may not be a complete list:
Ammotheidae
Austrodecidae
Callipallenidae
Colossendeidae
Nymphonidae
Phoxichilidiidae
Pycnogonidae
Rhynchothoracidae
Endeididae

Sea spiders, also called Pantopoda or pycnogonids, are marine arthropods of class Pycnogonida. They are cosmopolitan, found especially in the Mediterranean and Caribbean Seas and the Arctic and Antarctic Oceans. There are approximately 1,000 known species, ranging in size from 1-10 mm to over 90 cm in deepwater species: most are toward the smaller end of this range.

The correct taxonomy within the group is uncertain, and it appears that no agreed list of orders exists. Accordingly, families are listed in the table at the right. Furthermore, the evolutionary lineage of the sea spider group as a whole is disputed: their fossil record is sketchy at best, with the three earliest known genera originating in the Devonian. Some believe (or once believed) sea spiders to be among the chelicerates, together with horseshoe crabs, true spiders, mites, ticks and scorpions. While sharing many morphological features with the other chelicerates, major differences (such as their unique proboscis) have caused some taxonomists to remove sea spiders from this grouping.

Their reduced body size is in contrast to large, long legs, which may be present in four or more pairs. Because of their small size and slender body and legs, no respiratory system is needed for gas diffusion . A proboscis allows them to suck nutrients from soft bodied invertebrates, and their digestive tract has branches extending into their legs, known as diverticulae.

Their habitats range from the shallow intertidal zones to deepwater benthic environments, some 7,000 metres down. Sea spiders do not swim but rather walk along the bottom with their stilt-like legs. Most are carnivorous and feed on cnidarians, hydroids , sponges, soft corals, polychaetes and bryozoans.

External links

• Introduction to the Pycnogonida
• Sea Spiders (Pycnogonida or Pantopoda) Web Page
• Taxonomic hierarchy for the class Pycnogonida
• Images of Pycnogonida

• Images of Pycnogonida, and Pycnogonids in literature