The tropical coral reefs are the most beautiful ecosystem in the world.
There, I said it.
These are Jellyfish that have eight divided arms hanging from the bell, rather than tentacles.
Cassiopeia ornata, 'Upside-down Jellyfish'.
The flatworms on coral reefs can be confused with the nudibranch sea slugs, however the latter have obvious fluffy appendages (the Spanish Dancer is an example).
Thysanozoon flavomaculatum, 'Yellow spot Flatworm', 'Gold-flecked Flatworm'.
This group includes the 'true' worms of the soil and sea.
Like the 'Feather Duster Worms' of the Family Sabellidae, these worms also have two fans extending from the tube, however they differ in that the tube is hard and made from calcium carbonate. When disturbed they withdraw quickly and seal their tube off with the operculum.
Protula bispiralis, 'Magnificent Tube Worm'. Two relatively large spires, with several beautifully delicate whorls. Orange and cream in colour. Tube often extending obviously from reef.
Spirobranchus, 'Christmas Tree Worms'. Small and very common 'fluffy' feeding tentacles that usually grow out of the top of Boulder Coral in groups, and appear in many different colours. The tentacles suck back in quickly when the snorkeller gets too close.
There are at least three species in this genus. Blue-ringed Octopuses infamous for being one of the most venomous animals in the world. It is thought that the toxins from one small individual animal could kill over 25 people in one dose. The list of chemicals in the venom include: 5-hydroxytripamine, hyaluronidase, tyramine, histamine, tryptamine, taurine, acetylcholine, dopamine and tetrodotoxin; it is the latter that is most dangerous. Tetrodotoxin is found in pufferfish, and is reported to be some 100 times more toxic than cyanide. When the victim is bitten, they are partly paralysed, including the diaphragm, and thus unable to breath, and can die within minutes if not treated. There is no antidote.
Hapalochlaena lunulata, 'Greater Blue-Ring Octopus'. Despite the common name, like all Blue-ring Octopuses, this animal is quite small, with short arms, and could fit in the palm of your hand - but don't pick it up! They are found around rubbly coral reefs across northern Australia, New Guinea and tropical Asian waters.
Featherstars usually attach to coral on the edge of drop-offs and/or near areas with some flow of water. They are capable of 'swimming' freely. There is a huge range of colours and combinations of colours.
Polycarpa aurata. 'Gilded/Oxheart/Goldmouth/Ink Spot/ Yellow & Purple Ascidian/Sea Squirt'. One of the most obvious and commonly seen sea squirts on coral reefs.
Didemnum molle, 'Green Sea Squirt'. A commonly seen sea squirt on coral reefs throughout the Indo-Pacific. It appears soft and squishy and swishes around in reaction to water movements. Another common sea squirt thay look similar is called Atriolum robustum. Or maybe I have these the wrong way around?
A salp chain.
Aetobatus narinari, 'Spotted Eagle Ray'.
There are half a dozen turtle species that can be seen around the tropical Indo-Pacific coral reefs. While they look superficially similar, if you can get a photograph or a good look, you should be able to identify them.
The first step is to look at the lateral scutes (large scales in a line along either side) of the back of the carapace (shell). If the carapace has no scales, and the carapace is ridged, then that's easy - it is a Leatherback! (although these turtles are more commonly seen out to sea rather than around coral reefs).
If the there are four lateral scutes, then it is either a Green Turtle, Hawksbill or a Flatback Turtle. Also, the first lateral scute does not touch the nuchal (the small thin scute on the very front leading edge of the carapace, just behind the head). If the carapace is slightly upturned along the edge, then it is Flatback. The next step is to look at the head. The Green Turtle (and the Flatback) both have one large prefrontal scale along the front of the eye, while the Hawksbill clearly has two (as well as a more parrot-like beak).
If there are five or more scutes along the outer edge of the carapace, then it is either a Loggerhead or an Olive Ridley. Also, the first lateral scute does touch the nuchal. The Loggerhead has either five or six lateral scutes, the shell itself is elongated in shape, and the turtle has a large head. The Olive Ridley has a more rounded shell with six or more thin lateral scutes.
Chelonia mydas, 'Green Turtle'. The most widespread and commonly seen of the marine turtles.
Eretmochelys imbricata, 'Hawksbill Turtle'. Similar looking to Green Turtle, but with longer head and distinct 'parrot beak'. Note the two prefrontal scutes in front of the eye (split by a lighter edge) and the first lateral scute of the shell not touching the nuchal.
Esacus magnirostris, 'Beach Thick-knee/Stone-Curlew'.
Egretta sacra, 'Eastern Reef Egret' grey morph.
Egretta sacra, 'Eastern Reef Egret' white morph.
Pandion cristatus, 'Eastern Osprey'.
Haliaeetus leucogaster, 'White-bellied Sea-Eagle'.
The biggest reef in the world is of course the Great Barrier Reef, off eastern Australia. Along the edge of this reef are the beautiful Ribbon Reefs. There is also Lizard Island, On the west coast of Australia there are other reefs, including Montgomery Reef in the north east, and further south is Ningaloo Reef.
The south west Pacific includes the Solomon Islands, my favourite country for snorkelling. One of the best sites in this area is at Maravagi Resort, on Mangalonga Island. Other areas in the Solomon Islands include: Uepi Resort, Marovo Lagoon and Arnavon (Arnarvon) Islands.
At a similar latitude is the relatively unspoilt island of New Guinea. This includes the most diverse coral reefs in the world, at Rajah Ampat.
Heading north there are the remote islands of Micronesia, including Palau. Then there is the diverse and many islands of the Philippines, including Panagsama. Even further north is the extent of tropical coral reefs, Japan. Here, snorkelling is easy at Miyako Island.