From RTAW Reefpedia

System startup is an exciting time, not only is it the start of a project, its the time when the first organisms are put in the tank as live rock. Rock harvested from a reef is covered in things not normally seen in the wild as we dont usually get sufficiently close to see them, being as tiny as they are. Below is a list of some of the numerous creatures, both good and bad, that may be introduced to a marine aquarium indirectly on / in live rock, corals, fish, water added to the system.

This page is organised into two sections, based on where the unidentified critter / item was discovered. Then each section is sub-divided into how or if it moved, then what its rough appearence is like. Each item then has an image, link to further information, quick notes on what it is, then a rough indication on whether it is something that is "good", "bad" or "depends".

If it still isn't possible to identify what it is, then post a photograph or detailed description (image is preferrable) on RTAW Forums.

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Contents 1 On A Surface 1.1 Stationary 1.1.1 Smooth 1.1.2 Spherical 1.1.3 Irregular 1.1.4 Tentacles, Arms 1.1.5 Hairy 1.1.6 Holes 1.2 Glides / Slides 1.3 Crawls / Walks 2 In The Water Column 2.1 Swims 2.2 Wiggles 2.3 Floats 2.4 Released 3 Resources

On A Surface

Things that may be found on a surface within the marine aquarium (fixed or moving) such as the sides of the tank, on the sand bed, on the liverock, on pumps etc.

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Stationary

Does not appear to actively move across the surface, remaining in the one location.

Smooth

Smooth in appearence, with no visible, distinct surface features.

Acoel Flatworm
Image:	Classification:	Comments:	Status:
	Acoel Flatworm	The acoel flatworm is a photosynthetic flatworm that can reach plague proportions. This is the main reason why they are undesirable, reaching plague proportions and smoothering sensile organisms such as corals. Another problem is that when they die, they release toxins into the water, which can make removing / killing them via chemical methods problematic. Some fish have a reputation for eating them, but it can vary between individuals whether they do or not. They tend to move slowly, but can move a significant distance in a hour or so. By observing closely, can see them glide over the surface and wriggle from side to side.

Chiton
Image:	Classification:	Comments:	Status:
	Cryptoplax sp.	Chitons are a type of mollusc that is found on liverock. They have eight protective hard plates that provide good protection from predators, with this particular genus the plates are reduced and mostly hidden. They feed on algae, bryozoans, diatoms and sometimes bacteria.

Chiton
Image:	Classification:	Comments:	Status:
	Polyplacophora	Chitons are a type of mollusc that is found on liverock. They have eight protective hard plates that provide good protection from predators. They feed on algae, bryozoans, diatoms and sometimes bacteria.

Coralline Algae
Image:	Classification:	Comments:	Status:
	Corallinaceae	Coralline algae is the purple / pink coverage on rocks that many hobbyists find highly desirable. It comes in a variety of shades, varying from white to deep red/purple. It is a calcareous algae with typically a "plated" growth form, gradually encrusting over the surface on which it grows. There are also some common species that are branched. It does not provide any real direct benefit other than looking visually appealing. However, is a good indicator of water conditions that are conducive for good hard coral growth. To grow well, coralline algae requires sufficient calcium and alkalinity levels. It can be eaten by various types of sea urchins.

Diatoms
Image:	Classification:	Comments:	Status:
	Bacillariophyceae	Brown to gold coating on sand bed, liverock and glass during the cycling process is due to diatoms which are going through a bloom. All part of a normal cycle process of a newly set up aquarium.

Liverock Die Off
Image:	Classification:	Comments:	Status:
	Liverock / Cycling	White areas on new liverock that is going through the cycling process appear that can look like "cobwebs" or "fungus". This is due to benthic organisms, such as sponges, corals or ascidians, dying. The death is likely to be due to the stress during the shipping of the liverock (which the hobbyist has no control over) or due to the high levels of ammonia / nitrite during the cycling process (which the hobbyist has control over).

