The attached video of a green ribbon worm filmed in Penghu, Taiwan by a fisherman Wei Cheng Jian has gone viral and been called bizarre and horrific. Although the ribbon worm or nemertea may be considered ugly and has some unusual characteristics, like all creatures it has a role in the circle of life on planet earth.
The ribbon worm may be maligned due to its probing proboscis that looks like another pink worm crawling out of it or a giant pink tongue, but it is really searching out food. Some types have a sticky proboscis, some have suckers to grasp their prey, some have a sharp spike called a stylet for repeated stabbings. The proboscis can also be used for burrowing in sand or mud.
The worm’s oozing green slime appearance is kind of creepy. Ribbon worms produce that slippery mucus covering their bodies as an aid in navigating through mud and rocks on ocean floors. Scientists have trouble catching them because the mucus makes them so slippery. They also use body muscles to locomote and cilia on their epidermis along with the mucus from gland cells helps them move and glide.
They usually live worldwide under the sea at all ocean depths, in freshwater, or among rocks, but they sometimes are found on cold, wet land areas and mud flats. As their mucus dries out, they need seawater as a lubricant or they will die.
Although the smallest are less than a centimeter long and look like thread, the length of some can make them scary too. The bootlace nemertean, Lineus longissimus, in the North Sea may be the longest animal on earth, found at 180 feet long in the U.K. in 1864. Hard to measure because when threatened they can shrink to one tenth of their length, they are believed to grow to 197 feet. Even longer than a blue whale, they remain less than an inch in circumference.
Ribbon worms can be herbivores or carnivorous and although some have a poison to stun their prey, they are not dangerous to humans. When a ribbon worm is unable to find food, it is able to digest 95 percent of its own body.
Overpopulation of the ribbon worm could become a problem. It has the ability to regenerate lost or damaged parts of its body and uses replacements it reserves in internal pouches. The Ramphogordius sanguineus is so exceptional at this that one worm only 6 inches (15 centimeters) long can regrow over 200,000 worms.
Not much has been proven to eat a ribbon worm other than other nemerteans, but it does provide food for some spot and croaker fish. In one two decade study, nemerteans were found in 276 out of 85,454 fish. Four were found in the guts of 2,183 short-fin squid, 1 in 50 green crabs guts, and all polychaetes, crabs, lobsters, and hermit crabs rejected them as food. Three bird types feed on nemerteans, the black-bellied plover, the semipalmated plover, and the herring gull all fairly common on the west coast.
Some species might be considered a threat by creatures whose food supply is crustaceans and mollusks. The Carcinonemertes genus ribbon worms live as parasites on crabs and eat the crabs’ eggs. The Malacobdella live parasitically in mollusks’ mantle cavities on food filtered by their hosts.
Another species pops up from the sand as a fiddler crab walks over, uses its proboscis to cover the victim with toxic slime, paralyzing the crab. The ribbon worm slides into a crack in the shell and eats the crab from the inside out. Also able to easily expand better than pythons, some species can swallow whole prey more than double their body width including other kinds of worms, fish, crustaceans, snails and clams.