Peachy keen, jellyfish

We're well accustomed to marine jellyfish, but sightings of freshwater jellyfish are also hitting the headlines, most recently in the US and Sri Lanka. Freshwater jellies, otherwise known as Craspedacusta sowerbyi, can be found in almost any calm waters and have made appearances on nearly all the continents.

Freshwater jellyfish, like their sea-dwelling brethren, start off life as minuscule larvae which attach themselves to hard surfaces like rocks or corals before turning into tiny polyps. These then reach the ephyra stage, during which the stalk of the polyp develops ridges, and grows in size. It now resembles a stack of dishes, and the top-most "plate" matures most quickly, eventually detaching itself. This floats off and becomes a medusa, at which stage which we recognise it as a jellyfish. (You can look as some great pictures of developing freshwater jellies here.) Craspedacusta sowerbyi usually only peak at a diameter of about three centimetres, making their translucent bodies easy to miss in the water.

Easier to pronounce is their alternative name, peach blossom fish, which better evokes the floral patterning on these jellies. These jellyfish are commonly found in China, where it is said that they float to the water's surface during the blossom season.

Legend has it that the 1st century Chinese beauty, Wang Zhaojun, wept as she floated away from her home on a dragon boat, and her tears became jellyfish. This romantic origin makes the peach blossom fish desirable pets and there have been moves to prevent people from scooping these little fellas up and keeping them in the home. And rightly so: peach blossom fish are better left in their home environment as they can be crucial indicators about water quality. (Not to mention the fact that they'd much rather be swirling among the fallen blossoms than in a jar on top of your mantlepiece.)