Sea spider

Sea spiders Temporal range: Late Cambrian–present PreꞒ Ꞓ O S D C P T J K Pg N
Left to right, top to bottom: Austrodecus bamberi (Austrodecidae), Colossendeis sp. (Colossendeidae), Pycnogonum stearnsi (Pycnogonidae), Ammothea hilgendorfi (Ammotheidae), Endeis flaccida (Endeinae), Nymphon signatum (Nymphonidae)
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Chelicerata
Class:	Pycnogonida Latreille, 1810
Order:	Pantopoda Gerstaecker, 1863
Type genus
Pycnogonum Brünnich, 1764
Families
See text.
Synonyms
Arachnopoda Dana, 1853

Sea spiders are marine arthropods of the order Pantopoda^[1] (lit. ‘all feet’^[2]), belonging to the class Pycnogonida,^[3] hence they are also called pycnogonids (/pɪkˈnɒɡənədz/;^[4] named after Pycnogonum, the type genus;^[5] with the suffix -id). 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).^[6] 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.

Although "sea spiders" are not true spiders, nor even arachnids, their traditional classification as chelicerates would place them closer to true spiders than to other well-known arthropod groups, such as insects or crustaceans, if correct. This is disputed, however, as genetic evidence suggests they may be a sister group to all other living arthropods.^[7][8]