Sea squirts (Tunicata)

The species group can often be identified without enlarging aids
  • Vase tunicate (Ciona intestinalis) on a Virtue disc. Photo: Mikael Olsson
  • Light-bulb sea squirt (Clavellina lapadiformis)
  • Star ascidian (Botryllus schlosseri) on a Virtue disc. Photo: Mikael Olsson

Sea squirts (Ascidiacea) belongs to the tunicates (Tunicata). They are sessile animals and growing individually (solitary) or forming colonies. They often grow in large numbers alongside each other. The body resembles a sack and has a large pharynx and a protective cover, called the mantle. The appearance and colour of sea squirts varies greatly. Large or very small, colorful or transparent. Appearance and colour can also vary within a species. One of the most common sea squirts is the Vase tunicate (Ciona intestinalis) - here on a Virtue disc. Sea squirts are "eating", as they take in water through an intake opening, called a siphon. The water is then filtered through the pharynx and flows out through the outflow opening. Small nutrient particles stick that way and are transported to the stomach. Sea squirts are filter feeders. Sea squirts are usually hermaphroditic but many can also reproduce asexually. As larvae they are small and free swimming. In Swedish waters there are about 20 species and many are common on the Swedish west coast. Across the world, there are more than 2000 species described.


More information in Aquascope:

About the Vase tunicate

Gas Mantle Ascidian

About the Light-bulb sea squirt

Baked bean ascidian