''Ciona savignyi'' is a marine animal sometimes known as the Pacific transparent sea squirt or solitary sea squirt. It is a species of

tunicate Tunicates are marine invertebrates belonging to the subphylum Tunicata ( ). This grouping is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords (including vertebrates). The subphylum was at one time ...

s in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Cionidae. It is found in shallow waters around Japan and has spread to the west coast of North America where it is regarded as an invasive species.

Description

''Ciona savignyi'' is a solitary, bottle or vase-shaped tunicate growing to a length of about . It is usually broader near the base and this part is permanently attached to a hard surface. The outer covering or tunic is soft and gelatinous, translucent, whitish or cream-coloured. The muscle bands and internal organs can often be seen through the tunic. At the narrower, free end, there is a buccal siphon through which water is drawn into the animal. This opening is rimmed by eight yellow-edged lobes each with an orange-red spot. At the side, not far from the buccal siphon, there is an atrial siphon out of which water is pumped. This has six similar yellow lobes with red spots. Five to seven muscle bands run longitudinally along the tunic and the siphons can be retracted when danger threatens. This species can be mistaken for the very similar ''

Ciona intestinalis ''Ciona intestinalis'' (sometimes known by the common name of vase tunicate) is an ascidian (sea squirt), a tunicate with very soft tunic. Its Latin name literally means "pillar of intestines", referring to the fact that its body is a soft, tran ...

'' but ''Ciona savignyi'' has white flecks in the tunic wall which ''C. intestinalis'' lacks. Nor does ''C. intestinalis'' have any reddish colour associated with its buccal siphon.

Distribution

''Ciona savignyi'' is native to Japan, and possibly also to

Alaska Alaska ( ) is a non-contiguous U.S. state on the northwest extremity of North America. Part of the Western United States region, it is one of the two non-contiguous U.S. states, alongside Hawaii. Alaska is also considered to be the north ...

and

British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...

. In 1985 it was recorded at

Long Beach Harbor The Port of Long Beach, administered as the Harbor Department of the City of Long Beach, is a container port in the United States, which adjoins Port of Los Angeles. Acting as a major gateway for US–Asian trade, the port occupies of land w ...

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

and since then it has spread to a number of other locations in the state. By 1998 it had also been reported in

Puget Sound Puget Sound ( ; ) is a complex estuary, estuarine system of interconnected Marine habitat, marine waterways and basins located on the northwest coast of the U.S. state of Washington (state), Washington. As a part of the Salish Sea, the sound ...

and the

San Juan Islands The San Juan Islands is an archipelago in the Pacific Northwest of the United States between the U.S. state of Washington and Vancouver Island, British Columbia, Canada. The San Juan Islands are part of Washington state, and form the core of ...

. It favours

docks The word dock () in American English refers to one or a group of human-made structures that are involved in the handling of boats or ships (usually on or near a shore). In British English, the term is not used the same way as in American Engli ...

piling A pile or piling is a vertical structural element of a deep foundation, driven or drilled deep into the ground at the building site. A deep foundation is a type of foundation that transfers building loads to the earth farther down from th ...

marina A marina (from Spanish , Portuguese and Italian : "related to the sea") is a dock or basin with moorings and supplies for yachts and small boats. A marina differs from a port in that a marina does not handle large passenger ships or cargo ...

harbour A harbor (American English), or harbour (Commonwealth English; see American and British English spelling differences#-our, -or, spelling differences), is a sheltered body of water where ships, boats, and barges can be Mooring, moored. The t ...

s and

aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. Nelu ...

structures and is thought to have spread in

ballast Ballast is dense material used as a weight to provide stability to a vehicle or structure. Ballast, other than cargo, may be placed in a vehicle, often a ship or the gondola of a balloon or airship, to provide stability. A compartment within ...

water or via the hulls of ships. It is regarded as an

invasive species An invasive species is an introduced species that harms its new environment. Invasive species adversely affect habitats and bioregions, causing ecological, environmental, and/or economic damage. The term can also be used for native spec ...

in the United States. The first record of the species in the southern hemisphere came from

Nelson, New Zealand Nelson () is a List of cities in New Zealand, city and Districts of New Zealand, unitary authority on the eastern shores of Tasman Bay at the top of the South Island of New Zealand. It is the oldest city in the South Island and the second-old ...

in April 2010. Since then it has been found in port and harbor areas in

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

, and in

Hobart Hobart ( ) is the capital and most populous city of the island state of Tasmania, Australia. Located in Tasmania's south-east on the estuary of the River Derwent, it is the southernmost capital city in Australia. Despite containing nearly hal ...

, Australia in 2017. While its environmental impact is unclear, the species is able to form dense patches which inevitably compete with native species for planktonic food.

Biology

''Ciona savignyi'' is a filter feeder. The water drawn in through the buccal siphon passes through a mucus net where

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

ic particles are caught. Periodically, this is rolled up and swallowed and a new net is secreted. The water is expelled through the atrial siphon. Like other tunicates, ''Ciona savignyi'' is a

hermaphrodite A hermaphrodite () is a sexually reproducing organism that produces both male and female gametes. Animal species in which individuals are either male or female are gonochoric, which is the opposite of hermaphroditic. The individuals of many ...

. The male and female gonads do not ripen simultaneously so it does not normally self-fertilise. Gametes are released into the sea and after fertilisation, the eggs hatch into

tadpole A tadpole or polliwog (also spelled pollywog) is the Larva, larval stage in the biological life cycle of an amphibian. Most tadpoles are fully Aquatic animal, aquatic, though some species of amphibians have tadpoles that are terrestrial animal, ...

-like

larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

e. After a few days of development these attach themselves to a firm surface and undergo

metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth transformation or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and different ...

into juvenile tunicates. ''Ciona savignyi'' has one of the highest known levels of genetic diversity of any species. ''Ciona savignyi'' is highly self-fertile. However, non-self sperm outcompete self-sperm in fertilization competition assays. Gamete recognition is not absolute allowing some self-fertilization. It was speculated that self-incompatibility evolved to avoid

inbreeding depression Inbreeding depression is the reduced biological fitness caused by loss of genetic diversity as a consequence of inbreeding, the breeding of individuals closely related genetically. This loss of genetic diversity results from small population siz ...

, but that selfing ability was retained to allow reproduction at low population density.

References

{{Authority control Phlebobranchia Animals described in 1882 Taxa named by William Abbott Herdman