Sea spiders, or pycnogonida, are a distant cousin of terrestrial spiders and can grow to over 50cm in leg span. They may be “abundant” and “abundantly large” in polar regions due to “deep-sea ...

I checked and it seems to be a member of the rare, marine arthropod, probably a member of the Pycnogonida. Its 'body' is very small and all of its internal organs are said to be in its legs.