Slime Algae
Image:	Classification:	Comments:	Status:
	Cyanobacteria	Cyanobacteria is also called 'slime algae due to being very slimy to touch. It is present within any healthy marine aquarium system but can become a problem when it reaches bloom proportions, coating the sand bed, liverock and even corals. New systems go tend to go through a stage when the cyanobacteria blooms, but that typically disappears after a couple of weeks. Sustained issues with cyanobacteria tends to indicate elevated nutrient levels that need to be addressed.

Slime Algae
Image:	Classification:	Comments:	Status:
	Cyanobacteria	Cyanobacteria is also called 'slime algae due to being very slimy to touch. The bubbles trapped under the cyanobacteria is oxygen bubbles generated by photosynthesis and will be most visible towards the end of the photoperiod. It is present within any healthy marine aquarium system but can become a problem when it reaches bloom proportions, coating the sand bed, liverock and even corals. New systems go tend to go through a stage when the cyanobacteria blooms, but that typically disappears after a couple of weeks. Sustained issues with cyanobacteria tends to indicate elevated nutrient levels that need to be addressed.

Flatworm
Image:	Classification:	Comments:	Status:
	Flatworm	Quick details about the organism.

Snail Eggs
Image:	Classification:	Comments:	Status:
	Turbo sp.	Turbo snails lay their eggs in a gelatinous mass with the eggs visible as small dots. These snails have a good record in captivity of the eggs being able to produce larvae that survive sufficiently to produce baby snails.

Spherical

Shaped roughly like a ball with a smooth surface.

Clownfish Eggs
Image:	Classification:	Comments:	Status:
	Anemonefish	Quick details about the organism.

Cirolanid Isopod
Image:	Classification:	Comments:	Status:
	Isopoda	Considered a parasite, but probably a better name for a cirolanid isopod is predator that is simply too small to actually consume their prey entirely. Typically found attached to the side of a fish, but can easily detach and swim around the tank. Relatively rarely found in marine aquaria.

Foraminiferan
Image:	Classification:	Comments:	Status:
	Foraminifera	These types of small, snail shell shaped, slowly mobile foraminiferans are typically noticed just above the sand bed surface attached to the glass. They do not cause any problems and are sign of a healthy system.

Sundial Snail
Image:	Classification:	Comments:	Status:
	Heliacus sp.	These snails are exclusive predators of zoanthids, which may or may not be a good thing.

Bubble Algae
Image:	Classification:	Comments:	Status:
	Valonia	Bubble Algae is typically found on newly added liverock or even on the rock that corals are purchased on. Can be problematic in a marine aquarium and it can encroach over desirable corals, causing them to recede and eventually to die.

Irregular

Highly irregular shape, overall or with protusions from the body.

Barnacles
Image:	Classification:	Comments:	Status:
	Cirripedia	Barnacles are a type of crustacean that lives fixed to a surface and collects food from the passing water. They can be found living within some hard coral colonies, such as Porites sp., Favia sp. and Galaxea sp., taking up residence between the coral polyps. They do not cause any problems for the coral at all, simply living between the polyps collecting food particles as they float past.

Bristle Cage Worm
Image:	Classification:	Comments:	Status:
	Flabelligeridae	Typically seen living in liverock, with their fine, long setae (look like glass fibres) protuding from the surface in a conical, fanned shape arrangement. They are filter feeders.

Fan Worm
Image:	Classification:	Comments:	Status:
	Serpulidae	Quick details about the organism.

Foraminiferan
Image:	Classification:	Comments:	Status:
	Foraminifera	These types of fixed, branching foraminiferans are typically found growing on the underside and dark areas of liverock. They do not cause any problems and are sign of a healthy system.

Foraminiferan
Image:	Classification:	Comments:	Status:
	Foraminifera	These types of fixed, branching foraminiferans are typically found growing on the underside and dark areas of liverock. They do not cause any problems and are sign of a healthy system.

