Friend or Foe

Friend or FoeTRISTAN LOUGHER B.Sc. graduated from Manchester University in 1992 with a degree in Zoology. He has worked at Cheshire Waterlife for five years. Part 5 DIGITAL IMAGES BY THE AUTHOR

n the previous Friend or Foe article we Order : Mesogastropoda little harm to its host so an argument could began looking at the Molluscs that are Sub-order : Ptenoglossa be made for leaving it alone. After all, Ifrequently imported along with live Family : Thycidae many will never be spotted on seemingly rock and corals with particular attention Common name : None healthy starfish anyway! being given to the gastropods – i.e. slugs and snails. This article will continue that If you can spot this snail then you really do Sub-order : Ptenoglossa theme as there are so many different have excellent vision. The fascinating Family : Epitoniidae species worthy of a mention that 3000 Thyca crystallina lives as a parasite on Common name : Wentletraps words wasn’t enough! Finally, we will look starfish from the Genus Linckia ( Blue at the other molluscan group regularly starfish – see figure 22). Unfortunately, at the time of this article encountered in reef aquaria – the Bivalves. The snail actually looks like one half going to press I do not have any images of These include the popular clams and of a cockle shell and the fact that its this snail available. Wentletraps are scallops. brilliant blue colouration almost exactly potentially very serious predators of hard mirrors that of its host means it can be very corals in particular and may arrive in Order : Allogastropoda difficult to locate even when you are association with the corals upon which they Family : Architectonicidae looking for it! The animal feeds exclusively feed. There are several species in this Common name : Box snails or sundials. on the starfish so I have to recommend its family some of which are adapted to feed removal. However, long term observation exclusively on one coral species and their The chequered box snail (Heliacus sp.) is has noted that the animal seems to cause coloration and shell shape reflects this. one of the easiest molluscan pest species to spot and identify. The shell has a flattened Fig 22 Linckia sp. (Blue starfish) spire with obvious whorls. This shape, coupled with the fact that this snail is generally to be found snugly ensconced in the polyps that it is feeding on is a dead giveaway for this species. Figure 21 shows an individual removed from a colony of button polyps (Zoanthus sp.) . This specimen was around 7mm in diameter. There are other species of box and sundial snail that have the same basic shape as Heliacus sp.. They share its taste for invertebrates too; some feed on hard and soft corals. For this reason any snail with this shell shape should be removed from the aquarium.

Fig 21 Heliacus sp.

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waters. For an unknown reason, not thought Fig 23a Tubastrea sp. (Sun Coral) to be a natural population fluctuation, this snail has reached plague proportions and its predation is ultimately leading to large- scale die-off of much of the Ningaloo Reef, a popular diving resort where manta rays and whale sharks can be seen. Drupella snails reach about 5cm in length and adult specimens are usually covered in heavy growth of coralline algae making their clusters around the base of hard corals difficult to spot, indeed they are usually located by evidence of their feeding behaviour (white scars on the coral) rather than sightings of the animal itself. The Ningaloo reef situation reflects the potential problems an aquarist can experience when their aquarium is struck by a pest species with no natural controls on its population. Vigilance is the key!

