Facts: Siphonophores

Siphonophores are complex gelatinous marine animals in the phylum Cnidaria. This is the same phylum that true jellyfish belong to. However, unlike a jellyfish, a siphonophore is not classified as an individual organism. Each specimen is a colony of individual polyps and medusae called zooids that work together to function as one. The colony may be equipped with gas-filled floats or large swimming bells. Each zooid is specialized to perform a particular function for the colony. The zooids cannot survive alone. Most siphonophores are free swimming. Almost all live beneath the surface. Some can temporarily attach their tentacles to the substrate. They inhabit all oceans and many live in the deep sea. They are fragile and hard to study. Colonies come in different shapes and sizes. They rise and sink in the water column by swimming, changing the amount of gas in their floats, or both. Each colony very much looks like a single organism. The zooids in a colony can be differentiated by function. They may be responsible for swimming, defense, reproduction, and so on. Fishing polyps produce long stinging tentacles to catch prey. They may eat tiny crustaceans like copepods, along with fish, or even other siphonophores. Feeding polyps with shorter tentacles digest the prey. The different types of polyps occur together in groups, each called acormidium, along the main stem of the colony. Groups are added as the colony grows. Each colony is typically sectioned into two structural and functional parts. Most species have an upper stem portion called the nectozome. This is where the swimming bells are located. The nectozome supports and propels the colony. The lower stem portion is called the siphosome. This is where the colony members live, such as the feeding polyps and the stinging polyps. In addition, the float, called the nematophore for the species that possess one, is located at the top of the colony. Siphonophores belong to an order of about 175 species with three suborders that have slightly different body forms. The calicophorans have swimming bells, but lack a float. The physonects have a large float and swimming bells. The cystonects have a float, but no swimming bells. This suborder contains the best known siphonophore, the Portuguese man of war. This siphonophore remains at the surface. The modes of reproduction for siphonophores vary among different species and there is still much that is not fully understood. A fully grown siphonophore is asexual and does not become a sexually mature individual. Siphonophore colonies are formed from one original polyp through the process of budding. In general, the original polyp is hatched from an egg and forms the float or upper section of the siphonophore. Secondary polyps bud from the original polyp. Some species can build extra colony members only from a single budding zone, at the top of the stem. Other species may bud from numerous budding zones along the stem. In many species, the swimming bells are replaceable and will quickly regrow if lost. In other species, loss of the swimming bell is terminal. Typically, reproductive polyps create medusae that produce eggs and sperm. These medusae may remain attached to the colony and often provide propulsion. They release large quantities of eggs and sperm into the sea. Fertilization is by chance. Fertilized medusa eggs eventually hatch and grow into asexual adult siphonophores. Most species bud off both male and female members. However, in some species, each colony only buds off either one sex or the other. For example, the Portuguese man-of-war has separate sexes. The lifespan of siphonophores is poorly studied. It is possible that some species live 10 or more years. The likely largest ever recorded specimen was an estimated 150 ft long. Many species are bioluminescent and can emit light. One species can even emit red light instead of the usual blue or green. For more marine facts, click the SUBSCRIBE button!!