Phallusia fragilis is a species of solitary tunicate belonging to the family Ascidiidae. It is commonly known as the “fragile sea squirt,” and its translucent, gelatinous body makes it a fascinating sight for divers and marine enthusiasts alike.
Description & Characteristics
Phallusia fragilis is a solitary tunicate, meaning it exists as an individual, unlike its colonial counterparts. It is characterized by its soft, transparent body with a sac-like appearance. Its size typically ranges between 2 and 5 centimeters, with the largest specimens reaching up to 10 centimeters. It has a distinct siphon for both inhalant and exhalant water flow, allowing it to filter feed efficiently. The body’s exterior is covered in a thin tunic, a protective outer layer composed of cellulose, which is unique to tunicates. This tunic is remarkably fragile, hence the species’ common name, “fragile sea squirt.”
Habitat and Occurrence
Phallusia fragilis is a common inhabitant of the intertidal zone and shallow subtidal regions, with a depth range extending up to 50 meters. It is often found attached to rocky surfaces, seaweeds, and other marine organisms. This species is prevalent in temperate waters, primarily in the northeastern Atlantic Ocean, the Mediterranean Sea, and the Black Sea. Its distribution reflects its preference for moderate water temperatures and the presence of suitable substrata for attachment.
Taxonomy
Phallusia fragilis belongs to the Class: Ascidiacea, Order: Phlebobranchia, and Family: Ascidiidae. It is classified within the Phylum Chordata, indicating its evolutionary relationship to vertebrates, despite its seemingly simple form. The Ascidiacea, or sea squirts, are a diverse group of filter-feeding marine invertebrates that are characterized by their sac-like body and their sedentary lifestyle.
Feeding
Phallusia fragilis is a filter feeder, relying on a continuous flow of water through its siphons to capture microscopic food particles. As water enters through the inhalant siphon, it passes through a complex filtration system within the body. This system, known as the branchial sac, is lined with cilia that create a current and trap microscopic algae, bacteria, and other organic matter. The filtered water is then expelled through the exhalant siphon, leaving behind the captured food particles. This feeding strategy allows Phallusia fragilis to thrive in its rich marine environments.
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