Found something in your reef? Compare the shape, movement and distinctive features below to identify the hitchhiker and decide what to do.
Friend: usually useful or harmless. Caution: identification or behaviour changes the risk. Pest: confirm the organism before managing it. Photographs show reference examples; similar-looking animals may be different species.
Written by Christian, Signature Frags · Last reviewed:
Search by common name, scientific name or abbreviation.
A ball-tipped corallimorph identified at source as Corynactis globulifera (formerly Pseudocorynactis globulifera). The photograph is a reference example.
Small examples can be tolerated; larger predatory forms need care.
Quick ID
A small disc surrounded by translucent tentacles with conspicuous rounded tips, often pale or orange. The tentacle tips give the “ball” appearance.
Typical size
Many aquarium finds are centimetre scale. Related ball-tipped corallimorphs can grow much larger; do not assume all stay tiny.
Usually found
Shaded holes, rock undersides and areas where suspended food passes.
Commonly confused with
Aiptasia, small true anemones and mushroom corals. A rounded tentacle tip is useful, but not sufficient for an exact genus identification.
Worth knowing
These are corallimorphs, not true anemones. The hobby name covers more than one taxon; feeding risk cannot be inferred confidently from the name alone.
What should I do?
Observe growth and neighbouring livestock. Move sensitive frags away from contact. Isolate a large or actively troublesome specimen rather than assuming every small one needs eradication.
Corynactis californica at Steinhart Aquarium: a temperate strawberry-anemone reference, not a tropical husbandry example.
Strawberry anemones
Caution
Corynactis spp.; common-name identification guide
Common names overlap; temperate Corynactis are not suitable additions to a warm reef.
Quick ID
Small, brightly coloured corallimorphs with conspicuous rounded tentacle tips; some form close groups of red, pink or orange individuals.
Typical size
Typically small: C. californica is approximately 2.5 cm wide; dimensions vary by species and whether the tentacles are extended.
Usually found
C. californica inhabits temperate Pacific rocky reefs; C. viridis is a temperate Atlantic jewel anemone. Tropical look-alikes also arrive on live rock.
Commonly confused with
Ball anemones, small mushrooms and true anemones. Strawberry is a common name, not a reliable species or temperature requirement.
Worth knowing
These are corallimorphs rather than true anemones. Do not buy or introduce a temperate strawberry/jewel anemone for a tropical reef based on this photograph.
What should I do?
Photograph and establish origin before treating or keeping it. Check the separate ball-anemone card for tropical finds. Protect neighbouring coral from contact and identify any growing colony.
Sycon ciliatum from temperate water: a vase-shaped sponge morphology reference, not a confirmed tropical aquarium species.
Pineapple sponges
Friend
Calcarea; Sycon-type sponges
Generally harmless filter feeders when not covering coral.
Quick ID
A small pale tube or vase attached to a surface, often rough or fuzzy, with a single opening surrounded by a fringe at the top.
Typical size
Commonly noticed at millimetre to small-centimetre scale. Sycon ciliatum can reach about 5 cm; that is not an aquarium-species diagnosis.
Usually found
Shaded rock, sump walls, overhangs, plumbing and beneath frag plugs.
Commonly confused with
Closed tunicates, egg capsules and tiny tube worms. A sponge has pores and an outflow opening, rather than a retracting feather crown.
Worth knowing
“Pineapple sponge” is an aquarium appearance label, not a confirmed species. These animals filter suspended material; their presence alone does not diagnose poor water quality.
What should I do?
Leave isolated growths. If a growth is physically covering living coral or obstructing equipment, remove only the affected patch during maintenance.
Clavelina robusta: a tropical colonial sea-squirt example showing the openings of individual zooids.
Tunicates / sea squirts
Friend
Ascidiacea; Tunicata
Usually harmless attached suspension feeders.
Quick ID
A soft or leathery attached sac with two siphons, or a colony of small sacs sharing an encrusting base. Siphons may close when disturbed.
