various sizes
Benefits:
Algae Control: They eat film algae, diatoms, and cyanobacteria, helping keep rocks and glass clean. 
Hard-to-Reach Areas: Their slug-like bodies and small, flat shells let them slip into tight crevices around corals that other cleanup crew members cannot reach.
Self-Sustaining: They breed easily in captivity through broadcast spawning, meaning a small group can establish a lasting, self-replenishing population. 
Smart Defense: If threatened by a predator, they can drop their tail (like a lizard) to distract the danger and escape.
Limitations:
Diet Limits: They will not eat large nuisance pests like green hair algae (GHA) or macroalgae.
Nocturnal Nature: They are mostly active at night, so you might not see them grazing during the day.
Predators: Fish like sixline wrasses or certain shrimp may hunt and eat them.