Halimeda
Image:	Classification:	Comments:	Status:
	Halimeda sp.	Calcerous algae which requires good calcium and alkalinity levels to grow well. Can go sexual, with means that it forms sexual organs (gametangia) and losses pigmentation, appearing predominately white with small green spots. After completion of the act, the original plant dies it is totally white.

Nudibranch
Image:	Classification:	Comments:	Status:
	Tritoniopsis elegans	This nudibranch feeds on soft corals such as Sinularia and Lobophytum sp.. Can be very difficult to spot on the coral and may cause the polyps to be retracted in the area it is located.

Scale Worm
Image:	Classification:	Comments:	Status:
	Polynoidea	Slow moving predators that feed on things like small crustaceans, echinoderms, polychaetes, gastropods, sponges and hydroids. A significant number live symbiotically with asteroids, echinoids, holothorians, sea anemones, sea grasses and corals.

Spindle Weed
Image:	Classification:	Comments:	Status:
	Neomeris sp.	Calcerous algae which requires good calcium and alkalinity levels to grow well. Tends to appear on fresh liverock but rarely survives long term.

Sponge
Image:	Classification:	Comments:	Status:
	Porifera	Quick details about the organism.

Vermetid Snail
Image:	Classification:	Comments:	Status:
	Vermetidae	This group of snails have forgone their mobility by attaching their "shell" to the substrate and converting it into a calcerous tube. They release a mucus web out into the water, which they then reel back in and consume, eating the food particles caught in it. Their presence is a sign of a healthy system and don't typically cause any problems. The exception is if the mucus net irritates a neighbouring coral, which can lead to death of the polyps that it is irritating.

Tentacles, Arms

Tentacle(s), arm(s) or some other appendage(s) are visible, moving around either within the water or along the surface while the base or the organism is anchored on a surface.

Anemonea
Image:	Classification:	Comments:	Status:
	Anemonia sp.	This is a pest anemone, which can multiply quickly, have a strong sting, and can potentially over take a tank with easy. Not as prolific as Aiptasia sp., but are more difficult to kill. Manual removal from the rock or killing the anemones using injections of kalkwasser / vinegar / hydrochloric acid / caustic soda as soon as they are discovered is recommended.

Brittle Star
Image:	Classification:	Comments:	Status:
	Ophiuroidea	Commonly referred to as Brittle Stars, vast majority of species are good scavengers to have. Smaller species will reproduce.

Brittle Star
Image:	Classification:	Comments:	Status:
	Ophiuroidea	Commonly referred to as Brittle Stars, vast majority of species are good scavengers to have. Smaller species will reproduce.

Brown Hydroid
Image:	Classification:	Comments:	Status:
	Myrionema sp.	This colonial hydroid can grow very quickly and has a powerful sting. For this reason it is typically thought of as a pest. It prefers high light and high water movement areas and can be difficult to remove from rocks when it starts to spread. Moving the rock to a low light area can be successful, with it then quickly dying off.

Bryozoan
Image:	Classification:	Comments:	Status:
	Bryozoa	Look similar to corals in that they form colonies and have many polyps over the surface, however that similarity is only superficial.

Comb Jelly
Image:	Classification:	Comments:	Status:
	Ctenophora	The type typically seen in captivity are observed when they are feeding, with two long tentacles let out into the current. They are regularly fully retracted into the body to consume the food particles collected. The tentacles have a combed shape, with closely spaced shorter tentacles joined to the main, long tentacles. The animals main body can be difficult to observe on the liverock surface as they tend to be small and well camouflaged.

Feather Star
Image:	Classification:	Comments:	Status:
	Crinoidea	Commonly referred to as Feather Stars and may be a hitchhiker on liverock. Typically don't do well in captivity due to lack of prey in the water column, they are suspension feeders.

