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. 30 • MARINE WORLD – JUNE/JULY 2002 Friend or Foe 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 MARINE WORLD – JUNE/JULY 2002 • 31 Friend or Foe 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).