* Japanese name: Yamanamekuji
* Scientific name: Incilaria fruhstorferi
* Description: Growing up to 20 cm long — bigger than a baby's arm — this is surely no slug, but a monster; a specter from a Hayao Miyazaki movie come to life. If you see one, be prepared to photograph it next to your hand, if you can bear to put your hand so close, for no one will believe you if you simply claim without evidence to have come across this giant shell-less gastropod mollusk. It is a mottled lump of "gristle," colored brown, beige and black, the gristle being mainly a muscular foot. On the top, behind the head, which has two pairs of tentacles, is the mantle — underneath this are the all-important genital opening and a hole for respiration, as well as the anus. The mouth is between the lower, smell-detecting tentacles (the upper tentacles are the eyes), and contains a radula, which is like a tongue with teeth. Both pairs of tentacles retract into the body when the animal hits an obstacle, or if you poke them gently with your finger.
* Where to find them: Slugs live all over Japan, in grassland, woodland and farmland, parks and gardens — where they are especially feared and loathed. Mountain slugs are more elusive than their garden cousins, and live at higher altitudes, in more rural areas, amid leaves, rocks and soil. They are sensitive to water conditions, and when there is little water they hide under rocks to preserve liquid.
* Food: Mainly decomposing matter from plants, but also from dead animals, even other dead slugs: the mountain slug is not fussy. Fungus is also eaten, along with fruit and vegetables, making them an enemy of farmers and gardeners.
* Special features: If seeing one of these beasts alone is startling, be prepared in case you see two, especially in amorous embrace. Slugs produce mucus, which helps them glide over the ground and stops them falling down steep surfaces, but which is also used during copulation. The mountain slug is a hermaphrodite, having both male and female reproductive organs. To copulate, two slugs wrap themselves around each other and exchange both eggs and sperm. Sometimes, for good measure, one or both slugs will chew off the other's penis. This is done not for a tasty snack, but because the penis often gets stuck in the body of the receiving slug: eating it enables the slugs to disengage. A slug with its penis chewed off is no longer able to function as a hermaphrodite; it is now and forever a female. The mountain slug hibernates in dead logs over winter.