Sea Spiders Breathe Through Pores in Their Legs

sea spider, breathing — Sea spiders occupy marine habitats the world over, in both deep and shallow waters. But until now, scientists were not able to pinpoint the mechanism that allows them to breathe underwater in the absence of lungs or gills. Bret Tobalske/University of Montana

You can find a sea spider living in marine habitats all over the world, from shallow waters to the deep sea. They have the same eight legs you'd expect from land spiders, and like most species of spiders, sea spiders have segmented bodies and protective exoskeletons made of chitin.

Fossil records show that sea spiders have existed for hundreds of millions of years, boasting an ancient lineage within the world of marine invertebrates. Let's dive a little deeper.

What Do Sea Spiders Look Like?

These marine arthropods span a wide range of sizes. Some are minuscule, with a leg span of only 0.4 inches (1 centimeter). The largest sea spider species are found closer to the North and South Poles, and they can have a leg span of up to 28 inches (70 centimeters).

Their trunks are small in contrast to their long, multi-jointed, stilt-like legs, which house many of their vital organs. In fact, their genitals and most of their digestive system are encased in these delicate legs.

Sea spider hearts are also so weak that they rely on their digestive systems to circulate blood. And, one more fun fact: Male sea spiders carry the young, not females!

How Do Sea Spiders Breathe Underwater?

Most sea creatures have gills (like fish and lobsters) or lungs (like whales). Yet, sea spiders have neither gills nor lungs.

A study, published in the March 28, 2018 issue of the "Journal of Experimental Biology," has gotten to the bottom of how sea spiders move oxygen through their bodies by studying several species of giant Antarctic sea spiders.

The research team found sea spiders take oxygen into their bodies through hundreds of tiny pores in their cuticle, the tough outer skin that gives them structure and protection.

They put giant Antarctic sea spiders in respiration chambers to see exactly how much oxygen they were absorbing, and they found they were taking in enough through tiny holes all over their legs to run their entire bodies.

What Do Sea Spiders Eat?

Sea spiders primarily feed on soft-bodied animals such as sea anemones, worms and jellies. They'll also nibble on soft corals.

When they eat, they use their specialized tube-like mouths, or proboscis, to suck out nutrients.