Sealife guideSea spiders: fascinating creatures of the oceanThe marine arthropods

Last updated on 09/02/2025 at 12:22 AM

Pycnogonids are marine arthropods commonly known as sea spiders. These marine arthropods are related, on one hand, to spiders, typically with eight legs and on the other hand, to crabs, with a hard exoskeleton.

A sea spider carrying eggs in the waters of the Philippines © Francesco Ricciardi | Dreamstime.com

Sea spiders range in size from a few hundredths of an inch up to roughly 20 inches across the leg span for the largest species, often found in polar regions.

Sea spider species living in the cold waters of the Antarctic and Arctic oceans tend to be larger than their tropical counterparts adapted to warm waters.

Diet

Sea spiders feed on soft-bodied animals such as sea anemones, soft corals, sponges, nudibranchs, jellyfish and marine worms.

Reproduction

Sea spiders are an ovigerous species, meaning that once the eggs are fertilized, they are carried under the abdomen using a dedicated pair of legs to ensure their oxygenation by seawater.

Did you know ?

There are more than 1,300 species in this class !

About 20% of known sea spider species live in the Antarctic ocean.

In sea spiders, it is the male, not the female, that carries the eggs under his abdomen until they hatch.

The giant sea spider (Colossendeis megalonyx) is a massive Antarctic species whose legs can span over 24 inches, making it one of the largest sea spiders known.

In sea spiders, it is the male, not the female, who carries the eggs under his abdomen © Francesco Ricciardi | Dreamstime.com

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