It's a buoy! It’s a piece of plastic! It’s a… Portuguese Man o’ War!
Most Creighton students have heard of this species before and will likely recall images of blue, balloon-like structures attached to pasta reminiscent of a Brandeis meal. Popular conceptions of Physalia physalis place the species as a jellyfish, but it is actually a species of siphonophore! Siphonophores are colonies of genetically identical individuals called zooids that perform distinct functions to survive. These siphonophores are mostly found in tropical and subtropical seas, such as the Atlantic, Pacific, and Indian Oceans as well as the Sargasso and Caribbean seas.
The species Physalia physalis is one of the most prominent animals within the order of Siphonophora. Siphonophora contains around 175 hydrozoans, all of which are made up of colonies of zooids or polyps which perform specialized tasks to survive together. They are found in the phylum Cnidaria, which are primarily ocean-dwelling creatures. The main distinguishing feature of cnidarian species is the presence of cnidae. Cnidae, or nematocysts, are the stinging cells used to capture prey. There are two possible species of Man o’ War: P. physalis and P. utriculus. The species are distinguished by the presence of several large tentacles or a unique main tentacle, respectively. P. utriculus, also known as a Bluebottle or Indo-Pacific Man o’ War, is found in Australian waters and is smaller and not as venomous as the Portuguese Man o’ War. Below you can find the phylogenetic tree of Physalia physalis.
Physalia physalis is made up of four diverse zooids. One kind of zooid, the pneumatophore, is the balloon-like structure that the Portuguese Man o’ War is named after. Its fan-shape resembles a Portuguese warship at full sail. A specialized gland inside produces gases that expand the pneumatophore and allow it to float. It is thought that the alignment of the sail relative to the wind (left or right handedness) is established during early development. Since movement is primarily due to wind directions, it is hypothesized that left-handed colonies are more prevalent in the Northern Hemisphere due to prevailing winds, whereas right-handed colonies are dominant in the Southern Hemisphere. When threatened from above, the pneumatophore can also temporarily deflate in order to submerge further into the water.
Examples of both right and left-handed Physalia in the picture. Try to find both!
Nematocysts are what we typically think of first when we think of Physalia. These comprise the majority of the dactylozooids, which come in two distinct sizes for different types of food. These grow upon a tentacular palpon, attached just below the gastrozooids. The tentacles extend an average of 30 feet, but some specimens have been observed up to 165 feet in length. The nematocysts upon contact with another organism release a projection with hooks, barbs, and spikes that pierce the organism and inject paralyzing toxins. The stingers produce enough force to puncture a surgical glove! Although it is rarely fatal to humans, it is not a pleasant experience to be stung. Researchers of Physalia suffered tremendously at the terrible tentacles of Physalia: “In connection with our study of the venom contained in the capsule we undertook to prepare a large sample of isolated nematocysts, processing many hundreds of living Physalia. Consequently surfaces in the laboratory became contaminated with undischarged nematocysts. For weeks thereafter we suffered reminders of our carelessness whenever we touched water faucets, bench surfaces or laboratory aprons.”
Ouch! Stinging cells are just one part of the process of procuring food. After capturing prey, gastrozooids begin the digestive process. Gastrozooids are found on the underside of the pneumatophore, where several individuals can envelop food (plankton, small fish and squid, larval stages of crustaceans) by opening their writhing mouths in concert. The gastrozooids then secrete proteolytic enzymes from their mouths to digest food extracellularly. The digested food products are subsequently released into the main gastric cavity to be distributed to the remainder of the colony.
Physalia is dioecious, meaning that there are female and male colonies. The gonozooids, our fourth and final kind of zooid, organize themselves into gonodendra, which are reproductive structures that detach from a colony when fully developed. A gonodendron bears male or female gametes, a palpon for digestion, and a nectophore for slight locomotion. Once the gonodendron leaves the colony behind, the nectophore propels the gonodendron through the water column. Unfortunately, released mature gonodendra have not been observed; therefore, we know very little about how fertilization occurs. However, we know that the gonodendron descends the water column, releases its gametes to be fertilized, and that colonies only resurface when they reach a certain size.
Although the specifics are not known about the embryonic and larval development of the Physalia physalis, the predicted life cycle is shown above.
The Portuguese Man o’ War is a fascinating species that goes with the flow. Did you know that many animals harvest the stinging tentacles? Glaucus atlanticus, a nudibranch, feeds on Physalia and stores the stinging nematocysts as defense against predators. Immature Tremoctopus violaceus octopods carry Physalia tentacles for defense as well as to help capture prey. The Portuguese Man o’ War even have a symbiotic relationship with the species Nomeus gronovii, or “Portuegese Man o’ War fish". These fish are immune to the stinging tentacles and take shelter under the Portuguese Man o’ War for protection. If you are mesmerized by this incredible species and want to learn more, stay tuned to this blog! We guarantee that there is more to uncover about this mysterious species!
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