Invertebrates
Antarctic Sea Spider
Colossendeis megalonyx · also called giant sea spider
Growing far larger than its warm-water relatives, an Antarctic sea spider moves slowly across the Southern Ocean seafloor on impossibly long legs, its oversized body plan made possible by how easily oxygen dissolves in the cold water around it.
Overview
The Antarctic sea spider, Colossendeis megalonyx, is a Least Concern invertebrate native to ocean and polar habitat across the seafloor surrounding Antarctica and nearby subantarctic waters. Its unusually large size relative to warmer-water relatives, its highly reduced body plan, and its ability to breathe directly through its skin make it one of the more striking examples of polar gigantism found anywhere in the Southern Ocean.
Bigger simply because the water allows it
While sea spiders elsewhere in the world remain small and inconspicuous, the Antarctic sea spider has grown dramatically larger, a change scientists link directly to the unusually high oxygen levels dissolved in cold Southern Ocean water rather than any change in lifestyle.
Status
Least Concern, remaining widespread across suitable Southern Ocean seafloor habitat, with no significant conservation concerns currently documented.
Antarctic Sea Spider: common questions
Why does the Antarctic sea spider grow so large?
This species' unusually large size is thought to be linked to how efficiently oxygen dissolves in cold Southern Ocean water, an example of polar gigantism seen across several Antarctic invertebrate groups.
How does the Antarctic sea spider breathe?
This species lacks dedicated gills or lungs, instead absorbing oxygen directly through its thin body surface and long legs, an adaptation made possible by its extremely reduced body size relative to its legs.
What does the Antarctic sea spider eat?
This species feeds on soft-bodied invertebrates such as sea anemones and sponges, using a specialised feeding tube to extract soft tissue directly from its prey.
How fast does the Antarctic sea spider move?
This species moves slowly across the Antarctic seafloor on its long legs, rarely swimming and instead relying on a deliberate, methodical gait to get around.