Put it in a potato cannon, get two optic eye beams, record the time as the anemone flies through each beam. Tricky to get the path right, I am sure, trial and error will help. Then, time in seconds, say from an internal clock on whatever device gets the signal from the beams. So b1 is beam one, and the first the anemone passes through, then you have b2 for beam two. Measure the distance (d) in feet between the beams along the flight path. So, t1 is time b1 triggers, t2 for b2 trigger. Elapsed time, et, is t2-t1. Velocity is d/et, giving feet per second.
Put it in a potato cannon, get two optic eye beams, record the time as the anemone flies through each beam. Tricky to get the path right, I am sure, trial and error will help. Then, time in seconds, say from an internal clock on whatever device gets the signal from the beams. So b1 is beam one, and the first the anemone passes through, then you have b2 for beam two. Measure the distance (d) in feet between the beams along the flight path. So, t1 is time b1 triggers, t2 for b2 trigger. Elapsed time, et, is t2-t1. Velocity is d/et, giving feet per second.