Nemertea is a phylum of invertebrate animals also known as Ribbon worms. They are also known as Proboscis worms because they can extend a proboscis to capture their food. There are about 1,400 species of ribbon worms nearly all of which are found in oceans around the world. Most species live on or in the sea floor, with many species found in brackish water in estuaries, and even some freshwater and land-based species. Their habitats include - in and among seaweeds, rocks, mussel and barnacle beds, under shells or buried in mud, sand, or gravel substrates.

They have a similar appearance to flatworms although they usually are larger, thicker-bodied, and longer. The largest species may grow to several metres or more but some species are less than 20 cm in length, and some just five millimetres long. Most species are pale, some are brightly coloured with patterns of yellow, orange, red and green.

Purple ribbon worm
Image © Gary McDonald Flickr

Nemertea have long, thin, unsegmented bodies. They have no true head and have an eversible (can be turned inside out) proboscis which is used for catching prey. They have a digestive system which includes a mouth, oesophagus, stomach, intestine and anus.

Most nemerteans are carnivores and predators, although some are scavengers and others are herbivores. They catch their prey with their proboscis which is wrapped around the prey which is then stabbed until it is dead. In some species the proboscis has a sharp part attached (a stylet). In some species the stylet contains a poison to kill prey faster.

Mot species have males and females which release sperm and eggs into the water. Only some species produce larvae, the majority produce offspring which resemble the adults.

Pink ribbon worm
Image © Eunice Khoo Flickr

References

http://en.wikipedia.org/wiki/Nemertea
www.reefed.edu.au/home/explorer/animals/marine_invertebrates/ribbon_worms
www.reefed.edu.au/home/explorer/animals/marine_invertebrates/ribbon_worms/nemerteans