The whorl needler split from its ancestor. The whorl needler is rather different from its ancestor: instead of dragging its four arms behind it, the whorl needler keeps them in front of itself for several reasons. The arms are used to impale swarmers and inject them with a toxic fluid that dissolves it from the inside and allows the whorl needler to drink the swarmers' innards. Another reason for the whorl needler to keep its arms in front of itself is that small, extremely sensitive membranes are attached to the arms - these are used for navigation. The needler can make a high pitched sound allowing the membranes to pick up vibrations in the water, allowing them to navigate via echolocation instead of swimming randomly around like its ancestor.