Range: Cosmopolitan

Size: Average less than 8 inches (20cm) in length but may be the longest animals alive

Diet: Small invertebrates, invertebrate eggs, molluscs, fish, and other ribbon worms

Lifespan: Unknown (Eighteen months recorded in one species)

Transcript:

Today on Animal Fact Files we’re discussing ribbon worms. Originally, these worms were believed to be closely related to flatworms. Like flatworms, ribbon worms can regenerate lost parts of their bodies, but today it's thought ribbon worms are more closely related to segmented worms, like earthworms, as well as molluscs. Ribbon worms, however, are unsegmented. What sets them apart from other worm-like animals is the presence of a proboscis. Ribbon worms get their common name because they have flattened bodies when they push out their proboscis. They look like a ribbon! Another common name for the ribbon worm is the proboscis worm. Their proboscis is a noodle-like appendage. They keep their proboscis tucked inside their body until it’s needed. Some have a sharp stylet which they can use to pierce prey and defend themselves. Others use their proboscis like a lasso to trap prey. Terrestrial ribbon worms use their proboscis to move! This tool may be as long as the ribbon worm itself! These invertebrates average less than 8 inches (20cm) in length with some species only reaching about the width of your fingernail at max size. On rare occasions, however, they can be very, very long! So long, in fact, that when stretched out they’re longer than a blue whale! The longest ribbon worm recorded is believed to have been 177 feet (54m) in length making it the longest animal known so far!

These animals are cosmopolitan: they live throughout the world. A majority of ribbon worms are marine creatures. They live from the intertidal zone to the ocean's depths spending their time on the seafloor. There are, however, also freshwater ribbon worms and even terrestrial ribbon worms that live alongside water edges. Some species can be found with other animals like sponges and tunicates. These species grab food particles as these filter feeding animals create water currents. Others are parasitic to crustaceans. Some ribbon worms seek out meals in the form of small invertebrates, invertebrate eggs, molluscs, fish, and other ribbon worms! Though they're soft-bodied, ribbon worms aren't easily taken by predators. Some produce toxins and some fight off threats with their proboscis. When they are eaten, however, their predators include birds like gulls and sandpipers, crustaceans, and each other.

Most ribbon worms are born either male or female, but some start off as a male and develop female sexual characteristics later in life. Some are born with both male and female reproductive organs. Their styles of reproduction can vary. Some are asexual and reproduce clones of themselves from broken fragments of their bodies. Others form mating knots where multiple individuals gather together and release their gametes all at once. Some species lay eggs in the environment, others retain their eggs which develop inside the mother until they hatch and are born live. Some emerge as small versions of the adults while others hatch as larvae that develop later in life. With over a thousand species to account for, ribbon worms are diverse! Speaking of which, these animals come in different colors. Some are bright, others are dull. Some change colors throughout the year. For example, males may become brighter during breeding season. In species that have separate sexes, the females are often larger than the males. It's unknown how long ribbon worms live in the wild, though one species has been recorded at living 18 months.

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