Chelicerata families

Nymphonidae is a family of sea spiders which has representatives in all the oceans. This family contains some 250 species, most of which are found in the genus Nymphon. Nymphonid bodies are between 1 and 15 mm long, the extent between the points of the legs reaching 150 mm. Most species are predators of hydroids. Like most sea spiders, species in this family have four pairs of legs in adults, except for Pentanymphon antarcticum, which has five pairs, and Sexanymphon mirabilis, which has six pairs.

Pycnogonidae is a family of sea spiders. This family includes two genera, Pycnogonum and Pentapycnon. This family is distributed worldwide.

Colossendeidae is a family of sea spiders (class Pycnogonida). This family includes more than 100 species distributed among six genera. These sea spiders inhabit the deep sea mostly but are also found in shallower waters, especially in Antarctic and Arctic waters.

Ammotheidae is a family of sea spiders. It is the most diverse sea spider family, with 297 species described in more than 20 genera, of which only Nymphopsis and Sericosura have been found to be monophyletic. Despite this internal taxonomic uncertainty, studies of 18S rRNA support the monophyly of the family, and its subdivision into two subfamilies, Achelinae and Ammotheinae.

Austrodecidae is a family of sea spiders. Austrodecids tend to be small measuring only 1–2 mm, characterized by an annulated proboscis with vertical slit-like mouth opening. It is the most basal family of the order Pantopoda, representing a lineage (Stiripasterida) sister to all other pantopod families (Eupantopodida).

Phoxichilidiidae is a family of sea spiders. About 150 species are described, almost all in the genus Anoplodactylus Wilson, 1878.

Callipallenidae is a family of sea spiders.