arm

noun

In asteroids and ophiuroids, the ray, a lateral extension of the main body or central disk, typically 5 or multiples of 5. Contains extensions of the water vascular system, ossicles, nerves, the hemal system, and in some contains branches of the reproductive system and gut.
Geography: a long and narrow body of water branching from a lake or an inlet of the sea or formed from flooding of an inlet streambed.