The strange way of 'taking care of children' of giant sea spiders

Giant Antarctic sea spiders have different biological characteristics from regular sea spiders, and their way of giving birth and incubating eggs is also very different .

The icy waters of Antarctica hide a mysterious ecosystem. There, with their tiny, spindly legs, strange sea spiders cross the seabed looking for a place to nest.

Giant Antarctic sea spiders have very long legs and can be up to 70cm. (Photo: R. Robbins).

For many years, scientists have been trying to understand how the giant Antarctic sea spider (Colossendeis megalonyx) gives birth. Finally, researchers found the answer and published this information in the journal Ecology last March.

Called sea spider but not spider

Marine ecologist Amy Moran at the University of Hawaii (USA), a member of the research team, said that most commonly seen sea spiders raise their young by carrying them around while they develop.

This species is distributed everywhere. They are found in different environments around the world, from deep water to shallow water, from waters with different salinities and temperature ranges.

Compared to other animals, our understanding of sea spiders is still quite small. But in general, their reproductive characteristics are still quite clear.

Specifically, after a pair of spiders decides to mate, the male climbs on top of the female and lines up the genital holes on her legs. The female releases eggs for the male to fertilize externally. The male will then hide the eggs in "special legs" called ovigers for incubation and care.

Giant Antarctic sea spiders are arthropods. (Photo: S. Rupp).

But with giant Antarctic sea spiders, no one has ever seen how they give birth and raise babies, even though 140 years ago, the scientific community did some research on this species.

Called sea spiders, giant Antarctic sea spiders are not spiders, nor are they crustaceans like spider crabs. They are marine arthropods and are classified in a separate group called pantopods.

Strange way of "taking care of children".

In 2021, Ms. Amy Moran and her colleagues went to Antarctica to conduct a study on the phenomenon known as the "polar giant". This phenomenon refers to the fact that many species living in polar regions are much larger in size than their related species.

Sea spiders are no exception. Normally, sea spiders are just smaller than a fingernail. But at the poles, the stride of this species can reach 70 cm.

While diving under the ice in McMurdo Sound, some members of the research team encountered giant Antarctic sea spiders mating. So they gently moved these animals into observation tanks to learn how they reproduce.

Giant Antarctic sea spider eggs and larvae at each stage from incubation to hatching. (Photo: Moran).

Through observing two groups of spiders during the breeding season, the research team discovered that this species can create thousands of eggs and place them around a single spider.

A male spider will take these eggs and carefully "stick" them to the bottom of the tank. There, the eggs develop for several months and then hatch into spider larvae. It takes up to 8 months after birth for the larvae to hatch.

After observing in the tank, the research team repeatedly found similar clusters of eggs surrounding adult sea spiders in the natural environment.

Thereby, the research team concluded that giant Antarctic sea spiders have a different way of reproduction than other sea spiders. Instead of hiding eggs in ovigers, this species hides eggs in rocks on the seabed to take care of them.

Incubation time is also a mystery, not only for giant Antarctic sea spiders but also for some other sea spiders.

To date, scientists still do not understand why giant Antarctic sea spiders do not incubate eggs like other sea spiders. They speculate that the timing of egg application may have something to do with this.

When incubating eggs in the natural environment, giant Antarctic sea spiders will hide the eggs under a layer of seaweed for several weeks . This may also be the reason why no one has ever found eggs of this species.

In addition, hiding eggs under algae will also be a safer option. The reason is that the legs of giant Antarctic sea spiders are weaker than the legs of other sea spiders . If you place the egg nest in the father spider's legs, these eggs will not be safe.