Illustrative orange fireworm with white bristles on purple live rock

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Sponges & Tunicates — Hitchhiker IDs

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 FragsLast reviewed:

Sponges & Tunicates

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Sycon ciliatum from temperate water: attached filter-feeder reference.

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.
Research sources
Clavelina robusta: attached filter-feeder reference.

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.
Research sources
Close-up of coral tentacles in purple, pink, blue and green

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