40 Fun Facts About Flatworms

Which US president's surname is also a genus of leaf-shaped flatworms, named from Tupi words for 'leaf animal'?

Obama joins the Tupi words oba, leaf, and ma, animal, so the match with the 44th president is pure coincidence. One species, Obama nungara, has spread from South America to Europe.

Which mating duel do some large marine flatworms fight, with the loser left to carry the eggs?

Penis fencing can last up to an hour, as each worm tries to stab and inseminate its rival while dodging the same fate. The winner escapes the costly work of developing eggs.

A cut planarian flatworm regrew with a head at each end after five weeks aboard which orbiting laboratory?

The ISS carried the worm pieces for a Tufts University study, and one fragment came back double-headed. Electric fields can trigger the same oddity on Earth.

The green-banded broodsac flatworm pulses inside a snail's eye stalks, mimicking which prey to lure hungry birds?

Caterpillars are what the throbbing, striped sacs resemble, and the parasite also keeps its snail in brighter, higher spots. Birds have been seen tearing out only the sac, so the snail may live on.

The parasitic flatworm Ribeiroia ondatrae is blamed for which pond animals growing extra or missing hind legs?

Frogs pick up the larvae as tadpoles, when the parasites settle around the budding hind limbs. A deformed adult is easier for a heron or hawk to catch, which carries the worm to its final host.

Bipalium land flatworms carry tetrodotoxin, a nerve poison best known from which fish served as fugu in Japan?

Pufferfish made the poison infamous, but in 2014 two of these worm species became the first land invertebrates found to carry it.

Researcher James McConnell claimed in the 1960s that planarians could gain what by eating ground-up fellow worms?

Memories seemed to pass from trained worms to the cannibals that ate them, but other laboratories could not reliably repeat the result.

Most flatworms have no anus, so undigested food leaves the body through which part?

The mouth doubles as the exit, because most flatworms have no anus and simply regurgitate what they cannot digest. A few long species break the rule and have one or more.

The longest tapeworm known, which can stretch past 30 metres, lives in the gut of which sea animals?

Whales such as the sperm whale host Tetragonoporus calyptocephalus, whose body can run to 45,000 segments. It probably sheds billions of eggs in a lifetime.

Larvae of the tapeworm from which undercooked meat can lodge in the human brain and trigger seizures?

Pork tapeworm larvae that settle in the brain are among the commonest causes of seizures in developing countries. People catch that form by swallowing the worm's eggs, not by eating the meat.

Schistosomiasis, spread by blood flukes, ranks second only to which other parasitic disease in the tropics?

Malaria alone does more damage in the tropics than these worms, whose larvae bore into people who wade, wash or swim in infested fresh water.

Schistosome eggs have turned up in mummies from which country, where the blood fluke was first identified?

Egypt is where the worm was first described, in 1851, and its eggs have since been found in mummies about 3,000 years old.

Schistosomiasis is also known by which name, honouring the German doctor who found its worm during autopsies?

Bilharzia honours Theodor Bilharz, who spotted the worm in 1851 while working at a Cairo hospital. He died at 37 of a fever caught on an expedition.

The lancet liver fluke makes which infected insects climb grass blades each evening, to be eaten by grazing sheep?

Ants carrying the fluke clamp their jaws onto a grass tip at dusk and hang there until dawn, night after night, until a grazing animal swallows them.

The broad fish tapeworm can absorb most of the vitamin B12 in a person's food, leading to which blood condition?

Anaemia can follow because the worm takes around 80% of the B12 its human host eats. Averaging ten metres, it is the longest tapeworm found in people.

The New Zealand flatworm, an invasive pest in Britain and Ireland, feeds almost entirely on which soil animals?

Earthworms are almost its only food in Europe, which degrades the soil they keep healthy. At rest the flatworm coils up like a tiny Swiss roll.

The New Guinea flatworm was deliberately released on Pacific islands to control which crop-eating invader?

Giant African snail control backfired: the flatworm also devoured rare native snails and now ranks among the world's 100 worst invasive species.

Which structures, bundled into organs called protonephridia, act as a flatworm's simple kidneys?

Flame cells are named for the tuft of beating flagella inside each one, which flickers like a candle. They drive waste water out through tiny pores.

The word 'fluke' for a parasitic flatworm comes from the Old English name for which flat-bodied fish?

Flounder was 'floc' in Old English, and the leaf-shaped parasites were named for sharing its flattened, diamond-like outline.

