Marine inverts cover the cleaning crew, the ornamentals, and the predators. Cleaner shrimp (Lysmata amboinensis), peppermint shrimp, fire shrimp, harlequin shrimp, hermit crabs (blue-leg, red-leg, scarlet, electric blue), snails (turbo, trochus, cerith, nassarius, astraea, conch), starfish (sand-sifter, brittle, fromia, linckia), urchins (tuxedo, pencil, longspine), sea cucumbers (tiger tail, pink + black), sea hares, ornamental crabs (emerald mithrax, sally lightfoot, decorator, porcelain), and lobsters (purple reef, blue spotted).
The cleanup crew runs the unsexy but critical infrastructure of a healthy reef. Snails graze film algae and detritus. Hermits scavenge dropped food. Cerith and nassarius snails work the sand bed. A balanced cleanup crew (one snail per 2-3 gallons, plus a handful of hermits and a sand-sifter) processes the constant detritus production that biological filtration alone struggles with.
Sensitive marine inverts (cleaner shrimp, harlequin shrimp, ornamental starfish) demand mature systems with established live rock, microfauna, and 6+ months of stable operation. Adding them to a 60-day-old tank is an expensive mistake.
Roughly 25-30 snails (mix of turbo, trochus, cerith, nassarius), 5-10 hermit crabs (blue-leg or scarlet), 1-2 cleaner shrimp, and optionally a sand-sifting starfish or conch if your sand bed is established.
Most are. Avoid common chocolate chip stars (Protoreaster) - they eat coral. Linckia and Fromia are reef-safe but specialist feeders that often starve in tanks under 100 gallons. Sand-sifting stars (Archaster) eat sand-bed microfauna and starve smaller systems.
Yes, drip acclimate marine inverts for 60-90 minutes minimum. They're extremely sensitive to specific gravity swings - a 0.001 SG difference can shock them.