Asteroidea or starfishes (sea stars)
Starfishes are easily identified among shallow water invertebrates . The skeletal plates in most species are well developed and give the starfishes a relatively solid shape, sometimes with a geometric pattern that underlines the skeletal plates.. The number of arms is typically 5 (to follow the pentameric symmetry characteristic of the echinoderms) but exceptions are numerous both within a given species where specimens with different numbers of arms are common and between species where some species have 6, 7 or sometimes a large number of arms.
Most starfishes are carnivore and feed on small invertebrates (often mollusks). They expel their stomach (like returning a sock) through the mouth to digest their prey externally. Like sea urchin, the upper part of the body is called the aboral surface whereas the surface in contact with the substrate is the oral (where the mouth is located) surface.
There are some 20 known species of Asteroids in the shallow waters of Oman. Some of them appears restricted to the Arabian Sea and others occurring in both the Sea of Oman and the Arabian Sea.
In this guide, we are not following the typical Class, Order, Family… classification as many of the characters needed cannot easily be observed on the animals underwater. Instead we are going to follow a “shape” and “color” approach.
Sea stars without distinct arms or or with arms shorter than the diameter of the central disk
Starfish with long arms, 2-3 times the diameter of the disk
Starfish with long tapering arms, often 4-10 times the diameter of the disk
