My preliminary identification for 

Picture 1 - Acanthaster placi

Picture 2 - Nardoa frianti

Picture 6 - Synapta maculata

Please help validate. Thanks

5 looks like Protoreaster nodosus

1 is definitely acanthaster (Crown of thorns) 

Nicholas, yes, it seems like a P. nodosus. A juvenile, you think?

Honestly I am not sure. I only know of this species form the aquarium hobby. They can grow larger than 10 cm across, but as far as life stage, I'm not quite sure. 

Picture 7 is a sea urchin most likely belonging to Family Toxopneustidae and Genus Tripneustes. Based on you picture identification of species will be difficult, perhaps T. gratilla

Picture 5 is most likely Protoreaster nodosus

Picture 4 is most likely juvenile Protoreaster nodosus

Picture 1 is definitely Acathaster planci

The other 3 I am not sure about

Tom

Tomas - you think both picture 4 and 5 are species of P. nodosus? Thanks! 

Angelo,

I think so. The 4th picture is a very small specimen and I have seen similar specimens in Indonesia. However, making a definitive identification from a picture is not the best way. Best way to do it is t get a key. I hope you can get one.

Tom

Thanks! I really appreciate it.

Angelo,

Clark and Row 1971 is a good key to start with. I am attaching an old PDF I have but in case it is too big of a file you can trace it here as well:

http://www.abctaxa.be/downloads/additional-information-volume-1/works-famous-holothuroid-workers/fwe-rowe/MonographIndoWestPacific.pdf

Another good key is by VandenSpiegel et al 1998. The Asteroid fauna (Echinodermata) of Singapore, with a distribution table and the illustrated identification to the species The Raffles Bulleting of Zoology 46(2) 431-470

Hope this helps, Tom

Thank you very much, Tom! i really appreciate it.

How about this, Tom? Is this still T. gratilla?

It looks that way. Looking at the clean tests should confirm it. Where did you find it? Habitat can also offer some clues which species it is. When you found it was it covered by benthic detritus or debris of some sort? T. gratilla is known to cover itself with small debris for camouflage.

Cheers, Tom