Figure 31.7 Rotifers and Gastrotrichs (A) The rotifer diagrammed here reflects the general structure of many rotifers. (B) A micrograph reveals the internal complexity of the microscopic rotifers. (C) Spiny-headed worms are parasitic rotifer relatives. The spines of the proboscis anchor the animal to the organs of its host. (D) Gastrotrichs superficially resemble rotifers but have flattened ventral surfaces covered with cilia, as flatworms do.