Worms are important
Worms are an important part of the food chain in marine habitats. Some are filter feeders. They wave their sticky tentacles in the water to capture tiny microscopic food particles. Others are deposit feeders. They feed on sand and mud and get their nutrition from microorganisms contained in these sediments. Still others feed on seaweed, prey on other animals, or scavenge on dead animals.
Marine worms are also food for other marine animals, including many of our sport and commercial fish. They perform an important role in the marine environment. By breaking down and cycling nutrients between the sediments and surface waters, they help to keep our marine environments healthy.