''Gonionemus'' is a genus of

hydrozoan Hydrozoa (hydrozoans; ) are a taxonomic class of individually very small, predatory animals, some solitary and some colonial, most of which inhabit saline water. The colonies of the colonial species can be large, and in some cases the specialized ...

s that uses adhesive discs near the middle of each tentacle to attach to

eelgrass Eelgrass is a common name for several plants and may refer to: * ''Zostera'', marine eelgrass * ''Vallisneria ''Vallisneria'' (named in honor of Antonio Vallisneri) is a genus of freshwater aquatic plant, commonly called eelgrass, tape grass o ...

sea lettuce The sea lettuces comprise the genus ''Ulva'', a group of edible green algae that is widely distributed along the coasts of the world's oceans. The type species within the genus ''Ulva'' is ''Ulva lactuca'', wikt:lactuca, ''lactuca'' being Latin ...

, or various types of

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

instead of swimming. They are small (bell diameter to 25 mm) and hard to see when hanging onto swaying seaweed. Nevertheless, they are capable of swimming when necessary. The bell is transparent, revealing the four orange to yellowish-tan

gonad A gonad, sex gland, or reproductive gland is a mixed gland that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, produces sper ...

s that lie along most of the length of the four radial canals. The pale yellow

manubrium The sternum or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major blood vessels from injury. Sha ...

has four short, frilly lips. Up to 80

tentacle In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work main ...

s line the bell margin, with about an equal number of

statocyst The statocyst is a balance sensory receptor present in some aquatic invertebrates, including bivalves, cnidarians, ctenophorans, echinoderms, cephalopods, and crustaceans. A similar structure is also found in ''Xenoturbella''. The statocyst cons ...

Copepod Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (inhabiting sea waters), some are benthos, benthic (living on the ocean floor) ...

s are a favored prey. This marine hydrozoan is common in warmer waters. The conspicuous stage in the dimorphic lifecycle is the small medusa. The polypoid stage is present as a tiny, solitary polyp which feeds on protozoans and other small plants and animals. The polyp stage closely resembles ''Hydra''. The medusae are active swimmers that propel themselves upward in the water column by rhythmic pulsations of the bell. Upon reaching the surface, the bell relaxes, the tentacles become fully extended, and any small fish or crustaceans encountered as the medusae slowly drift toward the bottom are ensnared. Occasionally, the medusae use their adhesive pads to attach to seaweed or other objects near the bottom, extend their tentacles, and wait for prey to bump into them. The manubrium hangs down from the center of the subrellum. It bears the cross-shaped mouth and the four short oral lobes which grip the food. Digestion begins in the center of the manubrium, which communicates with the four radial canals and the ring canal. The velum is well-developed and used in swimming. Having a velum is characteristic of the hydrozoan medusae. The gonads are four yellowish structures embedded in the surface of the epidermis beneath the radial canals. The ovaries are more granular in appearance than the testes (sexes are separate). The gametes are shed into the sea, and the zygotes develop into ciliated planular larvae which grow into minute polyps. These polyps can bud off other polyps or medusae. The tentacles of the medusae are hollow and connected to the exumbrellar surface by a tentacular bulb where cnidoblasts are formed.

Species

*'' Gonionemus agilis'' Watson & Govindarajan, 2017 *'' Gonionemus hamatus'' Kramp, 1965 *''

Gonionemus vertens ''Gonionemus vertens'', the clinging jellyfish, is a small species of hydrozoan in the family Olindiidae found in coastal regions throughout large parts of the Northern Hemisphere. Description and behavior The appearance of ''Gonionemus vertens' ...

'' A. Agassiz, 1862

References

Olindiidae Hydrozoan genera {{Hydrozoa-stub