Yellow Sea Squirt

Appearance

The size and shape of solitary ascidians are highly variable and may look like seed, potato, grape or peach. The shape of the yellow sea squirt can vary from being long andclub-shaped to curved, however most are laterally flattened. While some individuals have been recorded to be as big as 15cm, most are about 5cm long.

The yellow sea squirt has two indented siphons used to intake and reject water. One oral (also called branchial) siphon located on the posterior end of the ascidian, through which water enters the body, and one atrial siphon located along the dorsal side of the body, through which the waters evacuates the body.

Behavior

Like most other solitary ascidian, the yellow sea squirts are suspension feeders.

They feed by absorbing water through their oral siphon with the help of cilia which are tiny hair-like appendages found on the edge of the gill slit. Cilia create a current which pump water into the pharynx through a mucus net, trapping the suspended particles. This mucus net is produced by the endostyle and located inside the branchial basket of the ascidian. The water will then exit the ascidian via the atrial siphon.
Similarly, the water is also taken to the gill slits where respiration takes place.

Phallusia julinea is a species of solitary hermaphrodite as all ascidians. Solitary ascidians are oviparous having both an egg sac and sperm duct. Fertilization occur in seawater where the eggs and sperm are released through the atrial siphon.

Ascidian larvae are free-swimming, they move with their post-anal tail, just like any other chordates. The larval phase, which can last from minutes to hours, correspond to the time needed for the larvae to reach competency and find a suitable habitat to settle and go through metamorphosis. Once settled, the ascidian becomes a sessile organism and does not move for the rest of its life.