The blue button
Commonly known as the blue button, Porpita porpita is a marine organism. It occurs in tropical and sub-tropical waters of the Pacific, Atlantic, and Indian oceans. Superficially similar to a jellyfish, each apparent individual is in reality a colony of dozens hydrozoan polyps.
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, a single modified polyp, is round, almost flat, and about one inch wide. The hydroid colony, which can range from bright blue turquoise to yellow, resembles tentacles like those of a jellyfish. Each polyp has numerous branches, each of which ends in knobs of stinging cells called nematocysts. The colony has just one mouth, located beneath the float, which is used for both the intake of prey and the expulsion of wastes. The blue button has no means of propulsion and drifts wherever the winds and currents take it.
This isn't in fact the real thing, but rather a glass model made in the nineteenth century. In the 1880s father and son Leopold Blaschka (1822-1895) and Rudolf Blaschka (1857-1939) ran a small workshop in Dresden, Germany. Initially they made costume jewellery and glass eyes for taxidermists and the blind. However, about 1863 they started to make exquisite glass models of marine invertebrates and these soon became their main business. At their height they had salesmen working across Europe and North America and as far afield as Japan and India. By 1888 the Blaschka sales catalogue listed over 700 different models. Sea creatures are extremely difficult to preserve in their natural colourful state and thus the lifelike models were in great demand by museums and private collectors. The firm went on to make an extensive range of glass models of plants but when Rudolf died in 1939 there was no one to carry on the business and production ceased.
You can see a photograph of the real live creature here. Or, if you prefer a video take a look here.