Tunicates, also known as
urochordates, are members of the
subphylumIn life, a subphylum is a taxonomic rank intermediate between phylum and superclass. The rank of subdivision in plants and fungi is equivalent to subphylum.Not all phyla are divided into subphyla...
Tunicata or
Urochordata, a group of underwater saclike
filter feederFilter feeders are animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feeding are clams, krill, sponges, some fish and sharks, and baleen whales. Some birds, such...
s with incurrent and excurrent
siphonsThe term siphon is used for a number of biological structures, either because flowing liquids are involved, or because the object is shaped like a siphon...
that is classified within the phylum Chordata. While most tunicates live on the ocean floor and are commonly known as
sea squirts and
sea pork, others – such as
salpA salp is a barrel-shaped, free-floating tunicate. It moves by contracting, thus pumping water through its gelatinous body...
s,
doliolidsDoliolida are small marine animals of the Tunicata phylum, related to salps and pyrosomas. Doliolid body is small, typically 1-2 cm long, and barrel-shaped; it features two wide siphons, one at the front and the other at the back end, and eight or nine circular muscle strands reminiscent of barrel...
and pyrosomes – live above in the
pelagic zoneAny water in the sea that is not close to the bottom is in the pelagic zone. The word pelagic comes from the Greek πέλαγος or pélagos, which means open sea....
as adults.
Most tunicates feed by filtering sea water through pharyngeal slits, but some are sub-marine
predatorsIn ecology, predation describes a biological interaction where a predator feeds on its prey, . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of the prey...
such as the
Megalodicopia hians. Like other
chordateChordates are animals which are either vertebrates or one of several closely related invertebrates. They are united by having, for at least some period of their life cycle, a notochord, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail...
s, tunicates have a
notochordThe notochord is a flexible, rod-shaped body found in embryos of all chordates. It is composed of cells derived from the mesoderm and defines the primitive axis of the embryo. In some chordates, it persists throughout life as the main axial support of the body, while in most vertebrates it is...
during their early development, but lack myomeric segmentation throughout the body and
tailThe tail is the section at the rear end of an animal's body; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammals and birds...
as adults. Tunicates lack the kidney-like
metanephridialNephridia are invertebrate organs which function similar to kidneys. They remove metabolic wastes from an animal's body. They are present in many different invertebrate lines. There are two basic types, metanephridia and protonephridia, but there are other types.-Metanephridia:A metanephridium...
organs, and the original
coelomThe coelom is a fluid filled cavity formed within the mesoderm. Coeloms developed in triploblasts but were subsequently lost in several lineages. Loss of coelom is correlated with reduction in body size...
body-cavity develops into a
pericardial cavityThe pericardial cavity is a potential space between the parietal pericardium and visceral layer. It contains a supply of serous fluid. The serous fluid that is found in this space is known as the pericardial fluid....
and gonads. Except for the
pharynxThe pharynx is the part of the neck and throat situated immediately posterior to the mouth and nasal cavity, and cranial, or superior, to the esophagus, larynx, and trachea.-Functions:...
,
heartThe heart is a muscular organ found in all vertebrates that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
and gonads, the organs are enclosed in a membrane called an
epicardiumEpicardium describes the outer layer of heart tissue . When considered as a part of the pericardium, it is the inner layer, or visceral pericardium....
, which is surrounded by the jelly-like
mesenchymeMesenchyme, or mesenchymal connective tissue, is an example of reticular connective tissue, a type of loose connective tissue, which is derived from all three germ layers and located within the embryo . Mesenchyme is characterized morphologically by a prominent ground substance matrix containing a...
. Tunicates begin life in a mobile
larvaA larva is a young form of animal with indirect development, going through or undergoing metamorphosis ....
l stage that resembles a
tadpoleA tadpole, polliwog , or pollywiggle is the wholly aquatic larval stage in the life cycle of an amphibian, particularly of a frog or toad.- Appellation :The name "tadpole" is from Middle English taddepol, made up of the elements tadde, "toad", and...
, later developing into a barrel-like and usually sedentary adult form.
