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Thaliacea

(Class)

Overview

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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.

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All of the thaliceans are filter feeders. 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. Pyrosomes are colonial animals, with multiple tiny zooids 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.

Doliolids and salpids 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.

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.[1]

Taxonomy

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The class is a relatively small one, and is divided into three orders, each containing a single family:

Class Thaliacea

External links

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al 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 di gestive 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. Pyrosomes are colonial animals, with multiple tiny zooids 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.

Doliolids and salpids 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.

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.[1]

Taxonomy

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The class is a relatively small one, and is divided into three orders, each containing a single family:

Class Thaliacea

External links

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References

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  1. ^ Thaliaceans and the carbon cycle
  2. ^ Doliolidae World Register of Marine Species. Retrieved 2011-11-17.

Taxonomy

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The Class Thaliacea is further organized into finer groupings including:

Orders

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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 of barrel bands. Like all tunicates, they are filter feeders. They are free-floating; the same forced flow of water through their body with which they gather plankton is used for propulsion - not unlike a tiny ramjet engine. Doliolids are capable of quick movement. They have a complicated life cycle consisting of sexual and asexual generations. They are nearly exclusively tropical animals, although a few species can be found as far to the north as North California. [more]

Pyrosomatida

[more]

Salpida

A salp (plural salps) or salpa (plural salpae or salpas) is a barrel-shaped, planktonic tunicate. It moves by contracting, thus pumping water through its gelatinous body. The salp strains the pumped water through its internal feeding filters, feeding on phytoplankton. [more]

At least 70 species and subspecies belong to the Order Salpida.

More info about the Order Salpida may be found here.

References

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  1. ^ Thaliaceans and the carbon cycle
  2. ^ Doliolidae World Register of Marine Species. Retrieved 2011-11-17.

Sources

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Last Revised: August 24, 2012
2012/08/24 13:06:58