Giant deep-sea spider spotted crawling on ocean floor near Antarctica

Researchers suspect species grows so large partly due to cold temperatures of their environment

Scientists have filmed a giant deep-sea spider crawling on the Southern Ocean floor, shedding more light on the diversity of underwater arachnids.

Researchers from the Schmidt Ocean Institute noticed the sea spider, the size of a dinner plate, about 2km beneath the icy surface waters of the South Sandwich Islands, a chain of volcanic islands near Antarctica.

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 gigantism”, a phenomenon of several deep-sea animals growing larger than their shallow-water relatives.

Species that exhibit deep-sea gigantism include the colossal squid, the big red jellyfish, the deepwater stingray, and the blob octopus.

Sea spider imaged at 1,122m below sea level (NOAA)

Scientists theorise that these species grow so big because cold temperatures of their environment favour slow metabolism.

“Immense pressure and frigid temperatures, while insurmountable obstacles to land lovers like humans, allow some animals to have very slow metabolisms and the ability to reach gargantuan proportions,” the Schmidt Ocean Institute explained in a post on Facebook.

The increased buoyancy of the ocean also allows deep-dwelling organisms to defy gravity and grow larger compared to their land-based cousins, researchers say.

“The buoyancy of ocean life means they don’t have to work against gravity, and it is this that allows many of them to grow to such immense sizes without collapsing under their own weight,” the institute explained.

The inaccessibility of deep-sea environments for even advanced underwater vehicles, however, has hindered the study of such creatures.

Scientists have discovered nearly 1,500 species of sea spiders so far and classified them into the order “Pantapoda”, which means “all legs” according to the US National Oceanic and Atmospheric Administration.

They are not all legs, though, and have additional appendages. They lack lungs and breathe through their exoskeleton and don’t bite, scientists say.

They feed by sucking on the insides of soft-body marine life forms like jellies and sea anemones using a tubular part of their body called a proboscis.

Sea spider species range from infinitesimally small to as large as an adult human face or a moderately-sized serving platter, researchers say.