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

Discover marine arthropods

Coconut crab
(Birgus latro)

Haig's Porcelain Crab
(Porcellanella haigae)

Heart crab
(Phyllolithodes papillosus)

Pink ghost crab
(Ocypode ryderi)

Purple shore crab
(Hemigrapsus nudus)

Red hermit crab
(Dardanus calidus)

Spotted cleaning shrimp
(Periclimenes yucatanicus)

Velvet swimming crab
(Necora puber)

Our latestUpdates

Friday, November 28th 2025

Disney Hollywood Studios, from Star Wars to Toy Story

Dive into the magical world of Disney's Hollywood Studios: Star Wars and Toy Story attractions and shows for the whole family.

Wednesday, November 19th 2025

Tenerife island

Tenerife, the largest of the Canary islands, is a volcanic gem in the Atlantic ocean. It boasts an incredible variety of landscapes, from golden or black sand beaches to the subtropical forests of the Anaga mountains and the majestic Teide volcano, Spain's highest peak. With its picturesque villages, rich local culture and countless outdoor activities, Tenerife is a perfect destination for every type of traveler.

Saturday, November 15th 2025

Batz island

Located in the English Channel off the northern coast of Brittany, just a few kilometers from the town of Roscoff, Batz island is a true little haven of peace where you can enjoy its wild landscapes, unspoiled beaches and historical heritage.

Photo of the Day

Rouget barbet doré
(Parupeneus cyclostomus)