The old flatworm class Turbellaria is named for tiny whirlpools the animals stir up using which structures?

Cilia, the microscopic beating hairs that coat the body, churn the water into the little whirlpools behind the name. Small species also swim with them.

Flatworms have no lungs, gills or blood vessels, so oxygen reaches their cells by which simple process?

Diffusion only works over tiny distances, which is why a flatworm has to be flat: no cell can sit far from the surface.

Adult tapeworms have no gut at all, so what do they use to soak up digested food inside a host?

Their skin, a living layer called the tegument, absorbs sugars and amino acids and also shields the worm from the host's digestive juices.

What do planarians mainly use their two cup-shaped eyespots to do?

Planarians avoid light, and their eyespots cannot form images: they only tell which direction the light is coming from. Cave-dwelling species are often eyeless.

A planarian eats through a muscular tube that extends from the middle of its underside; what is the tube called?

Pharynx is the name for the tube, and some land planarians use it to pour enzymes over their prey and then suck up the liquefied remains.

Two young Diplozoon paradoxum flatworms that meet on a fish's gills are famous for doing what for life?

Fusing together is the only way they can mature, and a larva that never finds a partner usually dies. The joined pair can live for several years.

Which rash do lake bathers get when the larvae of bird-infecting flatworms burrow into them by mistake?

Swimmer's itch flares because the larvae die as soon as they get in, and each raised spot marks a single parasite. They were hunting for a water bird.

People can catch the sheep liver fluke, Fasciola hepatica, by eating which raw salad plant?

Watercress grows in the wet ground where the fluke's young stages leave their host and form cysts on plants, waiting to be eaten.

The Chinese liver fluke, caught from raw freshwater fish, is officially classed as a cause of which illness?

Bile duct cancer is tied so firmly to the fluke that the international cancer research agency lists the worm as a group 1 carcinogen, its top category.

Hydatid disease comes from a tiny tapeworm whose eggs people usually pick up from which domestic animals?

Dogs carry the adult worm, barely 6 mm long, after eating infected sheep offal. In people its eggs grow into fluid-filled cysts that can last for years.

Which drug, on the WHO's list of essential medicines, is the standard treatment for schistosomiasis and tapeworms?

Praziquantel was developed in Germany by Bayer and Merck in the 1970s, and a single yearly dose is given to whole communities where schistosomes are common.

A tapeworm's body is a long chain of egg-producing segments, each one known by which name?

Proglottids each hold both male and female organs, so a single tapeworm can fertilise itself. Ripe ones break off and leave the host packed with eggs.

The oldest known tapeworm eggs, about 270 million years old, were found in the fossilised dung of which fish?

A shark left the droppings in the Permian period, and one of the eggs inside still holds a developing larva.

Which British television presenter deliberately infected himself with tapeworms and found that he gained weight?

Michael Mosley swallowed beef tapeworm cysts for a BBC documentary and put on weight, the opposite of what old tales of tapeworm slimming pills promise.

Which geneticist, later a Nobel winner for fruit-fly work, ran early systematic studies of planarian regrowth?

Thomas Hunt Morgan published a whole book on regeneration in 1901, years before the fly experiments that won him the 1933 Nobel Prize.

Which adult stem cells, making up about a fifth of a planarian's cells, let it regrow any lost part?

Neoblasts are so potent that transplanting a single one into a planarian dying from radiation has been shown to rescue the animal.

Biologists call flatworms acoelomates because they lack which internal feature that most complex animals have?

A body cavity, or coelom, surrounds the gut of most animals; in flatworms the same space is packed solid with tissue.

Unlike jellyfish, flatworms have a distinct head end and tail end, a body plan known by which term?

Bilateral symmetry gives an animal a front that meets the world first, which is why flatworms gather their nerves and sense organs at the head.

Which nickname do Bipalium land planarians, invasive in North America, owe to their wide head plates?

Hammerhead worms earn the name with a wide head plate, and the Latin Bipalium, from words for two and shovel, likens them to a pickaxe.

The tiny flatworm Gyrodactylus salaris, which clings to the outside of fish, has devastated which species in Norway?

Atlantic salmon suffer so badly that the worm is nicknamed the salmon killer. It gives birth to live young that already carry the next generation inside them.

A study in Argentina found planarians could curb which disease-carrying insects by eating their larvae?

Mosquitoes of two species were eaten at every larval stage, and the flatworms could live in the artificial containers where the insects breed.