Blue Button (Porpita porpita)

…a species of colonial porpitid hydrozoans which occur in tropical and sub-tropical waters of the Pacific, Atlantic, and Indian Oceans. Although blue buttons look similar to jellyfish they are actually a colony of numerous hydrozoan polyps. Blue buttons are typically seen drifting on the surface of the ocean where it feeds on zooplankton which drift too close. Blue button colonies consist of two main parts: the float which is a hard brown circle which keeps the colony afloat, and the colony which forms the “tentacles” of the organism, these tentacles are laced with nematocysts which are used to dispatch prey.  


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Images: Bruce Moravchik and Tanay PrabhuDesai

Awesome photograph of a Porpita porpita aka The Blue Button Jellyfish. Although looks similar to a jellyfish, each apparent individual is actually a colony of hydrozoan polyps. The blue button is a Chondrophore, which is a group of cnidarians. The chondrophores are similar to the better-known siphonophores, which includes the Portuguese Man o’ War.


Green Hydra (Hydra viridissima)

…is a species of freshwater hydroid found throughout the northern temperate zone. These microscopic medusans are commonly found in stagnant waters from spring to summer where they feed on passing animals with their stinging tentacles.



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“Freshwater Hydroid” (Cordylophora caspia)

…a ‘unique' species of Oceaniid hydrozoan which is native to Northern Europe, but has been introduced into the United States and Canada. True to its common name Cordylophora caspia inhabits freshwater and brackish (or sightly salty) habitats, with colonies growing on a myriad of hard surfaces like rocks, pilings, and even mussel shells. Like marine hydroids C. caspia is predatory and will consume a variety of freshwater invertebrates. 

Cordylophora caspia populations may benefit from the expansion of zebra and quagga mussels in North America, as they provide substrate. It is thought that the increase salinity in systems impacted by road salt benefit them as well. 


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Image: Nadine Rorem