Porpita porpita, commonly known as the blue button, is a marine organism consisting of a colony of hydroids found in tropical waters from California to the tropical Pacific, the Atlantic and Indian oceans. It is often mistaken for a jellyfish, but although jellyfish and the blue buttons are part of the same phylum (Cnidaria), the blue button is part of the class Hydrozoa.
The blue button lives on the surface of the sea and consists of two main parts: the float and the hydroid colony. The hard golden-brown float is round, almost flat, and is about one inch wide. The hydroid colony, which can range from bright blue turquoise to yellow, resembles tentacles like those of the jellyfish. Each strand has numerous branchlets, each of which ends in knobs of stinging cells called nematocysts. The blue button sting is not powerful but may cause irritation if it comes in contact with human skin.
It plays a role in the food web, as its size makes it easy prey for several organisms. The blue button itself is a passive drifter, meaning that is feeds on both living and dead organisms that come in contact with it. It competes with other drifters for food and mainly feeds off of small fish, eggs, and zooplankton. The blue button has a single mouth located beneath the float which is used for both the intake of nutrients as well as the expulsion of wastes.
It is preyed on by Glaucus atlanticus (common names sea swallow, blue glaucus) and Violet sea-snails of the genus Janthina.
Facts | Photo © Kathryn G.