The Thaliacea comprise a class of marine animals within the subphylum Tunicata. Unlike their

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

relatives the ascidians, thaliaceans are free-floating ( pelagic) for their entire lifespan. The group includes species with complex life cycles, with both solitary and

colonial Colonial or The Colonial may refer to: * Colonial, of, relating to, or characteristic of a colony or colony (biology) Architecture * American colonial architecture * French Colonial * Spanish Colonial architecture Automobiles * Colonial (1920 a ...

forms.

Anatomy

The three orders of thaliaceans are

filter feeder Filter feeders are a sub-group of suspension feeding 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 feedin ...

s. Pyrosomes are colonial animals, with multiple tiny ascidian-like zooids arranged in a cylinder closed at one end. All of the atrial siphons point inwards, emptying into a single, common

cloaca In animal anatomy, a cloaca ( ), plural cloacae ( or ), is the posterior orifice that serves as the only opening for the digestive, reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles and birds, a ...

in the centre of the cylinder. As the water exhaled by the zooids exits through a common opening, the water movement slowly propels the pyrosome through the sea. Salps and doliolids have a transparent barrel-shaped body through which they pump water, propelling them through the sea, and from which they extract food. The bulk of the body consists of the large pharynx. Water enters the pharynx through the large buccal siphon at the front end of the animal, and is forced through a number of slits in the pharyngeal wall into an atrium lying just behind it. From here, the water is expelled through an atrial siphon at the posterior end. The pharynx is both a respiratory organ and a digestive one, filtering food from the water with the aid of a net of mucus slowly pulled across the slits by

cilia The cilium, plural cilia (), is a membrane-bound organelle found on most types of eukaryotic cell, and certain microorganisms known as ciliates. Cilia are absent in bacteria and archaea. The cilium has the shape of a slender threadlike projecti ...

. Doliolids and salps alternate between asexual and sexual life stages. Salp colonies can be several meters in length. Doliolids and salps rely on muscular action to propel themselves through surrounding seawater. Thaliaceans have complex lifecycles. Doliolid eggs hatch into swimming tadpole larvae, which are the common larval stage for other

urochordates A tunicate is a marine invertebrate animal, a member of the subphylum Tunicata (). It 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 ...

. Pyrosomes are ovoviviparous, meaning the eggs develop inside the "mother" without the tadpole stage. Salps are viviparous, meaning the embryos are linked to the "mother" by a placenta. This then develops into an oozoid, which reproduces asexually by budding to produce a number of blastozoids, which form long chains (see image). The individual blastozoids then reproduce sexually to produce the eggs and the next generation of oozoids. The dorsal, hollow nerve cord and

notochord In anatomy, the notochord is a flexible rod which is similar in structure to the stiffer cartilage. If a species has a notochord at any stage of its life cycle (along with 4 other features), it is, by definition, a chordate. The notochord consis ...

found in

Chordata A chordate () is an animal of the phylum Chordata (). All chordates possess, at some point during their larval or adult stages, five synapomorphies, or primary physical characteristics, that distinguish them from all the other taxa. These fiv ...

has been lost, except for a rudimentary one in some doliolid larvae.

The jell pump and the carbon cycle

Thaliaceans play an important role in the ecology of the sea. Their dense faecal pellets sink to the bottom of the oceans, and this may be a major part of the worldwide carbon cycle.

Taxonomy

The class is a relatively small one, and is divided into three orders: Class Thaliacea
World Register of Marine Species. Retrieved 2014-02-13. * Order

Pyrosomida Pyrosomes, genus ''Pyrosoma'', are free-floating colonial tunicates that usually live in the upper layers of the open ocean in warm seas, although some may be found at greater depths. Pyrosomes are cylindrical or cone-shaped colonies up to long, ...

Jones 1848 ** Family

Pyrosomatidae Pyrosomes, genus ''Pyrosoma'', are free-floating colonial tunicates that usually live in the upper layers of the open ocean in warm seas, although some may be found at greater depths. Pyrosomes are cylindrical or cone-shaped colonies up to long, ...

Garstang 1929 ***Subfamily Pyrostremmatinae van Soest 1979 **** Genus '' Pyrostremma'' Garstang 1929 'Propyrosoma'' Ivanova-Kazas 1962***Subfamily Pyrosomatinae **** Genus ''

Pyrosoma Pyrosomes, genus ''Pyrosoma'', are free-floating colonial tunicates that usually live in the upper layers of the open ocean in warm seas, although some may be found at greater depths. Pyrosomes are cylindrical or cone-shaped colonies up to long, ...

'' Péron 1804 'Dipleurosoma'' Brooks 1906**** Genus '' Pyrosomella'' van Soest 1979 * Order Salpida emimyaria; Desmomyaria Uljanin 1884** Family Salpidae Franstedt 1885 ***Subfamily Cyclosalpinae Yount 1954 **** Genus ''

Cyclosalpa ''Cyclosalpa'' is a genus of salps, marine tunicates in the class Thaliacea The Thaliacea comprise a class of marine animals within the subphylum Tunicata. Unlike their benthic relatives the ascidians, thaliaceans are free-floating (pelagic ...

'' Blainville 1827 'Orthocoela'' Macdonald 1864; ''Pyrosomopsis'' Macdonald 1864**** Genus '' Helicosalpa'' Todaro 1902 ***Subfamily

Salpinae A salp (plural salps, also known colloquially as “sea grape”) or salpa (plural salpae or salpas) is a barrel-shaped, planktic tunicate. It moves by contracting, thereby pumping water through its gelatinous body, one of the most efficient ...

