Ciona intestinalis
[7][8] Although Linnaeus first categorised this species as a kind of mollusk, Alexander Kovalevsky found a tadpole-like larval stage during development that shows similarity to vertebrates.Ciona intestinalis is a solitary tunicate with a cylindrical, soft, gelatinous body, up to 20 centimetres (8 in) long.The body is attached by a permanent base located at the posterior end, while the opposite extremity has two openings, the buccal and atrial siphons.The potential impact of C. intestinalis and its introduction to new habitats can be avoided, so most agencies suggest that fish and shellfish harvesters are to avoid transfer of harvested shellfish and fishing gear to other areas, and to dry gear thoroughly before transfer, along with inspecting boat hulls.[13] Self/non-self-recognition molecules are considered to play a key role in the process of interaction between sperm and the vitelline coat of the egg.[13] Self-incompatibility promotes out-crossing which provides the adaptive advantage at each generation of masking deleterious recessive mutations (i.e. genetic complementation).