Dracunculus medinensis or Guinea worm is a nematode that causes dracunculiasis, also known as guinea worm disease. The disease is caused by the large female nematode of D. medinensis, which is among the longest nematodes infecting humans. The adult female is primarily larger than the adult male. The longest adult female recorded was 800 mm (31 in), while the adult male was only 40 mm (1.6 in). (Wikipedia)
Some theories say, that the symbol rod of Asclepius is based on this worm.
Detail of a painting by Werner Horvath.