Thaliacea
Encyclopedia
The Thaliacea comprise a class of marine animals within the subphylum Tunicata
. Unlike their bottom-dwelling relatives the ascidians
, thaliaceans are free-floating for their entire lifespan. The group includes both solitary and colonial
species.
s. They 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.
There are three orders of Thaliacea. Pyrosome
s are colonial animals, with multiple tiny zooid
s arranged in a cylinder closed at one end. All of the atrial siphons point inwards, emptying into a single, common cloaca
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.
Doliolid
s and salp
ids alternate between solitary and colonial life stages. Salp colonies can be several meters in length. Doliolids and salps rely on muscular action to propel themselves through surrounding sea water.
Thaliceans have a complex life cycle. Eggs hatch into an individual called a tadpole larva, which is the common larval stage for all Urochordates. This then develops into an oozoid, which reproduces asexually
by budding to produce a number of blastozoids. The individual blastozoids then reproduce sexually to produce the eggs and the next generation of tadpole larvae, which develop into oozoids.
Class Thaliacea
Tunicate
Tunicates, also known as urochordates, are members of the subphylum Tunicata, previously known as Urochordata, a group of underwater saclike filter feeders with incurrent and excurrent siphons that is classified within the phylum Chordata. While most tunicates live on the ocean floor, others such...
. Unlike their bottom-dwelling relatives the ascidians
Ascidiacea
Ascidiacea is a class in the Tunicata 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...
, thaliaceans are free-floating for their entire lifespan. The group includes both solitary and colonial
Colony (biology)
In biology, a colony reference to several individual organisms of the same species living closely together, usually for mutual benefit, such as stronger defense or the ability to attack bigger prey. Some insects live only in colonies...
species.
Anatomy
All of the thaliceans are filter feederFilter feeder
Filter 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, baleen whales, and many fish and some sharks. Some birds,...
s. They 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
Pharynx
The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...
. 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
Atrium (architecture)
In modern architecture, an atrium is a large open space, often several stories high and having a glazed roof and/or large windows, often situated within a larger multistory building and often located immediately beyond the main entrance doors...
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
Mucus
In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...
slowly pulled across the slits by cilia.
There are three orders of Thaliacea. Pyrosome
Pyrosoma
Pyrosomes, genus Pyrosoma, are free-floating colonial tunicates that live usually in the upper layers of the open ocean in warm seas, although some may be found at greater depths. Pyrosomes are cylindrical or conical shaped colonies made up of hundreds to thousands of individuals, known as zooids...
s are colonial animals, with multiple tiny zooid
Zooid
A zooid or zoöid is a single animal that is part of a colonial animal. The zooids can either be directly connected by tissue or share a common exoskeleton...
s arranged in a cylinder closed at one end. All of the atrial siphons point inwards, emptying into a single, common cloaca
Cloaca
In zoological anatomy, a cloaca is the posterior opening that serves as the only such opening for the intestinal, reproductive, and urinary tracts of certain animal species...
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.
Doliolid
Doliolida
Doliolida are small marine animals of the Tunicata phylum, related to salps and pyrosomas. The 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...
s and salp
Salp
A salp or salpa is a barrel-shaped, planktonic tunicate. It moves by contracting, thus pumping water through its gelatinous body...
ids alternate between solitary and colonial life stages. Salp colonies can be several meters in length. Doliolids and salps rely on muscular action to propel themselves through surrounding sea water.
Thaliceans have a complex life cycle. Eggs hatch into an individual called a tadpole larva, which is the common larval stage for all Urochordates. This then develops into an oozoid, which reproduces asexually
Asexual reproduction
Asexual reproduction is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only, it is reproduction which does not involve meiosis, ploidy reduction, or fertilization. A more stringent definition is agamogenesis which is reproduction without...
by budding to produce a number of blastozoids. The individual blastozoids then reproduce sexually to produce the eggs and the next generation of tadpole larvae, which develop into oozoids.
The jelly pump and the carbon cycle
Thaliaceans are 30% carbon by mass. Therefore their dense bodies sink to the bottom of the oceans when they die 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, each containing a single family:Class Thaliacea
- Order PyrosomidaPyrosomaPyrosomes, genus Pyrosoma, are free-floating colonial tunicates that live usually in the upper layers of the open ocean in warm seas, although some may be found at greater depths. Pyrosomes are cylindrical or conical shaped colonies made up of hundreds to thousands of individuals, known as zooids...
- Family PyrosomatidaePyrosomaPyrosomes, genus Pyrosoma, are free-floating colonial tunicates that live usually in the upper layers of the open ocean in warm seas, although some may be found at greater depths. Pyrosomes are cylindrical or conical shaped colonies made up of hundreds to thousands of individuals, known as zooids...
- Genus PyrosomaPyrosomaPyrosomes, genus Pyrosoma, are free-floating colonial tunicates that live usually in the upper layers of the open ocean in warm seas, although some may be found at greater depths. Pyrosomes are cylindrical or conical shaped colonies made up of hundreds to thousands of individuals, known as zooids...
- Genus Pyrostremma
- Genus Pyrosoma
- Family Pyrosomatidae
- Order DoliolidaDoliolidaDoliolida are small marine animals of the Tunicata phylum, related to salps and pyrosomas. The 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...
- Family DoliolidaeDoliolidaDoliolida are small marine animals of the Tunicata phylum, related to salps and pyrosomas. The 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...
- Genus Anchina
- Genus DoliolettaDoliolettaDolioletta 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...
Borgert, 1894 - Genus Doliolina Garstang, 1933
- Genus Dolioloides Garstang, 1933
- Genus DoliolumDoliolumDoliolum 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: *Doliolum denticulatum Quoy & Gaimard, 1834...
Quoy & Gaimard, 1834 - Genus Doliopsis
- Family Doliolidae
- Order Salpida
- Family Salpidae - salps
- Genus Brooksia
- Genus Cyclosalpa
- Genus Helicosalpa
- Genus Ihlea
- Genus Pegea
- Genus Ritteriella
- Genus Salpa
- Genus Soestia
- Genus Tetys
- Genus Thalia
- Genus Traustedtia
- Genus Weelia
- Family Salpidae - salps