The intake openings are fairly wide, I lost a ritteri anemone to mine but to be fair, a friend bought an anemone the same day I did and lost it to Apex pumps which have much smaller openings. They do include a sock to put over the intake to protect animals, it is fairly fine and will clog if their is fine debris. About 10% of the flow is drawn through the bottom of the pump, the rest is drawn from the main intake. It spins backwards for some seconds every day to back flush the intake, this works perfectly on macro algae as I have a lot of plant life in my tank and anything on it is gone by the next day though unless the filter gets it, it may be back later. For fish, it has a safety by resistance and stops if something hits the prop, realistically this works well for fingers, crabs, snails and maybe big fish, but a small goby or wrasse would be done for, it stops in a millisecond but it has to be enough resistance, an anemone is not enough to stop it.