Three Portuguese-man-of-war, each about eight inches long, were discovered on Shoreham beach this morning (Saturday, October 14).
Coming into contact with a Portuguese-man-of-war can cause a reaction which in extremely rare cases can be fatal.
The discovery comes after several sightings of the creature were reported in West Sussex yesterday (Friday, October 16).
The jellyfish was spotted in Worthing by a dog walker, Angela Hawke, at Kingston Gorse Beach yesterday.
She said: “I alerted the council and they are informing the Beach Officers.
“Fortunately, my dog is fine.”
Eight of the creatures were also discovered washed up on nearby Sussex beach Bracklesham Bay in Chichester, prompting a warning from the district council for surfers and swimmers to take care.
Reports of Portuguese man-of-war near the Sussex coastline are very rare, but usually occur earlier in the year, a spokesman from Chichester District Council said.
There have been recent reports in places such as Cornwall and Wales, added the spokesman.
Anyone who spots a Portuguese man-of-war is advised to leave the water and report the sighting to the council.
A spokesman for the HM Coastguard in Littlehampton said: “If you see any jellyfish, but in particular these ones, don’t touch them.
“Even though they are out of the water they can still leave a very nasty sting so stay away and keep if you have a dog it may be best to keep them on a lead.”