This remarkable creature is a worm (Diplozoon paradoxum - the "paradoxical double animal"). It lives on the gills of carp-like fish and as a hermaphrodite it is theoretically capable of mating with itself. In the course of maturing two of these parasitic worms grow together in the middle of their bodies and become effective Siamese twins joined together until death. The vagina of each half of the hermaphrodite becomes permanently linked to the sperm duct of the other half. William Bolsche termed the beast "a love monstrosity, an erotic Briareus with four sexual organs mating crosswise in a double marriage." There is more to the sex-life of worms than some of us realise!