Sea Squirts also known as ascidians, are a marine class of animals that fall between the invertebrates and the vertebrates. They are simple animals that are often categorised with the invertebrates, however in their larval stage they do possess primitive vertebrate characteristics.
Although, as here, they may form clusters these particular sea squirts live as individual animals. They feed by siphoning nutrients from sea water. There are two short tubes or siphon openings which allow a flow of water through the body. Water is drawn through the inhalant siphon, and then expelled via the exhalent siphon. As the water circulates through the body; food and oxygen are removed from it and waste products are expelled.
If they are disturbed, they will force the water they contain out of both siphons at the same time which is how they get their name of sea squirt.
Brittle stars or ophiuroids are echinoderms in the class Ophiuroidea closely related to starfish. They differ from starfish in that they have an obvious circular central disc from which arise the five thin, very flexible arms which break easily, hence the name. They often occur in large number under stones lying on gravel and rough sand between large rocks.They crawl across the sea floor using their flexible arms for locomotion. Because the ophiuroids have longer, more slender arms than starfish, they are also known as serpent stars; the class name Ophiuroidea is derived from the Greek meaning "serpent".