The carpet sea squirt is a filter feeder, taking in water through its ‘inhalant’ siphon and filtering out small food particles and plankton using mucous-covered gill slits (2) (3) (4) (7) (8). Tiny, beating hairs on the gills move food particles into the gut for digestion, and the gills are also used to extract oxygen from the water (7) (8).
Inside its body, the carpet sea squirt has a small, simple heart from which blood vessels run to its various organs (7) (8). A small ball of nerve cells serves as the animal’s brain (8).
Each of the carpet sea squirt’s zooids is hermaphroditic, possessing both male and female reproductive organs (3) (7) (8) (9). Some sea squirts release their eggs and sperm into the water column, where fertilisation occurs. However, in the carpet sea squirt the eggs are fertilised internally from sperm taken in through the inhalant siphon (7) (8), and the larvae are brooded inside the colony before being released into the water. The carpet sea squirt larva spends only a few hours in the water before settling head-down on a firm surface and transforming into a zooid (2) (3) (4) (5) (8) (9).
Sea squirts are unusual in that they are more closely related to vertebrates than to invertebrates, despite the adult sea squirt’s quite simple appearance and immobile lifestyle (7). The relationship to vertebrates is more closely seen in the sea squirt larvae, which resemble tiny tadpoles with a long tail, a nerve cord, and more developed internal organs than the adults (7) (8). When the tadpole settles and transforms into a zooid, its tail and nerve chord are absorbed into its body (8).
Newly transformed zooids go on to found a new colony by reproducing asexually, splitting into many new, genetically identical individuals (2) (3) (4) (5) (9). The colony grows rapidly and the young zooids can reach sexual maturity in just a few weeks (2). New carpet sea squirt colonies can also form by fragmentation, when a portion of the colony breaks off and reattaches in a new location (2) (3) (5) (9). These fragments may also contain larvae, which can help to spread the species even further (5).
In the carpet sea squirt, the production of larvae generally depends on the water temperature (3) (9), often occurring in spring and autumn (2). Colonies of this species survive year-round, but tend to shrink during the cold winter months (5) (9). Very few predators are known to feed on the carpet sea squirt, although it has reportedly been eaten by certain snails, sea urchins and sea stars (5) (9). Carpet sea squirt colonies have an acidic tunic and exude a toxic substance onto their surface, discouraging most predators and preventing other species from growing over them (2) (4) (5).