Hydra: Dangers to Fry and Small Fish Hydras ... However, they can be threatened by planaria, flatworms with arrow-shaped heads. Planaria are most likely to eat baby shrimp or those that have ...

Planarian flatworms regenerate their heads and tails after amputation. It turns out that they use Wnt–β-catenin signalling to determine where the head and the tail should form. Figure 1: Wnt ...