Marine aquarium invertebrates

Marine invertebrates run from the reef clean-up crew to centerpiece animals in their own right: cleaner shrimp, snails and hermit crabs that handle algae and detritus, plus anemones, clams, urchins and stars. Each profile lists what the species needs and whether it is safe in a reef.

Tank size: 5–201 gal; 5 gal (20 L) to 201 gal (760 L); half the list needs 20 gal (75 L) or more
Temperature: 75–81°F; 24–27°C, most of the list
pH: 8.1–8.4; Most of the list
Difficulty: 60 easy; 30 medium · 28 difficult
Temperament: 94 peaceful; 18 mostly peaceful · 6 aggressive
Reef safety: 59 reef safe; 48 reef safe with caution · 11 not reef safe

118 species and 4 varieties

Start here

The marine inverts to start with

The skunk cleaner shrimp is marked beginner at 2.4 inches (6 cm) for 20 gallons (75 liters), and it cleans the fish and the hand that feeds it. The trochus snail is the grazer marked beginner, and the blue-leg hermit crab the scavenger, both for 11 gallons (40 liters). The bubble tip anemone is the host anemone with a track record, marked medium for 30 gallons (115 liters). The derasa clam is the giant clam marked beginner, a sand-bed clam for 40 gallons (150 liters). The tuxedo urchin grazes algae at 3.1 inches (8 cm) for 20 gallons (75 liters), marked easy, and carries a caution only because it carries frags around on its back.

The rule

What the reef marks mean for invertebrates

Every profile carries a reef mark. Reef safe means the animal does not eat coral as a matter of course. Reef-safe hermits can still kill a snail for its shell unless you keep spare shells in the tank. The peppermint and fire shrimp are marked reef safe but may pick at coral polyps when underfed. Caution covers habits like an urchin carrying frags, a hungry crab picking at polyps or a starfish eating sleeping fish. Not reef safe means it eats coral, fish or other invertebrates, the chocolate chip star and the peacock mantis shrimp among them. The green sea, Pacific purple and Mediterranean purple urchins are marked not reef safe because they cannot live in a tropical reef tank. Beyond the marks, every invertebrate is drip acclimated, because a salinity swing kills it, and no copper ever touches the tank.

01
Reef safe
Does not eat coral as a habit, but hermits can kill snails for shells
02
Caution
Usually fine, with a known habit on the profile
03
Drip acclimate
A salinity swing kills an invertebrate
04
No copper
Fish medications wipe out every animal here

The crew

The clean-up crew

The peppermint shrimp is marked beginner at 2 inches (5 cm) and eats Aiptasia. The cerith snail works the sand and glass, the nassarius snail lives in the sand and eats leftovers, both marked beginner for 11 gallons (40 liters). The emerald crab eats bubble algae at 2.4 inches (6 cm) and is marked caution. A hungry one can turn on small fish, snails, hermits and shrimp. The scarlet reef hermit crab reaches 1.6 inches (4 cm) and is one of four hermits marked peaceful. The Mexican turbo snail is the heavy grazer at 2.4 inches (6 cm), marked easy. The clean-up crew list covers the rest.

Echinoderms

Urchins, stars and cucumbers

The long-spine urchin reaches 9.8 inches (25 cm) across and lists 50 gallons (190 liters), a grazer marked easy with spines that go through a glove. The purple urchin is the smaller grazer at 3.1 inches (8 cm) for 20 gallons (75 liters). The sand-sifting star cleans the sand bed at 4.7 inches (12 cm) and lists 53 gallons (200 liters), because a smaller bed runs out of food. The serpent star scavenges under the rock at 11.8 inches (30 cm) across, marked easy. The sand-sifting sea cucumber turns the sand at 7.1 inches (18 cm) for 20 gallons (75 liters). The chocolate chip star is marked not reef safe, because it eats coral.

Anemones and clams

Rock flowers, carpets and giant clams

The rock flower anemone stays where it is put at 3.9 inches (10 cm) for 20 gallons (75 liters), marked medium. The maxi-mini carpet anemone is smaller at 3.1 inches (8 cm), with the same tank size and rating. The long tentacle anemone reaches 15.7 inches (40 cm) and hosts Clark's and pink skunk clownfish. The maxima clam is the giant clam with the colors, marked medium for 40 gallons (150 liters) on the rock under strong light. The crocea clam is the smallest at 5.9 inches (15 cm) and marked difficult for the light it needs. The squamosa clam sits on the sand at 15.7 inches (40 cm), marked medium.

Specialists

Showpieces and specialists

The harlequin shrimp is 2 inches (5 cm) of blue and white that eats only starfish, marked medium for that reason. The Berghia nudibranch is 0.8 inches (2 cm), eats only Aiptasia and starves when the Aiptasia is gone. The lettuce sea slug grazes hair algae at 1.6 inches (4 cm) for 11 gallons (40 liters). The giant feather duster filters the water with a 5.9 inch (15 cm) crown, marked medium. The sea apple is 7.1 inches (18 cm) of color, marked difficult, and it releases a toxin when it dies that can take the tank with it. The pom-pom crab carries a small anemone in each claw and reaches about 1 inch (2.5 cm).

By the numbers

Smallest

Largest

Easiest to keep

Most peaceful

Fits a 20 gallon tank

Fits a 30 gallon tank

FAQ

Common questions

Which marine invertebrates are easiest?

The skunk cleaner and peppermint shrimp, the trochus, cerith and nassarius snails and the blue-leg hermit crab are among the sixteen marked beginner. The tuxedo urchin and the serpent star are marked easy.

Are starfish reef safe?

The sand-sifting star, Fromia star, blue linckia star and multicolor sea star are marked reef safe. The serpent and brittle stars carry a caution, and the green brittle star catches sleeping fish. The chocolate chip and red knob stars are marked not reef safe because they eat coral.

Why did my invertebrate die after I added it?

Acclimation, most often. A snail, shrimp or starfish dropped into water of a different salinity dies within days. Drip acclimate over an hour, and check that no copper medication has ever been used in the tank.

What eats Aiptasia?

The peppermint shrimp, marked beginner, and the Berghia nudibranch, which eats nothing else and starves once the Aiptasia is gone. The Spurilla nudibranch clears an outbreak faster, but it also eats ornamental anemones. The copperband butterflyfish, the Aiptasia eating filefish and the Molly Miller blenny eat it too, though not every fish takes to it.

Can I keep an anemone with a clam?

Yes, with room between them. An anemone stings whatever it touches and walks until it settles, so the clam sits well outside its reach.

Do sea urchins eat coral?

Some do. Most urchins graze algae and coralline off the rock, but the Caribbean long-spined urchin and the banded urchin also eat coral tissue. The fire urchin is marked not reef safe and does not belong with other invertebrates. The caution mark on most urchins is for what they knock over and carry: a tuxedo urchin will walk off with a frag on its back.