Squirts

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 within the invertebrates (animal lacking a backbone), however in their larval stage they do possess primitive vertebrate characteristics.

Sea squirts are common on local beaches. They are sessile animals, with the best places to find them is under rocks and fixed to large brown seaweeds.

Depending on the species, sea squirts live solitary or together in colonies. Solitary forms are stand alone individuals, while those in colonies may share “body parts”.

With solitary sea squirts the body has a tunic, a sturdy outer skin which supports the animal. There are two siphon openings which allow a flow of water through the body. Water is drawn through the inhalant siphon, the water flow being sustained by the beating of cilia and then expelled via the exhalent siphon. As the water circulates through the body; food and oxygen are removed from it; and waste products and gametes are expelled. The expelling of water can be in a squirt, (hence the name) this often happens when a squirt is handled.

In colonial forms individual squirts share a tunic. Each squirt has their own inhalant siphon to draw in the water, but may share an exhalant siphon.

Colonial Sea Squirts

Reproduction strategies vary depending on the species, including budding and more interestingly via a free swimming tadpole like larvae. This tadpole is only one stage in the reproduction cycle of many sea squirts. It is an important stage scientifically, as these free swimming larvae have a notochord and a dorsal nerve chord. These are traits of a backbone allowing sea squirts to be classified as chordata. However after the larvae metamorphose the traits are lost and are not found in the adult.

Sea Squirts Found on Cornish Shores

     Star Ascidian Botryllus schlosseri

  Ciona intestinalis

     Botrylloides leachi

  Dendrodoa grossularia

Star Ascidian Botryllus schlosseri  

These sea squirts share a background jelly the colour of which (green in this case) can vary. Individual animals align themselves in star shapes.

Each arm of the star is an individual. Individuals have their own inhalant siphon, but all in the star share an exhalant opening in the star's centre.

As for all of the squirts, star ascidians are sessile animals. They can be found encrusting rocks and seaweeds.

The specimen here was found on fronds of a large brown seaweed, thrown up on shore after a storm.

Botrylloides leachi

A colonial sea squirt which is often confused with the Star Ascidian and like it, is found encrusting rocks and attached to large brown seaweeds. The colour greatly varies. It can be distinguished from the Star Ascidian which has a star like arrangement while with Botrylloides leachi the individuals tend to be in parallel chains.

Ciona intestinalis

A large solitary sea squirt that can reach over 6 inches. Both siphons are distinct. If handled it readily squirts.

Dendrodoa grossularia

A solitary sea squirt found in small groups under rocks. They are red and rounded about the size of a marble. They have two small projections the siphons.