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Salp

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Salpida
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Subphylum:
Urochordata
Class:
Thaliacea
Order:
Salpida
Family:
Salpidae

A salp is a barrel-shaped, free-floating tunicate that moves by pumping water through its gelatinous body by means of contraction, and strains the water, feeding on phytoplankton.

Distribution

Salps are common in equatorial seas, where they float randomly alone or in long, stringy colonies. However, the most abundant concentrations of salps are in the Southern Ocean. Here they sometimes form enormous swarms, often in deep water, and are sometimes even more abundant than krill. In the last century, while krill populations in the Southern Ocean declined, salp populations appear to be increasing.

File:Salp-RedSea.JPG
A string of salp in the Red Sea

One reason for the success of salps is how they respond to phytoplankton blooms. When there is plenty of food, salps can quickly bud off clones, which graze the phytoplankton and can grow at a rate which is probably faster than any other multicellular animal, quickly stripping the phytoplankton from the sea. However, if the phytoplankton is too dense, the salps can clog and sink to the bottom. During these blooms, beaches can become slimy with mats of salp bodies, and other planktonic species can experience fluctuations in their numbers due to competition with the salps.

Sinking fecal pellets and bodies of salps carry carbon to the sea floor, and salps are abundant enough to have an impact on the ocean's biological pump. Consequently, large changes in their abundance or distribution may alter the ocean's carbon cycle, and potentially play a role in climate change.

Nervous systems and Relationships

Salps are related to doliolida and pyrosoma.

Although salps seem similar to jellyfish because of the simple form of their bodies and their free-floating way of life, closer examination shows that their bodies have internal structure that is similar to the shape of animals with true backbones: salps are structurally most closely related to vertebrates.

Because their bodies appear to have a form preliminary to vertebrates, salps are used as a starting-point in models of how vertebrates evolved. Scientists speculate that the tiny groups of nerves in salps are one of the first instances of a primitive nervous system, which eventually evolved into the more complex central nervous systems of vertebrates.

Studies on salp brains have been undertaken by Thurston Lacalli and Linda Z. Holland and published in Philosophical Transactions of the Royal Society of London.

Classification

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