Reef Hitchhiker Identifier: Bristle Worms, Aiptasia & Pests

A thin, segmented scavenger that eats leftover food, detritus and dead animals. Almost every reef tank has them.

10–150 mm (0.39–5.9 in) · Night (lights off)

A large, thick predatory bristle worm that eats coral tissue, anemones, clams and snails.

75–300 mm (3–11.8 in) · Day and night

A long, smooth predatory worm that lives deep in live rock and can eat snails, shrimp, small fish and coral.

100–1000 mm (3.9–39.4 in) · Night (lights off)

A hidden worm that spreads long, sticky, spaghetti-like feeding tentacles over the sand to pick up detritus.

50–300 mm (2–11.8 in) · Day and night

A filter-feeding worm living in a soft, papery tube that opens a feathery crown to catch plankton.

5–100 mm (0.2–3.9 in) · Day and night

A colourful filter-feeding worm that lives in a hard tube, usually inside a Porites rock or coral.

5–40 mm (0.2–1.6 in) · Day and night

Tiny filter-feeding worms that build hard, flat white coils on the glass, pumps and rock.

1–4 mm (<0.1–0.16 in) · Day and night

A fast-spreading pest anemone that stings nearby corals and multiplies from tiny fragments of itself.

5–50 mm (0.2–2 in) · Day and night

A small pest anemone that spreads across rock by splitting and stings neighbouring corals.

5–40 mm (0.2–1.6 in) · Day and night

Tiny stinging polyps that grow in fuzzy patches or feather shapes from a creeping network and can sting and kill corals they touch.

1–20 mm (<0.1–0.79 in) · Day and night

Tiny rust-red flatworms that bask in the light and multiply fast; plagues smother corals and release toxins when they die.

2–6 mm (<0.1–0.24 in) · Daytime

A camouflaged flatworm that eats Acropora tissue and can wipe out an SPS collection.

2–12 mm (<0.1–0.47 in) · Day and night

Tiny sea slugs that hide under plating Montipora and eat the tissue, leaving bare white patches.

2–10 mm (<0.1–0.39 in) · Day and night

Camouflaged sea slugs that eat zoanthids and Palythoa polyps from the base of the colony.

3–25 mm (0.12–0.98 in) · Night (lights off)

Small stubby-armed starfish that graze film algae and detritus. Most are harmless, but some populations nibble corals.

3–15 mm (0.12–0.59 in) · Day and night

A small scavenging star with a round disc and long, thin arms that cleans detritus from rock and sand.

5–60 mm (0.2–2.4 in) · Night (lights off)

A snail cemented in a hard tube that casts sticky mucus nets to catch food; the mucus irritates SPS and LPS corals.

3–50 mm (0.12–2 in) · Day and night

Tiny parasitic snails that feed on Tridacna clams (and some other snails) at night and can kill a clam.

1–5 mm (<0.1–0.2 in) · Night (lights off)

A fast, flat snail with a small ear-shaped shell that grazes film algae and breeds well in reef tanks.

5–30 mm (0.2–1.2 in) · Night (lights off)

Tiny round snails that graze film algae and diatoms and often breed in large numbers.

2–6 mm (<0.1–0.24 in) · Day and night

A flat-coiled snail that eats zoanthid and Palythoa polyps, usually from under the colony.

3–20 mm (0.12–0.79 in) · Night (lights off)

A flat grazing mollusc with eight shell plates that scrapes film algae off rock and glass.

5–40 mm (0.2–1.6 in) · Night (lights off)

A hairy, heavy-clawed crab that hides in rock by day and eats snails, small fish, coral polyps and zoanthids at night.

10–50 mm (0.39–2 in) · Night (lights off)

Small, stocky rock crabs, often with black-tipped claws. Small ones are usually harmless scavengers; larger ones can attack snails and corals.

5–40 mm (0.2–1.6 in) · Night (lights off)

A green herbivorous crab that eats bubble algae and film algae; large adults can turn opportunistic.

10–50 mm (0.39–2 in) · Day and night

A small crab that lives in branching Pocillopora, Stylophora and Seriatopora and defends its coral from predators.

8–25 mm (0.31–0.98 in) · Day and night

A predatory crustacean that lives in rock burrows and kills snails, crabs, shrimp and small fish. Often heard clicking at night.

25–150 mm (0.98–5.9 in) · Day and night

A small burrowing shrimp with one oversized snapping claw. Loud, but rarely harmful in a reef.

15–50 mm (0.59–2 in) · Night (lights off)

Tiny crustaceans that eat algae and detritus and are a key live food for mandarins, wrasses and corals.

0.5–2 mm (<0.1–<0.1 in) · Night (lights off)

Small shrimp-like scavengers that eat detritus and algae and feed many fish.

2–15 mm (<0.1–0.59 in) · Night (lights off)

A fast-swimming scavenger isopod that bites resting fish at night, causing wounds and sometimes death.

3–20 mm (0.12–0.79 in) · Night (lights off)

Tiny parasitic copepods that live on Acropora and make it lose colour and polyp extension.

0.5–1 mm (<0.1–<0.1 in) · Day and night

Thin-legged marine arthropods that suck the tissue out of zoanthid and other coral polyps.

2–10 mm (<0.1–0.39 in) · Night (lights off)

Filter-feeding animals that grow in shaded spots, overflows and sumps and help clean the water.

2–100 mm (<0.1–3.9 in) · Day and night

Filter feeders shaped like small jelly sacs with two openings, single or in colonies.

2–50 mm (<0.1–2 in) · Day and night