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Illacme plenipes
Female Illacme plenipes (MIL0020) with 618 legs - ZooKeys-241-077-SP-6-left.jpg
A female I. plenipes with 618 legs
Scientific classification
I. plenipes
Binomial name
Illacme plenipes
Cook & Loomis, 1928
Niche-based distribution model for Illacme plenipes - ZooKeys-241-077-g001.jpeg
Predicted habitat suitability (maximum in blue) for I. plenipes based on climatic variables

Illacme plenipes is a siphonorhinid millipede found in the central region of the U.S. state of California. It has up to 750 legs, more than any other animal in the world. One of two known species in the genus Illacme, it was first seen in 1926, but was not rediscovered until 2005, almost 80 years after its discovery, by Paul Marek, then a Ph.D. student at East Carolina University and now at Virginia Tech. Marek published his discovery in the journal Nature.


Although no known millipede has one thousand legs, Illacme plenipes comes the closest with one recorded specimen having 750 legs. On average, they have over 600 legs, twice the average for millipede species. Despite having more legs than any other organism on Earth, it is relatively small-bodied among millipedes. Females grow to just over 3 cm; males are slightly smaller and have fewer legs.

Taxonomic history

The species was first discovered in San Benito County, part of the California Floristic Province, in 1926 by federal scientist Orator Cook and formally described by Cook and Harold F. Loomis in 1928. Cook and Loomis described the species without illustrations, and in 1996 Rowland Shelley of the North Carolina Museum of Natural Sciences re-examined specimens and redescribed the species. Marek and colleagues produced a more detailed description of the morphology of I. plenipes in 2012 and provided refined illustrations based on scanning electron micrography. The second species, Illacme tobini, was discovered and named in late October 2016 by Marek and colleagues.


Illacme is a member of the order Siphonophorida and family Siphonorhinidae. A second species of the genus, I. tobibni, was described in 2016. The closest relative of Illacme is undetermined, but a likely candidate is Nematozonium of South Africa which shares a long, narrow body shape and characteristics the gonopods.

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