Lahille 1888 **** Genus ''

Brooksia ''Brooksia'' is a genus of fungi in the class Dothideomycetes. The relationship of this taxon to other taxa within the class is unknown ('' incertae sedis''). The genus name of ''Brooksia'' is in honour of Frederick Tom Brooks (1882 – 1952), ...

'' Metcalf 1918 **** Genus ''

Iasis In Greek mythology, Iasis (Ancient Greek: Ἴασις means 'healing, remedy') was one of the Ionides Nymph, nymphs whose spring waters were believed to cure diseases. She was an Ancient Elis, Elean naiad-daughter of the Potamoi, river-god Cytherus ...

'' Savigny 1816 'Weelia'' Yount 1954; ''Salpa'' (''Iasis'') Savigny 1816**** Genus ''

Ihlea ''Ihlea'' is a genus of tunicates A tunicate is a marine invertebrate animal, a member of the subphylum Tunicata (). It is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords (including verteb ...

'' Metcalf 1919 non Metcalf 1918 'Apsteinia'' Metcalf 1918 non Schmeil 1894**** Genus '' Metcalfina'' Ihle & Ihle-Landenberg 1933 **** Genus ''

Pegea ''Pegea'' is a genus of tunicates belonging to the family Salpidae. The genus has almost cosmopolitan distribution. Species: *''Pegea bicaudata'' *''Pegea confoederata'' *''Pegea socia ''Pegea'' is a genus of tunicates belonging to the fa ...

'' Savigny 1816 **** Genus '' Ritteriella'' Metcalf 1919 'Ritteria'' Metcalf 1918 non Kramer 1877**** Genus '' Salpa'' Forskål 1775 'Biphora'' Bruguière 1789; ''Bifora'' Agassiz 1846; ''Dagysa'' Banks & Solander 1773**** Genus ''

Soestia ''Soestia'' is a monotypic genus of tunicates A tunicate is a marine invertebrate animal, a member of the subphylum Tunicata (). It is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords (incl ...

'' 'Holothurium'' sensu Pallas 1774**** Genus ''

Thetys Thetis (; grc-gre, Θέτις ), is a figure from Greek mythology with varying mythological roles. She mainly appears as a sea nymph, a goddess of water, or one of the 50 Nereids, daughters of the ancient sea god Nereus. When described as ...

'' Tilesius 1802 'Salpa'' (''Thetys'') Tilesius 1802**** Genus ''

Thalia Thalia, Thalía, Thaleia or Thalian may refer to: People * Thalia (given name), including a list of people with the name * Thalía (born 1971), Mexican singer and actress Mythological and fictional characters * Thalia (Grace), one of the three ...

'' Blumenbach 1798 'Dubreuillia'' Lesson 1832; ''Edusa'' Gistl 1848**** Genus '' Traustedtia'' Metcalf 1918 'Salpa'' (''Traustedtia'') Metcalf 1918* Order Doliolida yclomyaria Uljanin 1884**Suborder Doliolidina *** Family

Doliolidae Doliolidae is a family of tunicates in the order Doliolida. Members of the family are pelagic and often found far away from coastlines.

Bronn 1862 **** Genus ''

Dolioletta ''Dolioletta'' is a genus of tunicates in the family Doliolidae. Characteristics Members of the genus ''Dolioletta'' are transparent, gelatinous barrel-shaped animals, usually less than one centimetre long. They move in jerks by contracting the ...

'' Borgert 1894 **** Genus ''

Doliolina ''Doliolina'' is a genus of tunicates belonging to the family Doliolidae Doliolidae is a family of tunicates in the order Doliolida. Members of the family are pelagic and often found far away from coastlines.Dolioloides'' Garstang 1933 **** Genus ''

Doliolum ''Doliolum'' is a genus of tunicates, the members of which move via jet propulsion. A detailed description can be found at . Species The World Register of Marine Species lists the following species:Doliopsoididae Doliopsoididae is a family of tunicates belonging to the order Doliolida The Doliolida are an order of small marine animals of the subphylum Tunicata. They are in the class Thaliacea, which also includes the salps and pyrosomes. The doliol ...

Godeaux 1996 **** Genus '' Doliopsoides'' Krüger 1939 **Suborder Doliopsidina *** Family

Doliolunidae Doliolunidae is a family of tunicates belonging to the order Doliolida The Doliolida are an order of small marine animals of the subphylum Tunicata. They are in the class Thaliacea, which also includes the salps and pyrosomes. The doliolid ...

Robison, Raskoff & Sherlock 2005 **** Genus '' Pseudusa'' Robison, Raskoff & Sherlock 2005 *** Family

Doliopsidae Doliopsidae is a family of tunicates belonging to the order Doliolida The Doliolida are an order of small marine animals of the subphylum Tunicata. They are in the class Thaliacea, which also includes the salps and pyrosomes. The doliolid ...

Godeaux 1996 **** Genus '' Doliolula'' Robison, Raskoff & Sherlock 2005 **** Genus ''

Doliopsis ''Doliopsis'' is a genus of tunicates belonging to the family Doliopsidae Doliopsidae is a family of tunicates belonging to the order Doliolida The Doliolida are an order of small marine animals of the subphylum Tunicata. They are in the ...

'' Vogt 1854 *** Family

Paradoliopsidae Paradoliopsidae is a family of tunicates belonging to the order Doliolida The Doliolida are an order of small marine animals of the subphylum Tunicata. They are in the class Thaliacea, which also includes the salps and pyrosomes. The doli ...

Godeaux 1996 **** Genus '' Paradoliopsis'' Godeaux 1996

References

* *

External links

earthlife.net
{{Taxonbar, from=Q610887 Thaliacea, Chordate classes