This is a flagellated larva of Leucosolenia

The correct option is Parenchymula.

To understand why this is the correct answer, let's break down the life cycle and larval stages of the genus Leucosolenia:
1. Genus Classification: Leucosolenia is a genus of tubular, calcareous sponges belonging to the phylum Porifera.
2. Reproduction and Development: Sponges within this group undergo sexual reproduction where fertilization results in a zygote that develops into a free-swimming, flagellated larva.
3. Larval Identification: The characteristic flagellated larval stage of Leucosolenia is called a parenchymula (specifically, a coeloblastula-like stage that solidifies into a parenchymula, or is described classically as a parenchymula larva depending on the specific calcareous sponge details, with parenchymula being the standard option provided here). This larva is solid-bodied and covered with flagellated cells on the outer surface, allowing it to swim and disperse before settling down on a substrate to grow into a sessile adult sponge.

Let's examine the other options to see why they are incorrect:
- Maggot: This is the larval stage of insects, specifically flies (order Diptera), and is completely unrelated to sponges.
- Planula: This is the characteristic free-swimming, flat, ciliated larval stage of Cnidarians (such as jellyfish, corals, and sea anemones), not sponges.
- Kedia: This is not a recognized larval stage in the phylum Porifera or other major animal phyla.

Therefore, the flagellated larva of Leucosolenia is indeed the Parenchymula.