Monotypic Chelicerata genera

Pentanymphon is a monotypic genus of sea spider (class Pycnogonida) in the family Nymphonidae. The only species in this genus is Pentanymphon antarcticum. As the name of this genus suggests, this genus is among the four genera of sea spiders with five pairs of legs in adults instead of the usual four leg pairs. The species P. antarcticum was the second polymerous (i.e., extra-legged) sea spider to be discovered.

Dodecolopoda is a monotypic genus of sea spider (class Pycnogonida) in the family Colossendeidae. The only species in this genus is Dodecolopoda mawsoni. This species is notable as one of only two species of sea spider with six pairs of legs in adults (instead of the usual four leg pairs) and the first such species to be discovered.

Sexanymphon is a monotypic genus of sea spider (class Pycnogonida) in the family Nymphonidae. The only species in this genus is Sexanymphon mirabilis. As the name of this genus implies, sea spiders in this genus feature six pairs of legs in adults instead of the usual four leg pairs. The species S. mirabilis is notable as one of only two species of sea spiders with six leg pairs. This species is found in the Southern Ocean.