The branching corals Pocillopora and Acropora often harbour many animals, in particular crustaceans. Most do not harm their host, and one crab, Trapezia has been shown to protect the coral against the coral-eating Crown-of-Thorns starfish (Acanthaster planci).
These are coral obligates. Trapezia (left), is usually found on Pocillopora (shell width up to 1.5cm), mainly feeding on the mucus secreted by the corals and in return, protect the coral from would-be predators.
Resembling and behaving similarly but with a narrower "waist" and a cream coloured body is Tetralia (right) (width up to lcm) which prefers the Stag Horn Coral Acropora.
Green Coral Shrimp
This shrimp (length 1-2cm) is an obligate on Pocillopora. Their two pincers have been modified such that they can produce a successive series of clicks when disturbed, like snapping shrimps.
This goby lives between the branches of corals, its colour being a striking green with various hues. The fused base of the ventral fins is still present in this fish. Each coral head normally houses a pair of these gobies, the male being much smaller. (Length up to 3cm).
From A Guide to Seashore Life by Dr Leo W H Tan and Peter K L Ng
Published by the Singapore Science Centre and sponsored by BP
@Raffles Museum of Biodiversity Research and Singapore Science Centre