Facts about sea squirts

The filter feeding animal Ciona intestinalis is a species in the animal group ascidia. The English common name is Sea vase tunicate. The larvae of the ascidia have all characters that vertebrates (animals with vertebras) have, for example a presence of a notochord (a simpler kind of spinal cord). The notochord regresses when the larva develops into an adult animal. In other words: A simple spinal cord is present when the larvae makes active choices about where to settle due to a need to process stimuli for finding a good spot – but after settling it does not need to \"think\" any more, it only filters the water and reproduces. As such it is an invertebrate animal.

Ciona intestinalis is a generalist in terms of requirements on temperature and salinity. It occurs naturally from just below the surface down to several hundred meters of depth. In Swedish waters the Ciona reproduces twice a year in the surface layer (0-20 m) but only once per year in deeper and colder water.

The life cycle of Ciona is characterized by rapid growth (~20 mm/month), early sexual maturity at 8-10 weeks and a high reproduction (> 10 000 eggs per individual). The eggs are released either individual or in mucous strings, the latter is assumed to prevent long-range transport and encourage the formation of local colonies when the location is favourable.

Ciona is a hermaphroditic animal but avoid self-fertilisation by partially produce eggs and sperm at different times, meaning that eggs and sperm from an individual will not be able to fertilize each other. The eggs are fertilized in the water outside of the animal and the larva is quickly developed.

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