Which part of the water do lancelets inhabit?

Lower bottom part

Lancelets are aquatic animals which are slender in shape and they look like fish without eyes. They have body that is tapered at both sides. These animals feed upon the debris suspended from the entire aquatic  environment. They remain partially buried in the water bed. They use hair like tentacles to grab food from debris. These animals lives in lower bottom part of water.

the answer is "a.) well–developed vascular system."

explanation:

igneous rocks which formed by the crystallization of magma at the surface of the earth called extrusive rocks. they are characterized by fine-grained textures because the rapid cooling at or near the surface did not provide enough time for large crystals to grow.