Glass Anemone
Image:	Classification:	Comments:	Status:
	Aiptasia sp.	More correctly referred to as Aiptasia, these are definitely a pest anemone. They multiple very quickly, have a very nasty sting that can cause significant injury to other tank mates (both corals and fish) and can potentially over take a tank with ease. Removal methods include introduction of the predators Lysmata vittata (Peppermint Shrimp) or Chelmon rostratus (Copper Banded Butterfly), or killing the anemones using injections of boiling water / kalkwasser / vinegar / hydrochloric acid / caustic soda / Joes Juice (commercial product). Remove from a system as promptly as possible.

Hydroid
Image:	Classification:	Comments:	Status:
	Hydrozoa	Quick details about the organism.

Medusa Worm
Image:	Classification:	Comments:	Status:
	Synaptidae	Detritus feeder.

Peanut Worm
Image:	Classification:	Comments:	Status:
	Sipuncula	Worm that lives within the liverock or substrate, with only their introvert seen protruding from the burrow for feeding on detritus. Part of a healthy marine aquarium system.

Sea Cucumber
Image:	Classification:	Comments:	Status:
	Holothuria	Sea cucumbers are common hitchhikers on liverock, with the suspension feeders like this one more typical. The tentacles are for capturing plankton from the water column.

Spaghetti Worm
Image:	Classification:	Comments:	Status:
	Terebellidae	Quick details about the organism.

Spionidae Worm
Image:	Classification:	Comments:	Status:
	Spionidae	Quick details about the organism.

Vermetid Snail
Image:	Classification:	Comments:	Status:
	Vermetidae	This group of snails have forgone their mobility by attaching their "shell" to the substrate and converting it into a calcerous tube. They release a mucus web out into the water, which they then reel back in and consume, eating the food particles caught in it. Their presence is a sign of a healthy system and don't typically cause any problems. The exception is if the mucus net irritates a neighbouring coral, which can lead to death of the polyps that it is irritating.

Waratah Anemone
Image:	Classification:	Comments:	Status:
	Actinia tenebrosa	Temperate species, so unlikely to do well in most tropical reef systems.

Hairy

It appears to be hairy or furry in appearance, with a large number of appendages or strands.

Bristle Cage Worm
Image:	Classification:	Comments:	Status:
	Flabelligeridae	Typically seen living in liverock, with their fine, long setae (look like glass fibres) protuding from the surface in a conical, fanned shape arrangement. They are filter feeders.

Bryopsis
Image:	Classification:	Comments:	Status:
	Bryopsis	Problematic algae that can be difficult to remove once it gets a footing in an aquarium.

Brown Hydroid
Image:	Classification:	Comments:	Status:
	Myrionema sp.	This colonial hydroid can grow very quickly and has a powerful sting. For this reason it is typically thought of as a pest. It prefers high light and high water movement areas and can be difficult to remove from rocks when it starts to spread. Moving the rock to a low light area can be successful, with it then quickly dying off.

Christmas Tree Worm
Image:	Classification:	Comments:	Status:
	Spirobranchus	Typically seen living in the middle of Porites spp. colonies, which they have a symbiotic relationship with. Will rapidly retract into the rock when a shadow or movement is sensed. They are filter feeders.

Turtle Weed
Image:	Classification:	Comments:	Status:
	Chlorodesmis sp.	quick details about the organism

Holes

Surface has holes in it, may be many or few.

Ascidian
Image:	Classification:	Comments:	Status:
	Ascidiacea	Also know as tunicates. Can exist as solitary organisms which have two holes in their surface, as pictured to the left, or as a colony which is a number of individuals all side by side.

Ascidian
Image:	Classification:	Comments:	Status:
	Ascidiacea	Also know as tunicates. Can exist as solitary organisms which have two holes in their surface or as a colony which is a number of individuals all side by side, as pictured to the left.

