What Are Sea Salps?

Bbelonging to the Salpidae family, salps are barrel-shaped tunicate marine animals that float freely alone or in extensive colonies in the pelagic zone of the world's oceans. They have an almost global distribution within them. The term tunicates refers to the tough cellulose tunic that covers and protects these animals. In sea salps, this covering is transparent.

They belong to the phylum Chordata, but they present different characteristics in the larval stage and then lose most of them when undergoing metamorphosis. For example, the nerve cord present in larvae is reduced to a simple ganglion in adults. Young salps are known as blastozooids and lack the more complex reproductive and other organs of their adult form.

Learn more about another type of sometimes pelagic animal with our article on what are amphipods?

Now we know more about what they are, we can have a better idea of what they look like and how they function by looking at the characteristics of salps. Salps:

• Are barrel-shaped and their body is made up of a gelatinous and transparent covering known as a tunic.
• Measure from a few millimeters in length to several centimeters.
• Are distributed in the pelagic zone of equatorial, temperate and cold seas. Discover the types of pelagic fish in our guide to these animals.
• Have a nerve ganglion in the front part of their body and a horseshoe-shaped ‘eye’.
• Have two openings on their body, one oral and one cloacal.
• Have muscular bands on their mantle and their number varies depending on the species.
• Form a digestive tube that is coiled, making up part of a structure called the ‘nucleus’ (not to be confused with a cell nucleus).
• Has a circulatory system made up of a heart and two large vessels.
• Move through a contraction mechanism which creates one of the few true jet propulsion systems in animals.
• Are filter-feeding herbivores, pumping water through their gelatinous body and forcing its passage through internal filters. They feed on phytoplankton.
• Are usually found in low densities in the oceans, but when the concentration of phytoplankton increases they proliferate rapidly and their populations increase considerably.
• They are hermaphrodites and have a complex life cycle with alternating generations between aggregated forms and solitary forms. Older salps provide male gametes while the younger ones are female.
• Have luminous organs that emit bright lights. Learn more about how bioluminescence works in our related article.
• Are preyed upon by marine animals from the pelagic zone, such as turtles and fish (tuna and cod are some of their most common predators).
• Are vectors of marine toxins from phytoplankton, causing harmful effects on other marine animals, such as fish, reptiles, birds and mammals.
• Play an important role related to climate change since they can capture carbon dioxide.

Discover more about pelagic animals by learning the difference between a squid and a cuttlefish.

There are several species within the Salpidae family , let's get to know five of them:

Common Salp (Salpa fusiformis)

As we might be able to tell by its common name, the common salp is the most populous sea salp species found in the world's oceans, having a cosmopolitan distribution. Its body is asymmetrical and generally barrel- or spindle-shaped. It has a pale green core. They move vertically in the water column and approach the surface at night.

Pinnate Salp (Cyclosalpa pinnata)

The free forms of this species have an elongated, barrel-shaped body. Their tunic is thin and they can measure 75 mm each. In the colonial forms, the tunic is thicker than in the solitary form and can measure 56 mm. Within the Cyclosalpinae subfamily, it is the only species that presents luminous organs in their aggregate form. This is a characteristic of great importance that differentiates it from other types of sea salp species.

Salp chain (Thalia democratica)

With a thick and transparent tunic, T. democratica is a very abundant species frequently found in the Atlantic, Indian and Pacific oceans. It has even in the Mediterranean Sea. Its solitary shape measures approximately 15 mm and resembles a barrel. The aggregated colonial form has a rounded shape, its posterior part is pointed and its intestine forms a more compact nucleus than in the case of the free form.

Cylindrical salp (Weelia cylindrica)

As its name indicates, it has a cylindrical shape with a thin tunic. They generally have between eight and nine muscle bands. The aggregate shape of this species is oval with its maximum length being 16 mm. Unlike the free form, it has its oral and cloacal openings in the dorsal part of the body.

Colonial salp (Pegea confoederata)

This species distributed in warm and temperate seas reaches a length of 120 mm and its musculature is scarce. It only has four muscular bands on its body. The aggregate colonial form measures 154 mm and has musculature similar to the free-living form.

It is very likely that many people confuse salps with jellyfish due to their similar morphology. Especially if we see a single sea salp rather than a colony, it is easy to think of them as a type of jellyfish. Since jellyfish are known for their ability to sting, many wonder if salps are able to cause harm to humans in the same way. Salps do not sting. They are completely harmless in themselves and cannot attack a human. However, they can be a vector for toxins, as mentioned above.

We have explained what sea salps are and their characteristics, as well as the fact they are not jellyfish. Learn more about the latter animal with our guide to jellyfish anatomy.

If you want to read similar articles to What Are Sea Salps?, we recommend you visit our Wild animals category.