Final answer:
Option (A), The trochophore larva is shared by several phyla within the superphylum Lophotrochozoa, including annelids and mollusks, and is significant for invertebrate phylogeny and classification.
Step-by-step explanation:
The distinctive type of larva shared by several phyla of invertebrates and considered to be important in phylogeny is the trochophore larva. This type of larva is characterized by two bands of cilia surrounding a top-like body and is a free-swimming larva. It is found in several phyla within the superphylum Lophotrochozoa which includes organisms with either a lophophore feeding apparatus or a trochophore larva. The presence of the trochophore larva in a group's life cycle is significant to its classification.
Organisms with trochophore larvae include annelids and mollusks, suggesting a common ancestry among these and other related groups. Although some phyla classified as Lophotrochozoans, such as flatworms from Phylum Platyhelminthes, lack trochophore larvae, their placement within this superphylum is fortified by molecular analyses, such as ribosomal RNA sequencing.