Sponge
Image:	Classification:	Comments:	Status:
	Porifera	Very common on liverock and will tend to be more obvious on the undersides / out of direct light. The number of type of species found is huge, with many different colours and growth forms. Typically look like a coating over the rock with small holes of various sizes visible. Are filter feeders and their present and growth indicates a healthy system.

Sponge
Image:	Classification:	Comments:	Status:
	Porifera	Very common on liverock and will tend to be more obvious on the undersides / out of direct light. The number of type of species found is huge, with many different colours and growth forms. Typically look like a coating over the rock with small holes of various sizes visible. Are filter feeders and their present and growth indicates a healthy system.

Sponge
Image:	Classification:	Comments:	Status:
	Porifera	Very common on liverock and will tend to be more obvious on the undersides / out of direct light. The number of type of species found is huge, with many different colours and growth forms. Typically look like a coating over the rock with small holes of various sizes visible. Are filter feeders and their present and growth indicates a healthy system.

Vermetid Snail
Image:	Classification:	Comments:	Status:
	Vermetidae	This group of snails have forgone their mobility by attaching their "shell" to the substrate and converting it into a calcerous tube. They release a mucus web out into the water, which they then reel back in and consume, eating the food particles caught in it. Their presence is a sign of a healthy system and don't typically cause any problems. The exception is if the mucus net irritates a neighbouring coral, which can lead to death of the polyps that it is irritating.

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Glides / Slides

Actively moves across the surface, but difficult to see the manner in which it moves, appearing to glide over the surface.

Abalone
Image:	Classification:	Comments:	Status:
	Haliotis sp.	Quick details about the organism.

Acoel Flatworm
Image:	Classification:	Comments:	Status:
	Acoel Flatworm	The acoel flatworm a photosynthetic flatworm that can reach plague proportions. This is the main reason why they are undesirable, reaching plague proportions and smoothering sensile organisms such as hard corals. Another problem is that when they die, they release toxins into the water, which can make removing / killing them via chemical methods problematic. Some fish have a reputation for eating them, but it can vary between individuals. They tend to move slowly, but can move a significant distance in a hour or so. By observing closely, can see them glide over the surface and wriggle from side to side.

Black Limpet
Image:	Classification:	Comments:	Status:
	Scutus unguis	Algae eater.

Black Nudibranch
Image:	Classification:	Comments:	Status:
	Dendrodoris nigra	Quick details about the organism.

Bristle Worm
Image:	Classification:	Comments:	Status:
	Amphinomidae	Majority of bristle worms found in a marine aquarium are beneficial scavengers and crucial members of the live sand community. They are active scavengers and predators, but most are strictly opportunistic feeders, simply eating what they can capture.

Bristle Worm
Image:	Classification:	Comments:	Status:
	Amphinomidae	Majority of bristle worms found in a marine aquarium are beneficial scavengers and crucial members of the live sand community. They are active scavengers and predators, but most are strictly opportunistic feeders, simply eating what they can capture.

Chiton
Image:	Classification:	Comments:	Status:
	Polyplacophora	Chitons are a type of mollusc that is found on liverock. They have eight protective hard plates that provide good protection from predators. They feed on algae, bryozoans, diatoms and sometimes bacteria.

Eunice Worm
Image:	Classification:	Comments:	Status:
	Eunice sp.	Type of worm that is characterised by having five tentacles. They are predators, with some species eating soft corals and zoanthids. Small species should not cause any serious problems, but worth keeping an eye on their behaviour to see what they are eating.

Flatworm
Image:	Classification:	Comments:	Status:
	Flatworm	Quick details about the organism.

Nudibranch
Image:	Classification:	Comments:	Status:
	Tritoniopsis elegans	This nudibranch feeds on soft corals such as Sinularia and Lobophytum sp.. Can be very difficult to spot on the coral and may cause the polyps to be retracted in the area it is located.

Limpet
Image:	Classification:	Comments:	Status:
	Patellogastropoda	Quick details about the organism.

