Although this article is about jellyfish around the world, not specifically about the Caribbean, I know that most of my Caribbean friends and colleagues have had many an encounter with these magical beings. One unforgettable memory: snorkeling in a sea-within-a-sea (a swarm? a bloom?) of purple-flowered moon jellies off Boquerón Bay, Puerto Rico. [I will always be grateful to Augusto (Tuto) Ortiz for teaching us how to swim with jellyfish without getting stung.] Along with rhinoceroses, crows, and starfish, jellyfish are among my favorite creatures so, bear with me.

Here are excerpts from Elizabeth Kolbert’s “Scary, Squishy, Brainless, Beautiful: Inside the World of Jellyfish,” which includes fascinating information and amazing photos by David Liittschwager. [Elizabeth Kolbert is the author of book The Sixth Extinction, which won a Pulitzer Prize. David Liittschwager, “the Richard Avedon of obscure but beautiful creatures,” has shot 13 features for the National Geographic.] See full article at National Geographic.  

Scary, squishy, cool, brainless, mesmerizing—jellyfish are all of these and a whole lot more. Anatomically they’re relatively simple animals; they lack not just brains, but also blood and bones, and possess only rudimentary sense organs. Despite their name, jellyfish aren’t, of course, fish. In fact they aren’t any one thing.

Many of the creatures lumped together as jellyfish are no more closely related than, say, horseflies are to horses. Not only do they occupy disparate branches of the animal family tree, but they also live in different habitats; some like the ocean surface, others the depths, and a few prefer freshwater. What unites them is that they’ve converged on a similarly successful strategy for floating through life: Their bodies are gelatinous.

Not surprisingly, given their diverse evolutionary history, jellies exhibit a fantastic range of shapes, sizes, and behaviors. When it comes to reproduction, they’re some of the most versatile creatures on the planet. Jellyfish can produce offspring both sexually and asexually; depending on the species, they may be able to create copies of themselves by dividing in two, or laying down little pods of cells, or spinning off tiny snowflake-shaped clones in a process known as strobilation. Most astonishing of all, some jellies seem able to reproduce from beyond the grave.

The so-called immortal jellyfish resembles a tiny, hairy thimble and lives in the Mediterranean Sea and also off Japan. Members of the species can reverse the aging process so that instead of expiring, they reconstitute themselves as juveniles. The juvenile then starts the jellyfish’s life cycle all over again. It’s as if a frog, say, were to revert to a tadpole or a butterfly to a caterpillar. Scientists call the near-miraculous process transdifferentiation.

Moon jellies and their cousins, which include lion’s mane jellies and sea nettles, are known as true jellies. They belong to the class Scyphozoa, in the phylum Cnidaria, which also includes corals. (A phylum is such a broad taxonomic category that humans, fish, snakes, frogs, and all other animals with a backbone belong to the same one—the chordates—as do salps, which are sometimes lumped with jellies.) As adults, true jellies are shaped like upside-down saucers or billowing parachutes. They propel themselves through the water by contracting the muscles of their bells, and their tentacles are equipped with stinging cells that shoot out tiny barbed tubes to harpoon floating prey. To reel it into their mouths, they use streamer-like appendages known as oral arms. In some species the oral arms have mouths of their own.

Jellyfish like the dreaded Portuguese man-of-war are also related to corals, but they’re part of a different subgroup, the siphonophores, which practice an unusual form of collective living. What looks like a single man-of-war is technically a colony that developed from the same embryo. Instead of simply growing larger, the embryo sprouts new “bodies,” which take on different functions. Some develop into tentacles, for example; others become reproductive organs. [. . .]

For full article, see https://www.nationalgeographic.com/magazine/2018/10/jellyfish-species-reproduction-feeding-ocean/