Friend or Foe

Part 10 Friend or Foe The – Part 1 TRISTAN LOUGHER B.Sc. graduated from Manchester University in 1992 with a he phylum Echinodermata contains Another important feature of degree in Zoology. He has several species familiar to many echinoderms is their water-vascular system worked at CheshireWaterlife Tpeople – how many children don’t used in locomotion and food acquisition. for five years. know what a looks like? However, We can see the tube feet of starfish on their there are many members of this assemblage underside and often all over the surface of that are not so well known and some may sea urchins – both are governed by the be encountered by marine aquarists. Before water-vascular system. Brittle stars lack we go on to look at individual species we tube feet but their highly mobile arms are expect to encounter in a live rock based will cover some of the unique attributes of powered by the same system as other reef aquarium although accidental echinoderms. echinoderms. Damage to this specialised introduction is not out of the question. system has been blamed for lack of success Classes with some starfish in captivity. Class Asteroidea Echinoderms are said to show Asteroidea – True starfish pentamerous symmetry – that is they are – True Starfish Ophiuroidea – Brittle starfish essentially made up of five similar True starfish have a variety of forms with Holothuridea – Sea cucumbers segments. Humans, insects, crustaceans, the average number of arms being five but Crinoidea – Feather starfish / Crinoids flatworms etc are bilaterally symmetrical. up to fifty are possessed by some species. Echinoidea – Sea urchins/ Sand dollars/ Sea That is, the left side of our body is almost In other species arms have become so potato etc. identical to the right. I say almost because shortened that the resembles a we are not totally symmetrical – there are pentagon shaped pillow. Correct Echinoderm means literally "spiny skin". several studies going on around the world identification of closely related species is This characteristic is due to the unique which hope to gain support for the theory not straightforward and the taxonomist may internal skeletal structure found in all that find symmetry attractive – the have to resort to dissection to be absolutely echinoderms, consisting of calcareous more symmetrical your appearance, sure of what they have. ossicles, which are articulated in sea stars whether it be wing length, facial One of the problems with starfish, and rigid in sea urchins and contains a type proportions or patterning, the more however small, is that prey doesn’t have to of tissue termed mutable connective tissue. attractive to the opposite sex you are. fit inside their mouths to be consumed. This can determine the rigidity of the Irrelevant here but interesting nonetheless! Starfish are capable of everting their echinoderms’body and is especially useful Echinoderms number for animals that utilise its versatility. For some 6000 described example some starfish need to be species divided into 5 Basket starfish manoeuvrable and flexible but then when further classes as listed predating on hard shelled animals they may above. Of these the brittle need a degree of rigidity when attempting stars have the most living to prise the bivalve open. As aquarists we species although the fossil can experience the incredible nature of record demonstrates that mutable connective tissue by observing sea crinoids were extremely cucumbers – a group of echinoderms. Sea numerous and diverse apples in particular can inflate themselves many millions of years up to relatively huge sizes (from tennis ball ago. Comatulid sea stars to football) in no time at all. It is reported or "feather starfish" are that vigorous rubbing of a sea cucumber sometimes purchased by causes the tissue to become almost liquid – aquarists due to their literally flowing through your fingers. Of beautiful colouration. course, this begs the question – why on However, they are not earth would you want to do this but it is an suitable for the vast interesting phenomenon nonetheless. majority of marine Brittle starfish also exploit the properties of aquaria and should be such tissue by shedding their arms when avoided. Crinoids are threatened – a phenomenon termed perhaps the only autotomy. echinoderms we might not

