Final answer:
Rotifers are not single-celled; they are complex, multicellular organisms that belong to phylum Rotifera, thus the correct answer is B) False.
Step-by-step explanation:
The statement that members of phylum Rotifera are single-celled organisms is false. Rotifers are actually microscopic, multicellular organisms, most of which are aquatic and can range in size from approximately 100 µm to 2 mm. These fascinating creatures are divided into three classes: Bdelloidea, Monogononta, and Seisonidea, with Bdelloidea rotifers exhibiting parthenogenetic reproduction. Rotifers are recognized for their ciliated, wheel-like structure called the corona, which they use for feeding, and a complex internal anatomy including a mastax, a pseudocoelom, and a segmented body consisting of a head, trunk, and foot. Despite their size, similar to Paramecium, rotifers have a complete digestive system and are capable of complex movements and behaviors.