For a Nearly Hundred-foot-long Jellyfish, It’s Christmas All Year

This Apolemia siphonophore (colonial jelly) was photographed by the Monterey Bay Aquarium Research Institute using an underwater robot about 3,400 feet below the surface of Monterey Bay. Photograph 2005 MBARI

Like the fuzzy tinsel used to deck Christmas trees, this jellyfish relative—known as Apolemia—looks soft enough to cuddle. But keep in mind that it’s also armed with tiny poison-filled needles, which it shoots into animals unfortunate enough to blunder into it.

Apolemia is part of a group called the siphonophores, which are related to jellyfish. The Portuguese Man-of-War is perhaps the most well known siphonophore.

In general, animals in this group are made up of one or more “bells,” which they use to propel themselves through the water. The bells are attached to a train of stomachs, from which hang thin tentacles coated with batteries of stinging cells. All of these parts are connected by one digestive tract.

Siphonphores can be anywhere from a few inches (centimeters) to over 100 feet (30 meters) long. Apolemia and another group, Praya, are so long that they’ve been known to show up on sonar.

These animals are ambush predators, lying in wait with their tentacles extended. When prey like small fish or tiny crustaceans brush against the tentacles, stinging cells fire, harpooning the prey. The tentacles contract, bringing the wriggling victim to a waiting stomach to be digested.

Some siphonophore species drift through the water with their tentacles hanging straight down from their body stalk—like a diaphanous curtain of death. Other species twist and curl themselves into shapes—like spirals or Js—in order to deploy their tentacles.

Certain species actively set their “nets” by swimming in certain directions. As a siphonophore swims, it can relax part of its body, enabling it to drag behind the rest of the animal. Think of pulling one end of a ball of yarn free from the rest.

As the siphonophore swims in a circle or spirals through the water, its body arranges itself into a J or some other formation behind it.

Gravity and currents can undo those shapes, so every now and then, the animal must gather its net and swim to another location to set its trap.

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Jane J. Lee is a news writer and editor at National Geographic.