The ribbon worm is any member of the phylum Nemertea. Over 900 Nemertea species exist including free-living forms as well as parasites of sea squirts, crustaceans, and mollusks. Most Nemertea are found in marine habitats, but some may live on land (terrestrial) or in freshwater. There are 13 known terrestrial ribbon worm species worldwide. Four species exist in Australia (Argonemertes: australiensis; dendyi; hillii; stocki) and they are from the Argonemertes genus. Land-dwelling nemerteans need dark, damp, and cool habitats to live. They can be found under rotting logs, in leaf litter or under large rocks or stones. They are typically found in lands where the climate is calm and damp.
Ribbon worms, also called proboscis worm, bootlace worm, nemertean, or nemertine, have muscular reversible (able to be turned inside out) proboscis (tubular feeding and sucking organ), housed in a fluid-filled enclosure above the belly or gut. This area is used to trap prey and it is used for burrowing. Land-dwelling ribbon worms may use it for fast movement. At a minimum of 8 inches long, the ribbon worms body is long and lean with finlike appendages. Some giant ribbon worm species or ‘Lineus longissimus’ may reach up to 100 feet long.
Ribbon worms have several other unique abilities and traits. Some may have separate male and female organs (dioecious) while others may have both male and female organs (hermaphroditic). Ribbon worms can regenerate chopped or damaged parts of their body. In fact, ribbon worms may break up into pieces on their own and the pieces will grow into new worms.
Ribbon worms reproduce annually. Fertilization occurs externally, and the eggs and sperm are released separately. Ribbon worms develop by either the direct method or ciliated larval stage. The direct method does not include a larval stage and the ciliated larval stage is either a free-swimming larva called the pilidum or the Desor’s larva, which is similar to an adult. The larvae transform into ribbon worms in several days to several weeks after swimming among plankton.
According to Encyclopedia Britannica, www.britannica.com:
In general, ribbon worms are regarded as a distinct phylum at the highest point of acoelomate (without a body cavity) development; however, some evidence suggests that one proboscis cavity, or rhynchocoel, may be a true coelom. The important features used to classify the ribbon worms include the position of the brain relative to the mouth, the presence or absence of a stylet (or stylets) on the proboscis, and the position of the lateral nerves relative to the muscle layers.
For pictures or video of the giant ribbon worm or if you would like to see an average size ribbon worm in action, visit: http://www.seawater.no/fauna/slimormer/kjempe.htm or http://www.flickr.com/photos/pokerchampdaniel/3136421527/.