The Obese Ascidian, scientifically known as Phallusia obesa, is a fascinating marine invertebrate belonging to the tunicate family. Its unique characteristics and distribution make it an intriguing subject of study in marine biology.
Description & Characteristics
Phallusia obesa, true to its name, is a relatively large ascidian, reaching a maximum size of about 10 centimeters in length. Its body is typically oval-shaped, with two siphons located at one end: an incurrent siphon for drawing in water and an excurrent siphon for expelling filtered water. The outer tunic, which gives ascidians their common name of “sea squirts,” is usually rough and leathery in texture, providing protection and structural support.
Habitat and Occurrence
The Obese Ascidian, Phallusia obesa, is a common sight in various coastal regions, particularly in the Mediterranean Sea and the North Atlantic Ocean. It typically inhabits rocky substrates and seagrass beds, often found attached to hard surfaces in intertidal zones and shallow subtidal areas. This species thrives in the infralittoral zone, which encompasses the region from low tide to the depth where light starts to dim significantly.
Taxonomy
Phallusia obesa is classified within the phylum Chordata, a group that includes all vertebrates. This species belongs to the Class: Ascidiacea, which encompasses all sea squirts. It is further classified within the Order: Phlebobranchia, a group characterized by simple gill slits and a single row of tentacles surrounding the incurrent siphon. Finally, Phallusia obesa belongs to the Family: Ascidiidae, a diverse family of solitary ascidians.
Feeding
Phallusia obesa is a filter feeder, relying on plankton as its primary food source. Water is drawn into the incurrent siphon, passing through a complex system of gill slits where tiny food particles are trapped. The filtered water is then expelled through the excurrent siphon. This efficient feeding mechanism allows Phallusia obesa to thrive in environments rich in plankton, playing a crucial role in the marine food web.
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