Tunicates apparently evolved in the early Cambrian period, beginning
c 540 million years ago. Despite their simple appearance, tunicates are closely related to vertebrates, which include fish and all land animals with bones.
Life cycle
Most tunicates are
hermaphroditeIn a biological context, a hermaphrodite is an animal or plant that has both male and female reproductive organs.Many taxonomic groups of animals , do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which both partners can...
s. The eggs are kept inside their body until they hatch, while sperm is released into the water where it fertilizes other individuals when brought in with incoming water.
Some larval forms appear very much like primitive
chordateChordates are animals which are either vertebrates or one of several closely related invertebrates. They are united by having, for at least some period of their life cycle, a notochord, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail...
s with a
notochordThe notochord is a flexible, rod-shaped body found in embryos of all chordates. It is composed of cells derived from the mesoderm and defines the primitive axis of the embryo. In some chordates, it persists throughout life as the main axial support of the body, while in most vertebrates it is...
(stiffening rod). Superficially the
larvaA larva is a young form of animal with indirect development, going through or undergoing metamorphosis ....
resemble small
tadpoleA tadpole, polliwog , or pollywiggle is the wholly aquatic larval stage in the life cycle of an amphibian, particularly of a frog or toad.- Appellation :The name "tadpole" is from Middle English taddepol, made up of the elements tadde, "toad", and...
s. Some forms have a calcereous
spiculeSpicules are tiny spike-like structures of diverse origin and function found in many organisms, such as the copulatory spicules of certain nematodes or the grains on the skin of some frogs....
that may be preserved as a
fossilFossils are the preserved remains or traces of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous rock formations and sedimentary layers is known as the fossil record...
. They have appeared from the
JurassicThe Jurassic is a geologic period and system that extends from about Ma to Ma, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the "Age of Reptiles". The start of the period is marked by...
to the present, with one proposed
NeoproterozoicThe Neoproterozoic Era is the unit of geologic time from 1,000 to 542.0 ± 1.0 million years ago. The terminal Era of the formal Proterozoic Eon , it is further subdivided into the Tonian, Cryogenian, and Ediacaran Periods...
form,
YarnemiaYarnemia is a fossil dubiously classified in the urochordata family. While urochordates and yarnemia look similar, the oldest commonly-accepted urochordate dates to the Jurassic period, while yarnemia is Ediacaran....
.
The larval stage ends when the tunicate finds a suitable rock to affix to and cements itself in place. The larval form is not capable of feeding, and is only a dispersal mechanism. Many physical changes occur to the tunicate's body, one of the most interesting being the digestion of the cerebral ganglion, which controls movement and is the equivalent of the human brain in some arthropods and insects. From this comes the common saying that the sea squirt "eats its own brain". In some classes, the adults remain pelagic (swimming or drifting in the open sea), although their larvae undergo similar metamorphoses to a higher or lower degree.
Once grown, adults can develop a thick covering, called a
tunic, to protect their barrel-shaped bodies from enemies.
During embryonic development, tunicates exhibit "determinate cleavage", where the fate of the cells is set early on with reduced cell numbers and
genomeIn modern molecular biology the genome refers to all of its hereditary information encoded in DNA .The genome includes both the genes and the non-coding sequences of the DNA. The term was adapted in 1920 by Hans Winkler, Professor of Botany at the University of Hamburg, Germany...
s that are rapidly evolving. In contrast, the amphioxus and vertebrates show cell determination relatively late in development and cell cleavage is indeterminate. The genome evolution of amphioxus and vertebrates is also relatively slow.
Feeding
Tunicates are suspension feeders. They have two openings in their body cavity: an in-current and an ex-current siphon. The in-current siphon is used to intake food and water, and the ex-current siphon expels waste and water. The tunicate's primary food source is
planktonPlankton consist of any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. Plankton are defined by their ecological niche rather than their phylogenetic or taxonomic classification...
. Plankton gets entangled in the
mucusIn vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. It is a viscous colloid containing antiseptic enzymes and immunoglobulins that serves to protect epithelial cells in the respiratory,...
secreted from the
endostyleAn endostyle is a longitudinal ciliated groove on the ventral wall of the pharynx which produces mucus to gather food particles. It is found in urochordates and cephalochordates, and in the larvae of lampreys. It aids in transporting food to the esophagus. It is also called the hypopharyngeal groove...
