Phoronis

Phoronis is a genus of lophophorate marine worms belonging to the phylum Phoronida. These animals are tube-dwelling filter feeders found in coastal waters worldwide. They are characterized by their U-shaped digestive tract and a lophophore, a crown of ciliated tentacles used for capturing food particles from the water column.

Characteristics:

• Body Plan: Phoronids possess a cylindrical, elongated body that is typically concealed within a secreted chitinous tube. The body is divided into three regions: the epistome, the trunk, and the ampulla.
• Lophophore: The most distinctive feature of Phoronis is the lophophore. This horseshoe-shaped or spirally coiled structure bears numerous ciliated tentacles. The cilia create water currents that draw suspended particles towards the mouth, where they are captured and ingested.
• Tube: The secreted chitinous tube provides protection and support for the worm. The worm can retract into the tube when disturbed.
• Circulatory System: Phoronids have a closed circulatory system with blood vessels that transport oxygen and nutrients throughout the body.
• Nervous System: The nervous system consists of a nerve ring around the pharynx and a longitudinal nerve cord.
• Reproduction: Phoronids can reproduce both sexually and asexually. Asexual reproduction occurs through budding or fragmentation. Sexual reproduction involves the release of gametes into the water, where fertilization occurs. The larvae, known as actinotrocha larvae, are planktonic and undergo metamorphosis to transform into the adult form.

Habitat and Distribution:

Phoronis species are found in a variety of marine habitats, including intertidal zones, shallow subtidal areas, and deeper waters. They typically inhabit sandy or muddy substrates and are often found attached to rocks, shells, or other submerged objects. They have a global distribution, with species found in both temperate and tropical waters.

Taxonomy:

Phoronis is the type genus of the phylum Phoronida. The classification within the genus is based on morphological characteristics, such as the shape of the lophophore and the presence or absence of certain structures. Species identification can be challenging due to the subtle differences between species.