The Box Medusa

The Box Medusa
Tamoya haplonema, photo by Mark Fisher.
The first time I ever saw a box jellyfish, I was twelve. Our father took us to the Monterey Bay Aquarium. I never forgot what he said... That it was the most deadly creature on earth. To me, it was just the most beautiful thing I'd ever seen.

~Will Smith, Seven Pounds

Medusa is the word for jellyfish in Greek, Finnish, Portuguese, Romanian, Hebrew, Serbian, Croatian, Spanish, French, Italian, Hungarian, Polish, Czech, Slovak, Russian, and Bulgarian (though most of us probably think of a mythological character with snakes on her head and a stony gaze, not a jellyfish). Jellies along with corals, man-of-wars, anemones, and others belong to the phylum Cnidaria, which comes from the Greek word "cnidos," meaning stinging creature. Touching one of the many cnidarians will make it clear how they got their name. These diverse animals are all armed with stinging cells called cnidocysts (also called nematocysts), and they are united based on the presumption that their cnidocysts have been inherited from a common ancestor.

Cnidarians have two distinct body plans: 1) polyp, which is sessile as an adult and 2) medusa, which is mobile. Some cnidarians, such as jellies, go through both body plans in their life cycles. Members of this phylum are essentially bags of mostly water. They consist of three layers. They outer ectoderm, or epidermis, houses the cnidocysts (the stinging cells). The inner endoderm, or gastrodermis, lines the gut. Between the two is the mesoglea, a layer of jelly-like substance. The mouth is often surrounded by a ring of tentacles. The nervous system responsible for tentacle movement, digestion, waste expulsion, etc. is composed of nerve cells scattered across the body, a nerve net (so no brains for these guys).

Food stuffs are obtained in generally one of two ways, the predator way and the plant way. Many cnidarians, such as jellies, use their cnidocysts to trap prey in their tentacles. Others, such as corals, rely on symbiotic dinoflagellates within their tissues; these single-celled creatures carry out photosynthesis and pass on the nutrients to their hosts. Corals are, essentially, photosynthetic animals.

There are four major groups of cnidarians: Anthozoa, which includes anemones, sea pens, and true corals; Hydrozoa, the most diverse group with fire corals, the Portuguese man-of-war, by-the-wind-sailors, etc; Scyphozoa, the true jellyfish; and Cubozoa, the amazing box jellies.

Class Anthozoa
Anthozoans are probably the most famous cnidarians. Corals are the builders of some of the richest and most complex ecosystems on the planet. Anthozoans also have a long and diverse fossil record, extending back at least 550 million years. The oldest anthozoan fossils are from the late Precambrian, though true corals of the kind living today did not appear until the middle Triassic, about the same time that the first dinosaurs were evolving.

Class Hydrozoa
Many hydrozoans are often confused for true corals or true jellyfish, but they are colonial organisms, composed of many individuals, each specialized for various functions. Most alternate between a polyp and medusa stage. Spending part of their lives as "jellyfish" is what makes them hard to distinguish from scyphozoans.

Class Scyphozoa
The true jellyfish. Scyphozoans include most of the jellies familiar to beach-goers. They are
1) free-swimming, 2) polymorphic, existing in several forms or color varieties, 3) dioecious, having the male and female reproductive organs in separate individuals, and 4) carnivorous. Their life cycle involves an alternation between the sessile polyp phase and a free-swimming medusa stage, though the medusa stage is usually dominant.

Class Cubozoa
Cubozoans prefer to live in warm, shallow, marine waters near the coast. They inhabit warm waters worldwide but are particularly known in Australia, Southeast Asia, Hawaii, and off the United States gulf and east coasts. A non-threatening species, Carybdea marsupialis, enters Southern California near Santa Barbara during warm weather. The most venomous species of this class, Chironex fleckerii, is found on the northern shore of Australia and on the coasts of New Guinea, Vietnam, and the Philippines. Good thing we don't have that guy around here!

In general, box jellies look a lot like true jellies, the scyphozoans. But it's not especially challenging to tell the two classes apart. Cubozoans have a square shape when viewed from above, hence the name. The other prominent difference is the tentacle arrangement. The bottom corners of a box jelly's bell each sport a muscular pad called a pedalium (plural pedalia). One or more tentacles attach to each pedalium, so box jellies have four evenly spaced tentacles, or tentacle bunches. Cubozoans are divided into orders depending on the number of tentacles attached to each pedalium.