. The tunicate's
pharynxThe pharynx is the part of the neck and throat situated immediately posterior to the mouth and nasal cavity, and cranial, or superior, to the esophagus, larynx, and trachea.-Functions:...
is covered by miniature hairs called ciliated cells which allow the consumed plankton to pass down through to the
esophagusThe esophagus or oesophagus , sometimes known as the gullet, is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. The word esophagus is derived from the Latin œsophagus, which derives from the Greek word oisophagos , lit...
. Their guts are U-shaped, and their anuses empty directly to the outside environment. Tunicates are also the only animals able to create
celluloseCellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....
.
Tunicate
bloodBlood is a specialized bodily fluid that delivers necessary substances to the body's cells — such as nutrients and oxygen — and transports waste products away from those same cells....
is particularly interesting. It contains high concentrations of the transition metal
vanadiumVanadium is the chemical element with the symbol V and atomic number 23. It is a soft, silvery grey, ductile transition metal. The formation of an oxide layer stabilizes the metal against oxidation. Andrés Manuel del Río discovered vanadium in 1801 by analyzing the mineral vanadinite, and named it...
and
vanadium-associated proteinsVanabins are a specific group of vanadium-binding metalloproteins. Found only in the blood of some ascidians and tunicates , these organisms are able to concentrate vanadium to a level more than 100 times higher than in the surrounding seawater...
as well as higher than usual levels of
lithiumLithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number three. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...
. Some tunicates can concentrate vanadium up to a level one million times that of the surrounding seawater. Specialized cells can concentrate heavy metals, which are then deposited in the tunic.
Classification
Tunicates are more closely related to craniates (including
hagfishHagfish are marine craniates of the class Myxini, also known as Hyperotreti. Myxini is the only class in the clade Craniata that does not also belong to the subphylum Vertebrata...
,
lampreyA lamprey is a parasitic marine animal with a toothed, funnel-like sucking mouth. Translated directly, their name means stone lickers . While lampreys are well known for those species which bore into the flesh of other fish to suck their blood, these species make up the minority...
s, and jawed
vertebrateVertebrates are members of the subphylum Vertebrata, chordates with backbones or spinal columns. About 58,000 species of vertebrates have been described. Vertebrata is the largest subphylum of chordates, and contains many familiar groups of large land animals. Vertebrates comprise cyclostomes, bony...
s) than to
lanceletThe lancelets are the modern representatives of the subphylum Cephalochordata, usually said to be the sister group of the craniates. They are usually found buried in sand in shallow parts of temperate or tropical seas. In Asia, they are harvested commercially as food for humans and domesticated...
s,
echinodermEchinoderm, there are seven main classes of Echinoderms which are brittle stars, basket stars, sea urchins, sand dollars, sea lilies, feather stars, and sea cucumbers...
s, hemichordates,
XenoturbellaXenoturbella is a genus of bilaterian animals; it contains two marine worm-like species. The first known species was discovered in 1915 by Sixten Bock but the first published description was only in 1949 by Einar Westblad Its taxonomic position has been considered enigmatic since its discovery...
or other
invertebrateAn invertebrate is an animal without a vertebral column. The group includes 95% of all animal species — all animals except those in the Chordate subphylum Vertebrata ....
s . The
cladeA clade is a term used in modern alpha taxonomy, the scientific classification of living and fossil organisms, to describe a monophyletic group, defined as a group consisting of a single common ancestor and all its descendants.[The term "monophyletic group" is used in this article...]
comprising Tunicates and Vertebrates is called Olfactores.
The Tunicata contains about 3,000 species, usually divided into the following classes:
- Ascidiacea
Ascidiacea is a class in the Urochordata subphylum of sac-like marine invertebrate filter feeders. Ascidians are characterized by a tough outer "tunic" made of the polysaccharide tunicin, as compared to other tunicates which are less rigid.Ascidians are found all over the world, usually in shallow...