Typical size
Individuals range from millimetres to several centimetres; colonial sheets can spread much farther.
Usually found
Shaded rock, undersides of frags, overhangs, shells and sump surfaces.
Commonly confused with
Sponges and closed polyps. Two distinct siphons are useful on solitary forms; colonial tunicates may be harder to recognise.
Worth knowing
Tunicates filter suspended particles and can struggle in very food-poor systems. The small hitchhikers and large decorative species sold deliberately do not necessarily have the same husbandry needs.
What should I do?
Leave healthy growth away from living coral. Remove a limited patch if it is overgrowing a valued organism or obstructing equipment. Do not dose extra food without considering the tank’s nutrient load.
Bugula neritina colony: one branching bryozoan form. Encrusting species can look very different.
Bryozoans
Friend
Bryozoa; colonial filter feeders
Usually harmless filter feeders; monitor colonies that spread onto living coral.
Quick ID
Fine branching lace, a small bush, or a regular encrusting patch made of repeated tiny units. Magnification may reveal tentacle crowns emerging from individual zooids.
Typical size
Individual zooids are tiny; colonies can spread from a small patch to several centimetres or more.
Usually found
Shaded rock, coral skeleton, shells, frag undersides and other firm surfaces.
Commonly confused with
Hydroids, sponges, tunicates and coralline crusts. A repeated regular zooid pattern and feeding crowns can help distinguish them.
Worth knowing
The branching Bugula photograph is one form. Encrusting bryozoans may resemble a pale lace-like crust and need a separate close look.
What should I do?
Usually leave in place. Monitor growth near living coral; gently manage troublesome colonies on removable surfaces without scraping the coral tissue.
Isognomon californicum: a living attached marine bivalve example, not a confirmed ID of a tiny reef clam.
Harmless bivalves / tiny clams
Friend
Bivalvia; small free-living or attached forms
For ordinary small hitchhiking bivalves identified away from sensitive tissue.
Quick ID
Two shell halves joined by a hinge, opening slightly to expose soft edges or siphons. Some attach with fine byssal threads; others sit in rock crevices.
Typical size
Often noticed at millimetre to small-centimetre scale. A tiny animal may be a juvenile of a larger species.
Usually found
Live rock, rubble, crevices, shell surfaces and occasionally within porous rock.
Commonly confused with
Brachiopods, closed tunicates and empty shells. A living bivalve has two hinged valves; shape alone may not establish the species.
Worth knowing
Most familiar small hitchhikers depend on suspended food. They should not be treated like deliberately purchased photosynthetic Tridacna clams; stronger lighting alone does not supply their food.
What should I do?
Leave healthy, unobtrusive individuals. Do not pull an attached clam free by force. Remove a dead, gaping animal if its tissue is decomposing and identify unusual growth affecting coral.
Nucella lapillus egg capsules: a temperate marine-snail example, not a claim that these are typical tropical reef-snail eggs.
Snail egg masses
Caution
Gastropoda; several possible parent species
Keep known grazer eggs; identify unfamiliar clutches before deciding.
Quick ID
Clusters of capsules, tiny dots within jelly, strings, loops or ribbons fixed to glass or rock. Egg shape depends heavily on the parent species.
Typical size
Individual eggs may be microscopic; capsules are often millimetre scale, while a complete ribbon or string can extend centimetres.
Usually found
Glass, pumps, frag plugs, rock and the undersides of sheltered surfaces.
Commonly confused with
Spirorbid tubes, hydroids, sponges and worm egg masses. Hard coiled tubes or feeding tentacles point away from an egg clutch.
Worth knowing
A clutch does not identify the parent on its own, and snail eggs are not automatically pest eggs. Whether larvae survive in a reef tank depends on the species’ development and food requirements.
What should I do?
Leave eggs observed being laid by a known suitable snail. Photograph and inspect unfamiliar masses; isolate a newly affected frag if a pest parent is suspected. Remove confirmed pest eggs carefully and monitor for further laying.
