St John's jellyfish

Lucernariopsis cruxmelitensis


St John's jellyfish (Lucernariopsis cruxmelitensis) © Steve Trewhella

St John's jellyfish is a stalked jellyfish. These are closely related to anemones, free-floating jellyfish, and corals, all of which have stinging tentacles to paralyse or kill their prey and to protect themselves from predators.

This stalked jellyfish is the smallest member of its family.  Even at its largest, it does not quite reach 1cm in height. It lives on rocky shores that are exposed to moderately strong waves and currents, and is found close to the low tide mark or in shallow water.  Unlike other stalked jellyfish, it is rarely attached to seagrass but is often found on small, red seaweeds, such as Irish moss.

In appearance, it resembles an upside-down jellyfish, with its translucent bell underneath and tentacles on the top.  There are eight webbed arms within the maroon bell, with up to 35 rounded tentacles at the end of each.


European distribution

The UK distribution of the St John's jellyfish appears to be limited to the south-west of England, from Swanage in Dorset to north Devon, and the Atlantic coasts of Ireland.  It may occur in the wider north-east Atlantic.


Conservation status/need

  • St John's Jellyfish FactThis is a UK BAP Priority Species (BAP species are now Species of Principal Importance/Priority Species).
  • Species of principal importance for the purpose of conservation of biodiversity under the Natural Environment and Rural Communities Act 2006 in England.


Further information

Marine Life Information Network

World Register of Marine Species

JNCC - UK BAP Priority Species and Habitats