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stomachs and digesting whatever they are pest resting on. Thus large corals can be stripped population Linckia sp., Leiaster sp. and Echinaster sp.. Note the different colours but also two dark of tissue with relative ease. being purple individuals are the same species but Fortunately, few asteroid starfish make controlled have different numbers of legs. Five is the their way into reef aquaria as accidental rather than norm but the individual bottom centre has introductions. Those that do are likely to be eradicated – six. from the following genus. thus the pest species must Genus: Asterina always be present These small starfish are termed "cushion albeit in stars" due to their chunky appearance and small quite short arms. Colours vary and are not a numbers – reliable means of identification but the ok if you unifying feature of the species we don’t mind a encounter regularly in our aquaria is the few of your slightly "chewed" look – almost as if corals being something has been nibbling their legs! The scoffed numbers of legs vary although five appears rather than to be average. In the U.K. we have an all of them. Asterina species called the common We have cushion starfish. This species is unusual in seen this that it is not a broadcast spawner like most situation of the rest of the true starfish; instead eggs before with are laid under stones and rocks. If this is the nudibranch Chelidoneura varia that Thus counting legs is an unreliable true of the reef specimens then this could predates flatworms such as Convolutriloba identification technique. explain why this species seems to thrive in retrogemma. Once the pest population is Many aquarists experience problems aquarium situations although they are also drastically reduced the predator population with starfish within a relatively short time. said to reproduce through fission i.e. the starves to death. Then the risk is that the Many specimens seem to disintegrate, splitting of the body into two. pest population recovers or further pests are sometimes very rapidly, sometimes over a There are reported to be three species reintroduced. I believe that in this scenario period of weeks. Reasons for this are of Asterina that are commonly imported such a control technique is unethical but unclear. Many aquarists first believe that with live rock. The 0.5cm, whitish ones there could be scope for perhaps sharing this is the result of an attack by a appear to be pure algal feeders. This is the predators amongst aquarists (good luck in crustacean or bristleworm but this is species we are most likely to experience in catching the shrimp!). The other alternative extremely unlikely to be the cause, our reef aquaria. There are two other is to culture Asterina elsewhere and feed although such animals could scavenge species that I have only seen in reference your shrimp with them. partially damaged specimens. Some sources books. One is vivid green and the other Of course, it almost goes without state that it is due to poor handling and 1cm+ across the arms at maximum size. saying that there must be no other starfish shipping, others that it is due to diet. It is Both of these species are reported to species present as these are likely to be possible that both causes produce similar predate hard and soft corals. Thus only attacked also! symptoms but the experiences with these prolonged observation of any suspicious- Starfish have remarkable powers of animals lead many aquarists to believe that looking specimens will determine what you regeneration. Most species are capable of all starfish are sensitive. have. Indiscriminate removal will ease your regrowing an arm; some detached arms are Apart from the different Asterina fears but have you just dumped something capable of regrowing a complete animal. species another type almost guaranteed to quite useful? Sometimes we experience individuals from do well is a species of sand-shifting starfish a species that usually has only five arms – probably a member of the genus Control of harmful species but they have six, or four or more or less! Asteropecten. These animals have become Given the potential for reproduction that Asterina shows in reef aquaria it is unlikely that the aquarist will ever control nuisance or harmful species of starfish by manually removing them, although this may be a valid technique if you can identify a potential problem early enough. One technique of biological control has been suggested involving the use of the Harlequin shrimp (Hymenocerca elegans). These beautiful crustaceans are obligate starfish eaters and so will ignore other foods. Asterina spp. are on the list of suitable foodstuffs for this shrimp but simply adding this species to your reef and expecting problems to disappear is naive. Biological control can work very well in a Fromia nodosa. Maldives starfish showing tissue necrosis after seeming to "blow apart". This variety of situations but always relies on a phenomenon is very unlikely to be caused by predation.

