Question

What are parapodia?

Answer 1

Hint: Parapodia are found in phylum Annelida. Phylum Annelida includes around 9000 species of animals that are metamerically segmented animals and possess a true coelom. These are triploblastic and bilaterally symmetrical animals with an organ-system grade of organization.

Complete answer:
Let us break down the word to understand its meaning. Para refers to beside or beyond whereas podia refer to feet, so in all parapodia refers to lateral protrusions. These Parapodia are locomotory organs that are used for movement from one place to another.

Parapodia are the organs that are a characteristic feature of Polychaeta that comes under phylum Annelids. These possess well-developed parapodia with a number of setae. They undergo indirect development which means the presence of metamorphosis with a free-swimming trochophore larva. Some examples are Nereis (Clam worm or sandworm or ragworm), Aphrodite (sea mouse), Arenicola (lugworm) and many more.

Additional information: The body of Annelids is covered in the definite cuticles that is secreted from the ectoderm. Their body wall possesses both circular and longitudinal muscles. At the time of locomotion, these muscles contract alternatively against the fluid-filled septate coelom. Also during locomotion bristles or setae present on the lower side of the body help to have a strong grip on the ground. Annelids possess a true coelom i.e. a fluid-filled body cavity with a gut. Transport of body fluids and discharge of gametes is done through the coelom which also acts as the hydrostatic skeleton.

Note:
- Parapodia have unjointed paired extensions of the body wall that are often missing in the major groups of Annelids but is a staple for the Polychaeta.
- Parapodia are like lateral extensions or protrusions of the foot that will act as fins for swimming in sea slugs or other molluscs.