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Home › Sea Life Facts › Marine Species › Invertebrates › Tunicata

Interesting Facts about Sea Squirts

[Sea Squirt Phylum: Chordata] [Subphylum: Tunicata (Urochordata)] [Class: Ascidiacea]

The sea squirt classification contains about three thousand (3,000) recognised species (class Ascidiacea), with new members still being discovered in deep ocean environments worldwide.

This section contains information about sea squirt tunicates, including where they live, what they feed on, and how these fascinating marine invertebrates reproduce.

Sea Squirt Animal Habitats and Distribution

So, what is a sea squirt and where do most types of sea squirts live?

Imagine a sea animal that squirts water, and one that belongs with the subphylum Tunicata (Urochordata).

Then...

Consider the presence of the sea squirt notochord (a rod-like structure) that puts it within the phylum Chordata.

In other words:

Even though adult sea squirts are marine invertebrates, the taxonomy also includes a comprehensive list of vertebrates, such as birds, fishes, reptiles, and Homo sapiens (humans).

Pro Tip: The sea squirt scientific name is Ascidiacea (or sessile "ascidians") - the most described and documented class of tunicates. But, the species also contains several other common names, such as sea pork, sea tulips, and sea livers.

Cosmopolitan Distribution

The sea squirt species inhabits all oceans around the world, from the Arctic Ocean down to the Antarctic. Moreover, they can survive in a wide range of depths.

For example, they live in shallow intertidal zones and even in deep seas at depths approaching several thousand of metres below the surface.

But, sea squirts tend to grow in superabundance in shallow coastal waters that contain solid structures so they can attach themselves to them, such as:

• Boulders and rocks
• Coral reef formations
• Dock pilings
• Sunken shipwrecks

As a consequence of that, you can also find these sessile creatures living in harbors and marinas. They will tolerate cold and warm water environments, including those with low salinity (e.g. brackish river estuaries).

Sea Squirt Characteristics

It is fair to describe the sea squirt species as a diverse family. But, they share several common traits and physical features that unite the entire classification.

For example, all adult ascidian tunicates are "sessile" creatures that remain attached to an object directly by the base - somewhere close to the ocean floor.

But wait - there's more:

They also share the same hollow, bag-shaped leathery body structure (globular and flexible) made of tunicin, with two (2) siphons (incurrent and excurrent).

It is also rare to find any tunicate sea squirt that doesn't display a distinctive combination of colours and patterns, especially a mixture of yellows, reds, white, purple, and brown.

Nonetheless, some are translucent with very little or no colouration at all, the solitary sea squirt (Ciona savignyi), for example.

Sea Squirt Size

Even though size varies throughout the species, one of the smallest is the colonial light-bulb sea squirt, measuring less than two (2) centimetres high.

However, one of the biggest is the "Large Sea Squirt" which can grow up to twenty (20) centimetres tall (8 inches).

Note: The colonial sea squirts (zooids) often encrust large surfaces to form 'mats' as they grow horizontally over rocks and rigid structures.

What Do Sea Squirts Eat?

Tunicates are filter-feeders that use a pharyngeal mucous basket or net to strain planktonic organisms and extract other types of detritus from water, including microscopic zooplankton and bacteria.

As a result of several feeding adaptations, many of the colonial sea squirt species have become efficient consumers and are able to filter huge amounts of water.

Whereas, the deep-sea variations tend to be suspension feeders that depend on particulate matter being available above them in the water column.

Interesting Fact: When sea squirts remove bacteria, plankton, and types of decaying organic matter, it helps to clean the water in the oceans. Hence, tunicates have an important role in aquaculture water quality and ecosystem health.

Sea Squirts Species List

How Do Sea Squirts Reproduce?

In general, sea squirt reproduction, and the associated reproductive strategies, depends on the actual species, meaning whether they are solitary or colonial (zooid).

Even so, because most are hermaphroditic (e.g. male and female sexual reproduction), the individuals produce eggs and sperm and release them into the open water for external fertilisation.

However...

Asexual fertilisation (known as budding) occurs inside the body for some of the colonial species. The sea squirt larvae are kept inside (brooded) until they have developed enough for release.

The free-swimming larva resembles tiny tadpoles, with a notochord and a tail (hence their evolutionarily link to vertebrates).

Within a few short hours, they reabsorb the notochord, attach themselves to a solid object, and begin their new life as sessile adults.

Tunicates Threats and Predators

In general, a sea squirt life cycle can last between a few months and several years. Despite the strong, external flexible covering (tunic) made of cellulose, they face a number of natural and human-related threats.

In the wild, sea squirts are part of the daily diet for marine species that are able to pierce the tough tunic - and digest it. Typical examples include:

• Crabs
• Lobsters
• Pufferfish
• Sea snails
• Sea urchins
• Starfish
• Wrasses

Even though some humans eat sea squirts in some countries (e.g. Korea, Japan), some species produce a toxic chemical that is considered unsafe for human consumption.

In addition, some of the major factors for a decline in certain regions include other types of human behaviour (e.g. coral reef destruction and degradation, overfishing, invasive species of tunicates, and warming seas).

Interesting Fact: The IUCN Red List of Endangered Species has limited data on the conservation status of sea squirts (Ascidiacea). However, the general view is that most are not currently considered as being threatened or endangered.

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