Medusa Worm
Image:	Classification:	Comments:	Status:
	Synaptidae	Detritus feeder.

Predatory Whelk
Image:	Classification:	Comments:	Status:
	Cronia avellana	Prey includes: echinoderms, peanut worms, polychaetes, crustaceans, chitons, gastropods, barnacles and bivalves.

Ribbon Worm
Image:	Classification:	Comments:	Status:
	Nemertea	Quick details about the organism.

Sea Cucumber
Image:	Classification:	Comments:	Status:
	Holothuroidea	Sea cucumbers are common hitchhikers on liverock, with the suspension feeders like this one more typical. The tentacles are for capturing plankton from the water column.

Stomatellid
Image:	Classification:	Comments:	Status:
	Stomatella sp.	Quick details about the organism.

Turbo Snail
Image:	Classification:	Comments:	Status:
	Turbo sp.	Quick details about the organism.

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Crawls / Walks

Actively moves across the surface and the appendages that allow the motion are clearly visible.

Amphipod
Image:	Classification:	Comments:	Status:
	Amphipoda	Quick details about the organism.

Brittle Star
Image:	Classification:	Comments:	Status:
	Ophiuroidea	Quick details about the organism.

Cirolanid Isopod
Image:	Classification:	Comments:	Status:
	Isopoda	Considered a parasite, but probably a better name for a cirolanid isopod is predator that is simply too small to actually consume their prey entirely. Typically found attached to the side of a fish, but can easily detach and swim around the tank. Relatively rarely found in marine aquaria.

Copepod
Image:	Classification:	Comments:	Status:
	Copepoda	quick details about the organism

Green Decorator Crab
Image:	Classification:	Comments:	Status:
	Huenia sp.	quick details about the organism

Mantis Shrimp
Image:	Classification:	Comments:	Status:
	Stomatopoda	Mantis shrimp are regarded by many hobbyists as pests, but with the exception of a few species, mainly the spearers, many can live for many years in a aquarium with other organisms and cause no noticeable damage, other than taking a few snails from time to time. Large spearers can be quite beautiful and make great subjects for a dedicated tank.

Sea Spider
Image:	Classification:	Comments:	Status:
	Pantopoda	The sea spiders tend to be discovered after a recent addition of new liverock. The common ones seen can range in size from 1 to 10 mm. They do not cause any problems, due to their very small size.

Pistol Shrimp
Image:	Classification:	Comments:	Status:
	Alpheus	quick details about the organism

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In The Water Column

Things that may be spotted moving through the water of the marine aquarium, either actively moving or floating with the current.

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Swims

Actively moves through the water, using some appendages to "swim", whether that is via arms, tentacles, or fins.

Cirolanid Isopod
Image:	Classification:	Comments:	Status:
	Isopoda	Considered a parasite, but probably a better name for a cirolanid isopod is predator that is simply too small to actually consume their prey entirely. Typically found attached to the side of a fish, but can easily detach and swim around the tank. Relatively rarely found in marine aquaria.

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Wiggles

Actively moves through the water, using its own body to move, in a snake-like manner.

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Floats

Doesn't actively move through the water, but simply floats with the current where ever that goes.

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Released

Things that are released into the water column from a surface.

Snail Spawning
Image:	Classification:	Comments:	Status:
	Turbo sp.	White cloud or smoke released by a snail from a raised location on the reef structure, is sperm.

Starfish Spawning
Image:	Classification:	Comments:	Status:
	Asteroidea	White cloud or smoke released by the starfish, which arches it's body in raised location on the reef structure, is sperm.

Urchin Spawning
Image:	Classification:	Comments:	Status:
	Echinoidea	White "spaghetti" released from the center / top of the urchin, typically on a raised location the reef structure around dusk. The spaghetti then breaks up in the water column into smaller particles.

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Resources

• Hitchhiker FAQ - Reefs.org
• Hitchhiker FAQ - Xtalreef