Explanation
The correct answer is B: Nephridia.
Annelids are a phylum of segmented worms that are characterized by the presence of nephridia. Nephridia are excretory organs that filter waste products from the coelomic fluid and release them outside the body. This is a unique feature of annelids and is not found in other invertebrate phyla.
While some annelids are hermaphroditic, meaning they have both male and female reproductive organs, this is not a unique feature of the phylum. Hermaphroditism is also found in other invertebrate and vertebrate groups.
Annelids do have a true coelom, which is a body cavity that is completely lined with mesoderm. This allows for greater internal complexity and specialization of organs. However, a true coelom is not a unique feature of annelids and is also found in other invertebrate and vertebrate groups.
Finally, while the alimentary canal of annelids is complete, meaning it has a mouth and an anus, this is also not a unique feature of the phylum. A complete digestive system is found in many other invertebrate and vertebrate groups as well.
