What group of aquatic (mostly marine) animals has a sac-like body plan that is asymmetric, has a single germ layer, and a cell level of organization with no true tissues? Hint These animals are sessile, suspension feeders, and reproduce both asexually (budding or fragmentation) and sexually (via eggs and sperms).

A. Cnidaria
B. Platyhelminthes
C. Porifera
D. Mollusca