On the bell, located midway between the pedalia, are four sensory structures called rhopalia. If you look close, inside the rhopalia, you'll see a remarkable thing looking back at you! Box jellies have eyes, and surprisingly complex ones at that. Whereas some jellies do have simple eyespots that distinguish between light and dark, box jellies are unique in the possession of true eyes, complete with retinas, corneas, and lenses, not so different from you or me. They also retain the simple eyespots, for bragging rights. It's unclear how the images seen are interpreted by box jellies since they have no brains, and few experiments have been performed to determine just how well they can see, but they can see well enough to avoid swimming into a pole. A box jelly can look both inward towards its mouth and outward since each rhopalium dangles on a muscular stalk. Also inside each rhopalium is an organ called a statocyst, which is sensitive to orientation, allowing the jelly to sense whether they are upside-down, sideways, or rightside-up.

Box jellies are active and agile swimmers. True jellies are often categorized as planktonic, meaning they can't swim strong enough to escape whatever currents they inhabit. Consequently, many true jellies wash up on beaches. However, box jellies are unusually strong swimmers (well, compared to most true jellies). Cubozoans (of various sizes) have commonly been observed to swim a 3.5 feet in five to ten seconds, though they can reportedly reach much faster speeds. Not only are box jellies quick, they are remarkably agile. Aided by their advanced eyesight, they have been reported maneuvering around the pilings of piers and fleeing would-be human collectors.

Perhaps partially due to their evasive maneuvers, it was not until about 1970 that the complete life cycle of a cubozoan was observed. Mating appears to occur once every year, sometimes in large aggregations. In one group of box jellies, the male puts his tentacles into the bell of the female and passes packets of sperm. Fertilization takes place inside the females. In all the other groups, males and females release sperm and eggs, respectively, into the water. Fertilization takes place in the water column. Each egg develops into a planula. Cubozoan planulae are pyriform (that's "pear-shaped" in scientific lingo). After a planula settles, it grows into a polyp and crawls around like an inchworm, budding off more polyps. Box jelly polyps do not closely resemble the polyps of true jellies. These differences may indicate that cubozoans have a separate evolutionary origin from scyphozoans. After a few months of feeding, each polyp metamorphoses into a single juvenile medusa, complete with four new tentacles and four rhopalia.

Not surprisingly, given their squishy nature, there have not been many fossil cubozoans discovered. Today, there are about twenty known species. The classification of Cubozoa within Cnidaria has been the subject of a great deal of debate. Classically, cubozoans were categorized as a subgroup of Scyphozoa, the true jellies. However, when it was observed that the cubozoan polyp and life cycle were rather different than those of scyphozoans, Cubozoa graduated to its own class.

There are three native species found in Gulf waters. Two of them are listed in the Texas Parks & Wildlife database: Chiropsalmus quadrumanus, the four-handed box jelly (locally known as "sea wasp" or the "hot jelly"), and Tamoya haplonema, one of the four-tentacled box jellies. The other native is Tripedalia cystophora, the mangrove box jelly. Several species of box jellies are referred to as sea wasps, but it's usually reserved for the aforementioned Chironex fleckerii, the most dangerous of the box jellies, not one found here.

The four-handed box jelly has been documented in at least four Texas estuaries, mostly in the Galveston Bay System, and also offshore in state waters. It is a colorless, transparent cubozoan with a bell diameter usually five to six inches, and length a little less. Bundles of seven to nine mauve tentacles dangle from each pedalium. They have a very irritating sting. It's found seasonally, August through October.

Tamoya haplonema has been documented at least twice in Texas waters, once in Corpus Christi Bay and once off shore near Port O'Connor, both times in very low numbers. The bell is tall and transparent with long, milky-yellow tentacles, one on each corner. The sting is painful, but not lethal.

