Mauve stinger

A small mushroom-shaped jellyfish, usually 3 to 10 cm across the bell, coloured warm mauve, pink or purple-brown and covered in raised warty clusters of stinging cells that give the bell a rough, freckled look. Eight long, hair-fine marginal tentacles trail from the bell rim and can stretch a metre or more, and four thicker frilled oral arms hang below the centre. Everything about it stings, bell included, which is unusual - most jellyfish only sting with the tentacles.

It has no bottom-living polyp stage at all. The entire life cycle happens in open water, which is why it can appear in enormous numbers after a run of calm, dry weather and then be pushed inshore in a single night by an onshore wind. The species name noctiluca means night light: disturbed animals glow a faint blue-green in the dark.

In the Maltese islands this is the jellyfish - the most abundant species recorded by the long-running Spot the Jellyfish citizen-science campaign, and the one behind most of the swimmers' stings reported each year. Peak abundance tends to fall in late winter and spring, roughly February to April, with swarms possible at any time of year and especially after settled, windless spells. Maltese has no separate word for it; brama simply means jellyfish.