(Aplousobranchia, PhlebobranchiaPhlebobranchia is suborder of sea squirts in the order Enterogona. It describes a group of marine animals....
, and StolidobranchiaStolidobranchia is an order of tunicates in the class Ascidiacea. It describes a group of marine animals....
)
- Thaliacea
The Thalicea comprise a class of marine animals within the subphylum Urochordata. Unlike their bottom-dwelling relatives the ascidians, thaliaceans are free-floating for their entire lifespan. There are three orders of Thaliacea: Pyrosomida, Doliolida, and Salpida. Pyrosomes are colonies of tiny...
(Pyrosomida, DoliolidaDoliolida are small marine animals of the Tunicata phylum, related to salps and pyrosomas. Doliolid body is small, typically 1-2 cm long, and barrel-shaped; it features two wide siphons, one at the front and the other at the back end, and eight or nine circular muscle strands reminiscent of barrel...
, and SalpA salp is a barrel-shaped, free-floating tunicate. It moves by contracting, thus pumping water through its gelatinous body...
ida)
- Appendicularia (Larvacea
Larvaceans are solitary, free-swimming tunicates found throughout the world's oceans. Like most tunicates, appendicularians are filter feeders. Unlike other tunicates, appendicularians live in the pelagic zone, specifically in the upper sunlit portion of the ocean or sometimes deeper...
)
- Sorberacea
Sorberacea are benthic animals and a subgroup of the Tunicata . They superficially resemble sea squirts but prey on invertebrates such as crustaceans...
.
Although the traditional classification is followed for now, newer evidence suggests that the Ascidiacea is an artificial group. The new classification would be:
- Stolidobranchia,
- Phlebobranchia and Thaliacea,
- Aplousobranchia and Appendicularia,
- Sorberacea would belong somewhere in Ascidiacea, or be in a taxon on its own.
The species
Ciona intestinalisCiona intestinalis or vase tunicate is a Urochordata whose genome has been sequenced. It has become, over the past decade, a major experimental model for developmental biologists...
and Ciona savignyi have attracted interest in biology for developmental studies. Both species' genomes have been sequenced.
Sea squirts have become a testing ground in the controversy about the extent to which
cross-species gene transferHorizontal gene transfer , also Lateral gene transfer , is any process in which an organism incorporates genetic material from another organism without being the offspring of that organism. By contrast, vertical transfer occurs when an organism receives genetic material from its ancestor, e.g...
and hybridization have influenced animal evolution. In 1990,
Donald I. WilliamsonDonald Irving Williamson is a British planktologist and carcinologist, born 1922-01-08, Alnham, Northumberland, England. He gained his first degree from the Durham University in 1942, his Ph.D. from the same university in 1948, and a D.Sc. from the Newcastle University in 1972...
of the
University of LiverpoolThe University of Liverpool is a university in the city of Liverpool, England. It is a member of the Russell Group and the N8 Group for research collaboration, and founded in 1881 it is also one of the six original "red brick" civic universities...
(U.K.) fertilised sea squirt (
Ascidia mentula) eggs with
sea urchinSea urchins or urchins are small, spiny, globular animals that compose part of class Echinoidea. They are found in oceans all over the world. Their shell, or "test", is round and spiny, typically from 3 to 10 cm across. Common colors include black and dull shades of green, olive, brown, purple,...
(
Echinus esculentus) sperm resulting in fertile adults that resembled urchins, but Michael W. Hart of
Simon Fraser UniversitySimon Fraser University is a public university in British Columbia with its main campus on Burnaby Mountain in Burnaby, and satellite campuses in Vancouver and Surrey. It was established in 1965 and presently has more than 32,000 students and 900 faculty members. The university was named after...
failed to find sea-squirt DNA in tissue samples from the supposed hybrids. Williamson claims to have repeated the experiment with sea urchin eggs and sea squirt sperm, producing sea urchin larvae which developed into squirt-like juveniles. Michael Syvanen of the
University of CaliforniaThe University of California is a public university system in the state of California. Under the California Master Plan for Higher Education, the University of California is a part of the state's three-tier public higher education system, which also includes the California State University system...
has further suggested that sea squirts are themselves descended from a hybrid between a chordate and an ancestor of sea urchins. Like Williamson's, this idea has not yet gained support from embryologists and invertebrate zoologists.
