Surprise! Baby Sea Anemone Has One Venom, Adult Has Another

Little starlets get eaten by one set of predators, adults by a different set, and they also need to hunt, explain Hebrew University scientists on unexpected discovery of morphing venom

The sea anemone Nematostella: Picture shows the body and tentacles of the lovely cnidarian in dark blue seawater.
Yaara Columbus-Shenkar / Hebrew University

Cnidarians are so much more than mere blobs of swimming gook with tentacles. The latest revelation is that one of them, the starlet sea anemone, develops startlingly different forms of toxin for the different stages of its life: As a “baby” it has one venom to avoid getting eaten; as an adult, it makes different venom in order to hunt.

This factoid could be of more than academic interest one day. Not a few medicines are based on natural poisons, including from primitive animals like the cnidarians. There could be a whole raft of molecules science hadn’t known about, the researchers hopefully suggest.

The discovery of the venom metamorphosis in the starlet, known to science as Nematostella, was reported Monday in eLife Science by a collaboration of researchers from the Hebrew University of Jerusalem, the Indian Institute of Science and the University of North Carolina at Charlotte.

Though science hadn’t expected anything of the kind, it makes sense, Prof. Yehu Moran of the Hebrew University told Haaretz. The Nematostella larva is microscopic, while the adult is a few millimeters long. They have dramatically different sizes and lifestyles and needs (larva and adult are also preyed on by completely different predators). It stands to reason they would evolve different venoms to deal with the different situations.

To be clear, scientists had assumed a venomous animal is armed with the same toxin throughout life. Nematostella is the first life-form for which the morphing venom has been proven.

“There were hints that it might happen in other animals, such as comb snails, a predator that lives in the ocean, and possibly in baby snakes. But if baby snakes have different toxins from adults, the difference is subtle,” Moran explains. The difference between baby and adult Nematostella venoms is not subtle at all.

In other words, if you’re stung by a baby Nematostella, a larva or an adult, the effect on you will be very different. If you’re a fish.

Humans don’t notice their sting, Moran says, which is one of the reasons they research the Nematostella as opposed to other cnidarians. Another reason was that, unusually for a cnidarian, Nematostella can be grown in the lab throughout its life cycle.

Under the wing of Mother’s venom

Sea anemones are cousins of jellyfish and coral. All belong to the cnidarians, which are the oldest extant form of venomous animal.

There are three types of Nematostella. One, the Polaris, was last seen in 1921, in the vicinity of the North Pole. Moran says they “work on the common type, Nematostella vectensis” – aka the starlet sea anemone, which is indigenous to estuarine waters around North America. The starlet is also commonly used in researching regeneration. (Common is relative, of course: the starlet is considered a threatened species.)

The starlet sea anemone begins life as a fertilized egg, which hatches into a larva, which does not eat – it just floats around or gets eaten. At some point, the larva anchors and develops into an adult, which is a stationary polyp that stings fish and arthropods with its tentacles, incapacitating them. Then it devours them.

The unfertilized egg is dormant. “It can’t produce a thing. But around it are the mother’s cells, which confer its toxic properties,” explains Moran. The anemone mothers spit the unfertilized, envenomed eggs out of their mouths into the water, where they are fertilized by sperm spat out of the mouths of the father.

From the moment the egg is fertilized and starts to develop, it starts to generate its own toxins, says Moran.

Our baby Nematostella isn’t going to feed until it’s adult. Neither egg nor larva need poisons to hunt. They need a poison that renders them disgusting. Their venom causes predators to immediately spit them out if swallowed.

Not to be nitpicky, but if it doesn’t “poison” them, is the "disgusting" substance the larva is producing a true venom?

Yes and no. Moran helpfully defines venom as anything that impairs the natural physiology of another animal, pointing out that with a lot of things that disgust us, if we swallow them, bad things will happen.

So if we are a fish and swallow this larva, will bad things happen? We aren’t sure. Also, the pure definition of venom requires administration through a lesion, which doesn’t happen here. But we can say that the starlet larva thoroughly deters predators.

As the larva matures into an adult, it starts producing profoundly different toxins that help it kill and eat other animals.

The lab also demonstrated that the adult starlet has one type of toxin-producing cell by its mouth, which poisons fish and crustaceans, and other types of toxin-producing cells along its body, to dismay predators.

Unlike our Nematostella, some sea anemones can deliver a painful sting. If you’re stung by a sea anemone and notice it, you may need to remove the sting from your extremity, wash the site and take a painkiller. In rare cases, hospitalization may be necessary. In contrast to popular wisdom, applying urine or shaving foam to the injury is not considered helpful, though vinegar may be.