Order : Neogastropoda Superfamily : Conacea Common name : Cone shells

Cone shells will be familiar to many people if only for the fact that they have beautiful conical shells often sold in the sea-shell Epitonium billeeanum is a wentletrap combs in some areas of the world. trade. However, this beauty hides the fact species that feeds exclusively on sun coral Muricacea have specialised radulae which that this family contains some of the most (Tubastrea coccinea) (Figure 23a). are capable of boring into shells.They do specialised predators in the gastropod Consequently, the shell and mantle of these this by secreting acids which break down assemblage. The radular teeth used by snails is bright orange making them the calcium carbonate thus giving access to limpets and turbo snails for scraping algae difficult to spot. Removal of every snail is the soft tissue beneath. This opens up all have evolved into very dangerous looking essential for the long-term health of the manner of feeding opportunities including harpoon-like teeth (Figure 26). coral species. clams and other bivalve molluscs, Many cone shells have a venom gland barnacles, corals and even other gastropods. attached to this tooth which is located at the Order : Neogastropoda One family, Chicoreus, is especially end of the highly manoeuvrable proboscis. Super-family : Muricacea dangerous as they predate the ornamental Upon locating prey the cone snail sneaks up Common names : Tridacnid clams and are a major problem in to the unsuspecting animal, usually a fish, Murex shells and rock shells culturing facilities. Fortunately, murex are and fires the harpoon into the flesh. The rare although I have found them in venom acts quickly but a fast swimming This grouping of snails includes some very association with Fijian live rock. They can fish in a state of shock can still move bad species indeed. Murex snails have be incredibly difficult to see as the many relatively great distances in a short time typically very ornate shells, some to a very projecting spines on the shell can become compared to a snail and so many species spectacular extent – they were even used as broken and encrusted with algae. Figure 23 remain attached to the “harpoon” and are shows a rock shell – another predatory muricid that was Fig 26 imported on a piece of soft coral. Some Muricid snails are wreaking havoc on the reefs of the world. Drupella cornus is a coral eating muricid from Western Australian Fig 23 Rock Snail

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dragged along with the dying prey. (Other hitch-hikers associated with live rock and may be present just waiting in your species prey on snails and do not “hold corals. They are basically a shell-less aquarium for the introduction of their food! onto” the harpoon once it has been gastropod resembling in basic body pattern Despite the beauty of these creatures discharged.) Once the fish is completely the slugs we find in our gardens. However the vast majority encountered are unwanted immobile the cone shell devours it. Some the degree of elaboration of this basic pests and should be removed from the cone shells have been known to take quite pattern is amazing and many species exhibit aquarium whenever a definite sighting is large fish this way. I have seen film of 8- incredible colouration. made. There are some techniques that can 10cm specimens consuming a lionfish The word Nudibranch literally be used to “drive” the slugs out of hiding which gives you some idea of the flexibility translates as “Naked gills” and most species which I will outline later but first, let’s have of this animal’s mouth and stomach. do indeed have very conspicuous gill a look at the rogues gallery. Most cone shells are harmless to filaments on the dorsal surface of the body. humans but some have venom so powerful Nudibranchs have evolved a variety of Order Nudibranchea it can kill humans. Fortunately it is defences to compensate for the lack of a Sub-order : Aeolidcea extremely unlikely that you will ever come shell. These include acid and toxin Family : Tergipedidae across one – I have found two in five secretions. Some species are able to Species : Phestilla lugubris years! If you suspect that a cone shell is assimilate the toxins and defence present in your aquarium then you should mechanisms of their prey into their tissues. Although first in the list I have only remove it with the utmost care, preferably Others that prey on hydroids and corals are ever encountered two individuals of able to relocate the immature nematocysts with forceps. this species but it is so incredibly well (stinging cells, such as those possessed by disguised that it is worthy of first Sub-class Heterobranchia anemones) of their prey into extensions of billing! This nudibranch feeds Order : Allogastropoda the mantle called cerata. Here they mature Family: Pyramidellidae and defend the slug against predators. exclusively on Porites hard coral. Elaboration of the cerata in several Many people will have small colonies The snails of concern to aquarists are small species has meant that they can mimic the of this coral as it is commonly to very small (less than 4mm) gastropods prey upon which they feed. Some species associated with live rock. However, the with a very high spire to the shell. As with of Aeolid nudibranch resemble star polyps. two instances that I have experienced many of the molluscs discussed in this The most troublesome family, the with them they have been located on Tritonidae are so well disguised that they article good eyesight and close scrutiny of “plume rock” where the Porites hard are difficult to notice even when you know specimen pieces is essential to spot these coral is surrounding multicoloured what you are looking for! little snails which prey on clams of the tubeworms ( Figure 25). genus Tridacna. The worst effected clams In certain species the cerata can be I was inspecting a piece of newly tend to be T.crocea, T.maxima and shed leaving a potential predator with some acquired Porites, noting the diversity of life T.squamosa due to the fact that they possess seemingly tasty morsels upon which to feed other than the tubeworms present when I projections of the shell called scutes where – but they get a nasty shock. One example spotted a slightly discoloured oval patch of the pyramid snails conceal themselves of this is a species that feeds on button polyps. I looked closer and saw that the during the day. At night they migrate to the polyps. “polyps” didn’t have the usual fine edge of the clam’s mantle and extend their Another potential problem with certain tentacles and wondered whether this was a proboscis and begin sucking the juices from species of nudibranch is the fact that they mutation or area of damage. Then it the tissue contained therein. Infestation have a larval stage that only begins its dawned on me – this was a very well with pyramid snails can be a reason for development when it comes into contact concealed nudibranch. Unfortunately, I no clams remaining closed or not expanding with the coral upon which it feeds. This longer have a specimen available to fully. Large numbers can see off the clam presents the possibility that larval stages photograph but it is essential to check every altogether. So what exactly are you looking for? Well, to the naked eye these gastropods look like small grains Fig 25 Porites sp. hard coral of rice lodged in and amongst the with associated tube worms scutes of the clam; only close examination with the naked eye, or preferably with a hand lens, reveals small whorls like a cerith snail in miniature. Before you introduce the clam it is always worth checking the scutes and also underneath at the base of the clam. To prevent any damage to the clam when removing them a cocktail stick is handy to prise them out or soft paintbrushes can work well for the more delicate areas.