Fossil record
Undisputed fossils of tunicates are rare. The best known (and earliest) is
Shankouclava shankouense from the Lower
CambrianThe Cambrian is the first geological period of the Paleozoic era, lasting from ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux...
Maotianshan Shale at Shankou village, Anning, near
KunmingKunming is a prefecture-level city and capital of Yunnan province, in southwestern China. Because of its year-round temperate climate, Kunming is often called the "Spring City" or "City of Eternal Spring" ....
(
South ChinaSouth China or Southern China can refer to:* An approximate region within China; see Northern and southern China* South Central China* Southwest China* South China , an ancient continent studied in geology-Other uses:...
).
There is also a common bioimmuration of a tunicate (
Catellocaula vallata) found in Upper
OrdovicianThe Ordovician is a geologic period and system, the second of six of the Paleozoic era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian period and is followed by the Silurian period...
bryozoanThe Bryozoa, also known as Ectoprocta, are a phylum of aquatic animals, typically about long, that sieve food particles out of the water using a retractable lophophore, a "crown" of tentacles lined with cilia. Most marine species live in tropical waters, but a few occur in oceanic trenches and...
skeletons of the upper midwestern United States.
There is also two enigmatic species from the
EdiacaranThe Ediacaran Period is the last geological period of the Neoproterozoic Era and of the Proterozoic Eon, immediately preceding the Cambrian Period, the first period of the Paleozoic Era and of the Phanerozoic Eon...
period -
Ausia fenestrataAusia fenestrata is a curious Ediacaran period fossil represented by only one specimen 5 cm long from the Nama Group of Namibia and it has similarity to new genus from Ediacaran siliciclastic sediments exposed on the Syuzma River of northern Russia.This fossil is of the form of an elongate...
from the Nama Group of
NamibiaNamibia, officially the Republic of Namibia , is a country in Southern Africa whose western border is the Atlantic Ocean. It shares borders with Angola and Zambia to the north, Botswana and Zimbabwe to the east, and South Africa to the south and east...
and a second it is new
Ausia-like genus from the Onega Peninsula,
White SeaThe White Sea is an inlet of the Barents Sea on the northwest coast of Russia. It is surrounded by Karelia to the west, the Kola peninsula to the north, and the Kanin Peninsula to the northeast....
of northern
RussiaRussia , officially known as both Russia and the Russian Federation , is a country in northern Eurasia . It is a semi-presidential republic, comprising 83 federal subjects...
. Results of new study have shown possible affinity of these Ediacaran organisms to the ascidians. These two organisms lived in the shallow waters of an sea, slightly more than 555-548 million years ago and are likely the oldest evidence of the chordate lineage of metazoans.
A Precambrian fossil known as
Yarnemia has been referred to the Urochordata, however this assignment is doubtful. Complete body fossils of tunicates are rare, but in some tunicate families, microscopic spicules are generated which may be preserved as microfossils. Such spicules have occasionally been described from Jurassic and later rocks. Few paleontologists are familiar with them; tunicate spicules may be mistaken for sponge spicules.
Invasive species
Over the past few years, urochordates (notably of the genera
DidemnumDidemnum is a genus of tunicates in the family Didemnidae. Some varieties of didemnum can be characterized as invasive species. This is particularly an issue off the east coast of the United States, where in early 2006 didemnum were estimated to inhabit more than 175 square kilometers of this...
and
StyelaPleurogona is an order of tunicates. One of the more invasive species of this order is the "stalked sea squirt" Styela clava . Another invasive genus include the "chain sea squirts or chain tunicates" of the genus Botrylloides and the "golden star tunicate" Botryllus schlosseri ....
