Sea Spiders are not spiders in the traditional sense. They are known as pycnogonida or pantopoda.
All of them are carnivores and predators (for examble feeds on anemones, sponge, hydrozoa, mossanimals, molluscs and zoanthids).
Sea spiders are typically eigth legged.They are reproduce sexualy.
The photo shows a sea spider that is a predator on zoanthid corals. This species feeds on zoanthids and is a zoanthid pests.
A method is to physically remove the adults with some tweezers.
Ammothea hilgendorfi has 4 pairs of legs, the body consists of 4 segments. They live on sediments, mussel clumps, algae such as kelp, etc, can also be found on echinoderms, such sea cucumber and starfish.