Ascidiacea
Ascidiacea, commonly known as sea squirts or tunicates, are a class of marine invertebrate animals that belong to the subphylum Tunicata. They are filter feeders and are found in a wide range of marine environments, from shallow coastal waters to the deep sea. Ascidiacea are sessile organisms, meaning they are attached to a substrate and cannot move freely. They are also known for their unique ability to regenerate lost parts of their bodies.
Characteristics
Ascidiacea are characterized by their sac-like bodies, which are covered in a tough, leathery tunic made of cellulose. They have two siphons, one for inhaling water and the other for expelling water. The water is filtered through a pharynx lined with cilia, which trap food particles. Ascidiacea are also characterized by their simple nervous system, which consists of a single ganglion and a few nerves.
Environments
Ascidiacea are found in a variety of marine environments, including:
- Intertidal zones
- Rocky shores
- Coral reefs
- Seagrass meadows
- Deep sea
Life Cycle
Ascidiacea have a complex life cycle that includes both a sessile adult stage and a free-swimming larval stage. The larval stage is characterized by a tadpole-like shape with a tail containing a notochord. This notochord is a defining characteristic of the phylum Chordata, which includes vertebrates. After a period of free-swimming, the larva settles on a substrate and undergoes metamorphosis to become a sessile adult.
Classification
Ascidiacea are classified into three orders:
- Aplousobranchia: These are the most common order of ascidians and are characterized by having a simple internal structure. They are often found in colonies.
- Phlebobranchia: This order of ascidians is characterized by having a more complex internal structure than aplousobranchs. They are often found in solitary forms.
- Stolidobranchia: This order of ascidians is characterized by having a very complex internal structure and are often found in both solitary and colonial forms.
References
National Center for Biotechnology Information (NCBI): Ascidiacea