The mangrove box jelly is one of the smaller species of box jellyfish, growing to the size of a silver dollar. It usually lives in large groups near the surface of the water where it can prey easily on small crustaceans. Unlike other box jellies, which are usually clear or whitish in color, the mangrove has color variations from greenish gray to brownish yellow. It has three tentacles on each corner. This species' sting seems to vary from absolutely nothing at all to a mild itch. While this box jelly's range does, occasionally, include the Gulf of Mexico, it hasn't actually been documented in state waters and is primarily a resident of Central America.

Fun Fact: there are over four-hundred vast marine dead zones worldwide that are too polluted for almost all higher life, but not for jellies! The number of global dead zones has doubled about every ten years since the 1960s. During the summer of 2008, the Gulf of Mexico's dead zone covered about 8,000 square miles, the size of Massachusetts. It is expected to soon reach about 10,000 square miles.

Out of all cnidarians, cubozoans are the most venomous. Box jellies are known as the suckerpunch of the sea, not only because of their powerfully painful venom, but also because they are almost transparent. Only a few species in the class have been confirmed to be involved in human deaths, and some species pose no serious threat, though few species of box jellies are only weakly venomous. The tentacles are used to catch prey (fish and small invertebrates) and for defense from predators, including butterfish, batfish, rabbitfish, crabs, and various species of sea turtles. Sea turtles, however, are apparently unaffected by the sting and eat box jellies indifferently.

Each tentacle is lined with thousands of cnidocysts, the hallmark of cnidarians. Each cnidocyst houses a coiled, envenomed barb. When a tentacle comes in contact with chemicals on either prey or predator, the barb uncoils and fires, injecting the venom, a venom that is distinct from that of scyphozoans.

Box jellies produce a unique family of toxic proteins. However, the venom is complex and difficult to collect, so is incompletely understood. Though they are structurally similar, the venoms vary a bit between species, indicated by the broad range of species-specific effects. Most have components which can cause local pain and necrosis, and in high doses, some contain components that can affect heart function and breathing.

The harm caused by a sting is dependent on a few factors: 1) the amount of skin contacted by cnidocysts; if more than ten percent of the total skin area of a person is covered with discharging tentacles, that can become life threatening, especially in children; 2) where contact is made; the chest has more serious implications than the foot; 3) the species of box jelly; 4) the size of the person; small children are more susceptible to stings than adults; and 5) the individual reaction of the person; people who are allergic to the venom are, of course, in more danger when stung. Antivenom is available for box jelly stings.

Acetic acid, found in vinegar, disables the cnidocysts that have not yet fired (though it will not alleviate the pain). Common practice is to apply generous amounts of vinegar prior to and after the tentacle is removed. To remove the tentacles, use a stick, towel, credit card, anything but your bare hands. Tentacles will still sting if separated from the bell, even after the creature is dead. Removing the tentacles before applying vinegar can cause unfired cnidocysts to come into contact with the skin and fire, resulting in more stings.

Although commonly recommended in folklore and even some papers on sting treatment, there is no scientific evidence that urine, ammonia, sodium bicarbonate, boric acid, lemon juice, fresh water, steroid cream, alcohol, papaya, or hydrogen peroxide will prevent further stinging from box jellies, and some of these substances even cause more venom to be released. Alcohol of any form should never be used for jelly stings, box or otherwise.

Eye stings should be rinsed with a commercial saline solution, such as Artifical Tears. Also, dab the skin AROUND the eyes with a towel that has been soaked in vinegar. Do not place vinegar directly in the eyes! Mouth stings should be treated with a vinegar mixture: one part vinegar to three parts water. Gargle and SPIT OUT the solution. Do not drink or swallow!

Or you could just do what the savvy Aussies do – wear women's pantyhose when you head out to the beach. Apparently, nylon prevents the jellies from stinging since it's a barrier to the chemicals on your skin.


Where I learned about box jellies, and you can too!

*Special thanks to Allen Collins, of the Smithsonian National Museum of Natural History, for catching some errors, post printing.

Venomous and Poisonous Marine Animals: A Medical and Biological Handbook
Edited by John A. Williamson, Joseph W. Burnett, Peter J. Fenner, Jacqueline F. Rifkin

Gulf States Marine Fisheries Commission:

National Science Foundation:

United States Dept of Agriculture:

Encyclopedia of Life:

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Lamar University:

Open Water Pedia:

University of California Museum of Paleontology:

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James Cook University:




CSL Antivenom Handbook: