Sea spiders are marine arthropods of the class Pycnogonida, hence they are also called pycnogonids. The class include the only now-living order Pantopoda, alongside a few fossil species which could trace back to the early or mid Paleozoic. They are cosmopolitan, found in oceans around the world. The over 1,300 known species have leg spans ranging from 1 mm (0.04 in) to over 70 cm (2.3 ft). Most are toward the smaller end of this range in relatively shallow depths; however, they can grow to be quite large in Antarctic and deep waters.
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, except for Pentanymphon antarcticum, which has five pairs, and Sexanymphon mirabilis, which has six pairs.
Nymphon is a genus of sea spiders in the family Nymphonidae. The species within this genus are all benthic organisms found in most major oceans across the globe from the littoral zones to the deep sea, with a strong distribution around polar regions: Arctic and Antarctic waters. Out of the sea spider genus, Nymphon is the most diverse with over 200 species had been described, with a majority of them being found in the Southern Ocean region. This genus may also contain bioluminescent species.
Pycnogonidae is a family of sea spiders.
Pycnogonum is a genus of sea spiders in the family Pycnogonidae. It is the type genus of the family.
Ammotheidae is the most diversified group of the class Pycnogonida, with 297 species described in more than 20 genera, of which only Nymphopsis and Sericosura were found to be monophyletic. Despite its internal taxonomic uncertainty, studies on 18S rRNA supports its monophyly, and the subdivision on Achelinae and Ammotheinae subfamilies.
Tanystylum is a genus of pycnogonids in the family Ammotheidae.
Nymphon gracile is a species of sea spider first described by William Elford Leach in 1863. The species highly resembles other members of the genus Nymphon, and species identification from morphological traits alone is, therefore, a complex task.
Colossendeis is a genus of sea spider belonging to the family Colossendeidae. These sea spiders are typically found in the deep sea. This genus includes the largest pycnogonids, with leg spans frequently ranging from 40 to 50 cm. The largest sea spider, Colossendeis colossea, can reach a leg span of 70 cm. This genus also includes some bioluminescent sea spiders.
Callipallene is a genus of sea spiders in the family Callipallenidae. There are more than 30 described species in Callipallene.
Haliestes is a genus of sea spider (pycnogonid) from the Silurian aged Coalbrookdale Formation of England. It contains a single species, Haliestes dasos. The species was first described by David Siveter et al. in 2004.
Palaeoisopus is a monotypic genus of fossil pycnogonid, known only by one species, Palaeoisopus problematicus, discovered from the Lower Devonian Hunsrück Slate of Germany. It have several characters unusual for a pycnogonid, such as swimming legs with alternating size, medially-arranged eyes, and most significantly, a long, segmented abdomen, which were highly reduced in modern counterparts.
Colossendeis colossea is a species of sea spider in the family Colossendeidae. The species was first described by Edmund B. Wilson in 1881. It is the largest pycnogonid species known to science, reaching a leg span of 70 cm (28 in). Body length, including proboscis and abdomen, can reach 7 cm (2.8 in).
Colossendeis acuta is a sea spider that occurs in deep-sea habitats in the Antarctic Pacific. The species shows sexual dimorphism and the eggs are brooded by the male.
Dodecolopoda is a monotypic genus of sea spider 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 and the first such species to be discovered.
Decolopoda is a genus of sea spider belonging to the family Colossendeidae. This genus includes two valid species, D. australis and D. qasimi. As the name of this genus implies, these two species are among the seven species of sea spider with five pairs of legs instead of the usual four leg pairs. The species D. australis is notable as the first polymerous sea spider to be discovered.
Flagellopantopus is an extinct genus of pycnogonid arthropod known from the lower Devonian aged Hunsrück Slate. A single species is currently known, Flagellopantopus blocki, which was described from the Emsian aged Kaub Formation in Germany.
Colossendeis megalonyx is a species of pycnogonids, also known as sea spiders, in the famly Colossendeidae. The species was first described by Dutch zoologist Dr. Paulus Peronius Cato Hoek after his voyage on the HMS Challenger from 1873-1876.
Pentapantopus is a genus of fossil pycnogonid. The only known species is Pentapantopus vogteli from the Hunsrück Slate of Germany. This sea spider was thought to have had five pairs of legs, however a 2024 study disproved this. It is recognizable by its flatten, tuberculated legs with the first pair having less segments than other sea spiders.