Order : Nudibranchia Family Opistobranchia Common name: Sea slugs

Nudibranchs are amongst some of the most commonly encountered molluscan

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piece of Porites for this slug as it feeds on colour can vary from white to pink to pests. Be extremely careful when their polyps. Removal is best attempted by orange depending on the coral being attempting either of the techniques outlined prising the slug from the coral with a predated. The white form is a very common above. cocktail stick taking care not to damage import associated with Cladiella sp. soft healthy polyps. corals (Figure 28) . Even large ( 40mm) Miscellaneous specimens can remain undetected in an Order : Nudibranchia aquarium since they feed almost Nudibranchs Suborder: Dendrotonacea exclusively at night. Symptoms include I hope that it will be clear to you now that Species : Probably Tritonopsilla alba white powdery deposits at the base of the any nudibranchs should be removed from Common name : White nudibranch coral. Gradual erosion can be witnessed the aquarium. (Please do not mistake the also at the base of the coral, sometimes so common Stomatella varia (Figure 10) for a This is my least favourite marine animal severe that the coral becomes detached predatory nudibranch as you will be bar none! Undoubtedly beautiful and yet an from its rock. Tritonopsilla sp. are extremely persistent and well disguised particularly problematic as they have the coral-eating sea slug (Figure 26 & 27). The ability to reproduce asexually and so infest a tank rapidly. As with many of the gastropod molluscs once the problem has been identified, removal is fairly easy although these animals are incredibly well disguised when they surround the base of the coral during the daylight hours bearing a strong resemblance to white the flesh of the coral. Fig 10 Two techniques have been Stomatella sp. Not a nudibranch recommended in the literature for “flushing out” nudibranchs from their hiding places removing a very useful creature from the although both may be stressful for other Fig 26 aquarium!). Tritonopsilla sp. Pink / Orange form aquarium inhabitants. The first involves Figures 29 & 30 show some more turning off all pumps providing flow in the species that commonly occur. Many corals aquarium (not any biological filter pumps). are vulnerable to nudibranchs but the most The subsequent drop in dissolved oxygen commonly infested are button polyps concentration is said to disturb the (Zoanthus spp. and Protopalythoa spp.), nudibranchs and set them on the move. clove star polyps (Anthelia spp.) and Once visible they can be removed with several species of soft coral. Be warned – tweezers. the nudibranch in figure 30 is very difficult The second technique is arguably the to spot! most stressful for reef residents and involves the saturation of the aquarium with tiny air bubbles facilitated by a Fig 29 wooden air-stone or venturi powered Unidentified Nudibranch that feeds on pump. The bubbles irritate the Clavularia sp. nudibranchs and they are forced from their hiding places where the tweezers will again be used to remove them. I have not tried either of these techniques myself, instead relying on Fig 27 Tritonopsilla sp. White form careful checking of specimens prior to introduction and then close observation afterwards. But there are so many well- disguised species that some are liable to slip through the net. Observation at night under blue actinic or torchlight is often the Fig 30 This image shows a best time to nudibranch and illustrates very well Fig 28 Cladiella sp. see these just how difficult they can be to locate

