Coral can also be classified to fall into these structural categories: massive, columnar, encrusting, branching, foliceaous, laminar and free-living coral. The hard corals found in Mu Ko Similian National Park are deep water species of mostly staghorn coral types (Acropora echinata) and the smaller cauliflower shaped types (Seriatopora histrix). Many other species of marine life co-exist within the coral reef: Gorgonian sea fans, flower-like soft coral, several species of crabs, spiny painted lobsters, squid, sponges, sea cucumbers and giant clams.
Above the sea surrounding each island lies Beach forest, which steadily becomes Tropical forest further inland. Important tree species include Manilkara sp. Cordia subcordia, and Tournefotia argentia. A survey conducted in 1992 revealed that 39 species of birds can be found on the nine islands. Resident species include the Brahminy Kite, and the White-breasted Waterhen, while migratory species include the Pintail Snipe, and Grey Wagtail. Temporary migratory species include the Barn Swallow, Cattle Egret, Watercock, and the Roseate Tern. The most commonly seen species include the Pacific Reef-Egret, Nicobar Pigeon, Pied Imperial Pigeon, White-bellied Sea-Eagle, and the Collared Kingfisher.
The environment of Mu Ko Similian National Park is obviously that of a small island, wherever you go, you are not far from the sea. Natural fresh water reserves are few, and as a result, large mammal species cannot exist. Surveys have revealed that 27 species of small mammals exist within the park, including 16 species of bats namely: the black-bearded tomb bat, the lesser false vampire bat, the intermediate horseshoe bat, the lesser bent-winged bat, and the hairless bat. 3 species of squirrels can be found including the gray-cheeked flying squirrel. 4 species of rats: the yellow Rajah rat, the ricefield rat, roof rat and noisy rat can be seen scurrying around as well. Finally, the more unusal but fairly common residents include the bush tailed porcupine, common palm civet, flying lemur and the bottlenosed dolphin. 22 species of reptiles and amphibians can be found in the park including the banded krait, reticulated python, white-lipped pit viper, common pit viper, garden blue lizard, hawksbill turtle, leather turtle, bengal monitor lizard, common water monitor lizard, ornate froglet, common asiatic frog, marsh frog, and the common bush frog. Finally, another most interesting species located in the Similans island is called the hairy leg mountain land crab. This crab is found in such large numbers you will be sure to see many just by walking around a bit. No matter where you are on the island, seeing this creature will be a reminder you are never far from water.