It's great to put a name to the jellies we've seen, though we might not be able to pronounce most of the names (haha).
[Update on 26 Aug: Dr Dawson suggest some corrections after having a look at this blog entry. Thanks once again!]
[Update: First off, Dr Dawson points out that in jellyfish, 'tentacles' refers to stuff that is stuck to the edge of the bell. The other things that stick out from under the bell around the mouth are more properly called 'oral arms'. These terms have been amended in the entry below.]
The jellyfish above with orange oral arms and the white one below are both Chrysaora sp., Class Scyphozoa. Highly seasonal, when seen, many are seen on both the Northern and Southern shores. And then none seen again for some time.
The stings of these jellyfishes are very painful to humans. Chay Hoon got stung once during a dive and declared that she would rather hug a hydroid!
Elsewhere, the common names of these jellyfishes include Sea nettle (Nettle is a kind of stinging plant, so this name is a bit obtuse if you don't know the plant) and Compass jellyfish. Maybe it should just be called Ribbons of Fire Jellyfish or something equally more dire.
This may be Catostylus sp., Class Scyphozoa. We see this sometimes on Changi. As usual, when seen, usually in numbers and then none for a while.
From the Australian Museum's Wildlife of Sydney:
Catostylus mosaicus or Jelly Blubber is the most commonly encountered jellyfish along the Australian eastern coast and large swarms sometimes appear in estuarine waters. In Sydney waters, the Jelly Blubber's large bell is a creamy white or brown colour, but farther north it is usually blue. This is because the jellyfish has developed a symbiotic relationship with algal plant cells that are kept inside its body. These plants vary in colour from region to region. The algae photosynthesise, converting sunlight into energy that can be used by the jellyfish. The Jelly Blubber has no mouth but there are many tiny openings in its tentacles. The tentacles also have stinging cells that can capture tiny crustaceans and other plankton.[Update: Dr Dawson says "To my knowledge, there is currently no evidence that any species of Catostylus is photosymbiotic with zooxanthellae. So, the colour variation has a different cause (I don't know what it is)". ]
This jellyfish was bigger than my hand and is Cassiopea sp., Class Scyphozoa. Also known as the Upside-down jellyfish, it does indeed prefer to be upside down; usually found with oral arms facing upwards and bell facing the sea bottom. If you turn one the 'right' way up, it will slowly turn itself back upside down. They are quite commonly encountered on Pulau Semakau.
From the entry on Cassiopea on wikipedia:
Cassiopea is a genus of scyphozoan jellyfish very commonly found in shallow mangrove swamps, mudflats, and turtle grass flats in Florida and various other similar environments around the world, where it lives usually upside-down on the bottom. Where found, there may be numerous individuals with varying shades of white, blue, green and brown. They have a mild sting since they are primarily photosynthetic, but sensitive individuals may have a stronger reaction. The stinging cells are excreted in a mucus; swimming over these jellies (especially using swim fins) may cause transparent, essentially invisible, sheets of this mucus to be lifted up into the water column, where they are then encountered by unsuspecting swimmers. The stings, appearing in the form of a red rash-like skin irritation, are notorious for being extraordinarily itchy.[Update: Dr Dawson says some Cassiopea have a very 'sharp' sting, so be careful!]
The Cassiopea jellyfish is also called "Upside Down Jellyfish", because it lies on its back, so that the bell touches the ground. In this position it resembles a sea anemone. Sometimes this jellyfish is picked up by a crab (Dorippe frascone) and carried on its back. The crab uses the jellyfish to defend itself against possible predators.
Some times of the year, really gigantic jellyfishes are seen washed ashore on Changi.
This is one of two enormous jellyfishes we saw washed up on the shores of Changi. They were about 50cm in diameter. Dr Dawson says this one belongs to Order Rhizostomeae, but there isn't enough details in the photo to be sure which kind it is.
This jellyfish stranded on the Changi shore was about 40cm in diameter! That's Chay Hoon's foot in the top left corner of the photo. Dr Dawson says from the patterning on the bell, it may be Versuriga sp., Class Scyphozoa, but requires a closer look to be sure.
This may be Aequorea sp., Class Hydrozoa. From the Aequorea entry on wikipedia: Some common names of this animal include Crystal jelly. Aequorea victoria found off the west coast of North America is reported to be bioluminescent. The Singapore one in this photo was seen in the daytime, so we didn't see any bioluminescence.
This could be either Rhopilema sp., Class Scyphozoa or Acromitus sp., Class Scyphozoa (small details under the bell-shaped part of the animal needs to be examined to be sure). This is a small jellyfish, which I though looked very much like the next one. This shows that it's important to document all animals even if they look similar.
This is Acromitus, Class Scyphozoa. Sometimes, the waters at Chek Jawa are teeming with these small chubby jellyfishes which move in short bobs as they energetically contact their small bell-shaped bodies.
More jellyfish photos in this wildsingapore flickr set.
Have a look at Dr Michael N Dawson's fabulous Dawson Lab website with lots of photos of cool marine life from all over the world; as well as his awesome The Scyphozoan website with lots of info about jellyfishes in Class Scyphozoa.
Dr Dawson subsequently shared some detailed tips on how to photograph jellyfishes for identification.