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Class : Bivalvia / Lamellibranchia 6-10cm long mussels that would survive the curing The bivalves are a group of marine and process and provide an freshwater living molluscs defined by interesting display. having a shell that is divided into two parts Unfortunately these days are and usually hinged – for example the clam long gone and now the Tridacna squamosa and the humble but commonest bivalves are small tasty mussel (Mytilus edulis). specimens of approximately 2- Most bivalves have converted their gills 5cm. into a means of trapping and processing One group of bivalves food. The gill area already has its own deserves more than a passing pumping system in the form of the mention here and that is the so- microscopic cilia that create a current of called boring clams of the water that flows over the surface of the gill. family Pholadacea which The bivalves, having enlarged the gill contains the common U.K. surface, are enabling them to process larger species the piddock. Use of the volumes of water and filter out particulate word “boring” is not to suggest Fig 33 Boring clam (about 1cm long) matter such as phytoplankton and that they are uninteresting or zooplankton. If you want to see the dull but that they are capable of enlarged gill surface in the flesh then look burrowing into rock and even at a flame scallop or related animal. Their invertebrates. These are very shells really gape showing the net-like gill common imports; they seem to structure quite clearly. ( Figure 31) survive the curing process in Many reef aquarists will lust after the live rock and also are beautiful Tridacnid clams (Figure 32) but commonly found on the base these are exclusively purchased on their rock beneath corals and polyps. (Figure 33). Their Fig 31 Bivalve mollusc boring action showing paired and much should not cause enlarged gills too much alarm to Fig 34 Tunnels excavated the aquarist but it is in live rock by oring clams. worthy of a Some are still in residence mention as if the animal begins miscellaneous shellfish and they are to be moving through a coral it can welcomed. Many do not even seem to need move much more quickly than supplementary feeding – relying perhaps on through rock and so suddenly it fish waste and detritus for their sustenance may just “pop-out” of a coral although they would probably relish the leaving a neat round hole! prospect of the occasional feeding with Figure 34 shows some live Plancto or other such food. rock that has evidence of I hope you have enjoyed this foray boring clam activity. into the world of the mollusc. I have tried Many other species of to cover the main species that you are bivalve mollusc are to be found likely to find in your reef aquarium. My in reef aquaria. Some have only regret is that I have not been able to own and are mainly derived from culturing been in situ on the rock for so long that provide images and descriptions of all the facilities. However, there are many different years of coralline algal growth and species I have come across in the last five bivalves that can arrive on both live rock colonisation by encrusting organisms means years – there are many. And yes, I’m going and specimen pieces and all can be thought that the shell itself is almost completely to say it one more time – your own of as interesting and harmless additions to obscured. In these cases it is often the vigilance is the key to discovering the true the aquarium. In the days of Florida live presence of the protruding mantle that gives nature of the molluscs in your aquarium – rock many pieces would arrive covered in away their position. This will usually react just think about the number of species that to movement can potentially arrive by accident and keep around it by Fig 32 Tridacna sp. clams your eyes open. disappearing I have also particularly enjoyed as the shell identifying the beneficial species that are to closes. It is be found in aquaria. My research has also very likely uncovered several species, not included that your reef here, that could be of great use to the aquarium aquarist such as scavengers, algal grazers contains and sand-shifting species. Maybe some some of these time in the future aquarists will be able to acquire these species and so achieve an even greater balance in their aquarium.

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