The sea spider family consists of over approximately 1,300 species!
These small animals live in many different parts of the world including Australia, New Zealand, the pacific coast of the US, to the Mediteranean, the Carribbean, to the north pole, and south pole.
They are most common in shallow waters, but can be found as deep as 7,000 metres, living in both marine and estuarine habitats. Pycnogonids are well camouflaged beneath the rocks and among the algae that are found along shorelines. They range in size from 1-10mm, to over 90cm in some deep water species.
‘Sea spiders’ are not true spiders or even arachnids. Sea spiders have long legs in contrast to a small body size. In total, pycnogonids have four to six pairs of legs for walking plus other appendages which often resemble legs. These are used for caring for young, cleaning, and courtship.
Because of their small size, slender body and legs, no respiratory system is necessary, with gases moving by diffusion. A proboscis allows them to suck nutrients from soft-bodied invertebrates while their digestive tract extends into the legs. Pycnogonids are so small that each of their tiny muscles consists of only one single cell surrounded by connective tissue.
Sea spiders either walk along the bottom with their stilt-like legs or swim just above it using an umbrella-like pulsing motion. Sea spiders are generally predators or scavengers. Only males care for laid eggs and young.
In 2007 remarkably well preserved fossils were exposed in fossil beds in south-eastern France. Researchers discovered about 70 fossils from three distinct species of sea spider which were around 160 million years old.