) have been
invading'Invasive species' is a phrase with several definitions. The first definition expresses the phrase in terms of non-indigenous species that adversely affect the habitats they invade economically, environmentally or ecologically...
coastal waters in many countries, and are spreading quickly. These mat-like organisms can smother other sea life, have very few natural predators, and are causing much concern. They form colonies which are yellowish cream in color, and look like thick sponge-like masses that overgrow themselves on stationary objects on the sea floor such as gravel, mollusc shells, and possibly other encrusting species. These colonies are flexible, irregular, long, flat, and often exist as branched outgrowths projected from the surface. Some of the outgrowths result from the colony encrusting worm tubes or other cylindrical objects but many are solid with a firm gelatinous core. The individuals of the colony are called zooids and many zooids with individual siphonal openings cover the surface of the colony.
Transportation of invasive tunicates is usually in the ballast water or on the hulls of
shipA ship is a large vessel that floats on water. Ships are generally distinguished from boats based on size and passenger capacity. Ships may be found on lakes, seas, and rivers and they allow for a variety of activities, such as the transport of people or goods, fishing, entertainment, public...
s. Current research indicates that many tunicates previously thought to be indigenous to Europe and the Americas are, in fact, invaders. Some of these invasions may have occurred centuries or even millennia ago. In some areas, tunicates are proving to be a major threat to
aquacultureAquaculture is the farming of freshwater and saltwater organisms such as finfish, molluscs, crustaceans and aquatic plants. Also known as aquafarming, aquaculture involves cultivating aquatic populations under controlled conditions, and can be contrasted with commercial fishing, which is the...
operations.
The U.S.
Geological SurveyThe term geological survey can be used to describe both the conduct of a survey for geological purposes and an institution holding geological information....
, NOAA Fisheries, and the
University of Rhode IslandThe University of Rhode Island, commonly abbreviated as URI, is the principal public research university in the State of Rhode Island, with its main campus in Kingston area of South Kingston, and three other campuses located throughout the state, including Providence's Feinstein Campus, the...
are investigating this phenomenon as they have been spotted in 2004 in
Georges BankGeorges Bank is a large elevated area of the sea floor which separates the Gulf of Maine from the Atlantic Ocean and is situated between Cape Cod, Massachusetts and Cape Sable Island, Nova Scotia ....
. They requested that any information or sightings of these invading colonies be reported to USGS to aid in their investigation.
Medical uses
Tunicates contain a host of potentially useful
chemical compoundA chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
s, including:
- Didemnins, effective against various types of cancer
Cancer is a class of diseases in which a group of cells display uncontrolled growth , invasion , and sometimes metastasis...
, as antiviralAntiviral may refer to:*Antiviral drug*Antiviral protein*Antivirus software*Antiviral Therapy, an academic journal...
s and immunosuppressantAn immunosuppressant is any substance that performs immunosuppression of the immune system. They may either be exogenous, as immunosuppressive drugs, or endogenous, as e. g. testosterone...
s
- Aplidine
Aplidine is a compound found in tunicates which "shows promise in shrinking tumors in pancreatic, stomach, bladder, and prostate cancers."The specific marine organism is Aplidium albicans. Aplidine consists of peptide molecules. In addition to the cancers mentioned above it is also under...
, effective against various types of cancer
- Esteinascidin 743
Esteinascidin 743 is a chemical derivative found within the tissue of tunicates. The compound has shown promising results in the treatment of soft tissue sarcoma...
, effective against various types of cancer
In the May 2007 issue of The
FASEB Journal, researchers from
Stanford UniversityThe Leland Stanford Junior University, commonly referred to as Stanford University or Stanford, is a private research university located in Stanford, California, United States...
showed that tunicates can correct abnormalities over a series of generations, and they suggest that a similar regenerative process may be possible for humans. The mechanisms underlying the phenomenon may lead to insights about the potential of cells and tissues to be reprogrammed and regenerate compromised human organs. Gerald Weissman, editor-in-chief of the journal, said "This study is a landmark in regenerative medicine; the Stanford group has accomplished the biological equivalent of turning a sow's ear into a silk purse and back again."
As food
Various
AscidiaceaAscidiacea is a class in the Urochordata subphylum of sac-like marine invertebrate filter feeders. Ascidians are characterized by a tough outer "tunic" made of the polysaccharide tunicin, as compared to other tunicates which are less rigid.Ascidians are found all over the world, usually in shallow...
species are consumed as food around the world.
External links