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separation of legs in the aquarium. There’s not a lot you can from the body. As say about comments like that is there? The an escape response class, Ophiuroidea does contain a group this mirrors the which are the exceptions to the rule – the tactic used by basket starfish. These filter-feeding animals several lizard have arms which are branched to the extent species and the that they resemble fine lace when extended. snail Stomatella Sometimes available in the hobby they are varia and leaves not suitable for most aquaria unless specific the potential attention and daily feeds are given. predator with a Most of the species we encounter are twitching morsel very small, however, we are often tempted while the victim to purchase larger specimens as they have a makes off rapidly useful role in detritus consumption. I prefer and relatively the sand shifters for this, as some species of unscathed. The brittle star are not as innocuous as they first brittle star then appear. For example the Green brittle star, regrows a new Ophiarachna incrassata, is a commonly arm. Brittle stars kept species that can breed readily in home are perhaps the aquaria. It performs a useful role in many most abundant of aquaria, as it will take uneaten food from all echinoderms the substrate and becomes very tame with that arrive by time. However, this species has a sinister accident in reef side too. Each arm is lined with elongated aquaria. Figure 1 spines, similar to those in other species. Figure 1. Assorted brittlestars from the rock to which a soft coral was attached Shows several However, used in the right way the starfish individuals that is in possession of an excellent trapping increasingly available over the past few arrived on a single mechanism. Lifting its circular body clear years and many aquarists are using them to piece of soft coral – and these control detritus build up in their sand which were only the ones that left the Sand shifting starfish can, if ignored, lead to cyanobacterial rock, more may have been blooms (slime algae). lurking inside. The good news It is worth checking any newly is that the vast majority of such acquired starfish specimens for other specimens are totally harmless organisms. They can be home to several and can be encouraged. Some commensal and parasitic organisms species, such as Amphioplus, including copepods, bristleworms and reproduce asexually and reach molluscs such as Thyca spp., which we great numbers if conditions mentioned in the mollusc section of the suit. More about this species Friend or Foe series. later. Identifying a brittle star as such is relatively easy as they Class Ophiuroidea – usually have a circular body The Brittle stars with thin arms that taper This, the largest class of echinoderms, towards their end. However, I numbering over 2000 species, gets its have heard some references by common name from the fact that careless the less interested visitors to handling or threat of predation causes the our premises to "the octopus"

from the substrate the brittle star forms a shaded area which seems to appeal to fish which move innocently underneath. The brittle star detects this and springs its trap, moving quickly downwards and bringing the legs together. The spines form a cage and the fish, if it has not been alert enough, is doomed. It’s interesting to note here that older books don’t mention the undesirable habits of this species and it is recommended unreservedly by some. Genus Amphioplus Perhaps the most common of the accidentally imported brittle stars belong to Green brittle star – watch your gobies don’t become ensnared the genus Amphioplus. These are often

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Genera Ophioderma and Ophiolepsis Bibliography and suggested further reading Barrett and Yonge. 1985. Guide to the Seashore. Collins. Debelius 1999. Crustacea Guide of the World. Ikan Publishing Debelius and Baensch 1994. Marine Atlas Vol I. Mergus Publishing. Debelius and Baensch 1994. Marine Atlas Vol III. Mergus Publishing Fossa & Nilsen. 2000. The Modern Coral Reef Aquarium. Vol 3. Birgit Schmettkamp Verlag. J.G.Walls (Ed.). 1982. Encyclopaedia of Marine Invertebrates. T.F.H. Publications Ruppert and Barnes. 1994. Invertebrate Zoology Sixth Edition. Saunders College Publishing Sprung. 2001. Invertebrates – A quick reference guide. Ricordea publishing misidentified as bristleworms as only their is not inconceivable that members of these you can have, others say that they represent black and white banded arms are usually genera might arrive associated with coral a potential hazard to fish. The vast majority visible as they extend them in the hope of base rock. They are certainly commonly of specimens I have experienced, including trapping detritus from the water column. imported with live rock but unfortunately some very large Red serpent starfish The arms are usually no more than a do not survive the shipping process. Legs (Ophioderma squamosissimus) have proved centimetre or so in length and the body is are very bristly and colour is variable from safe. The individual in the image above was rarely seen, tucked away in holes and black to white and many colours of the only quite small and almost certainly will crevices in live rock or coral base rock. rainbow. They are beneficial creatures prove a lucky acquisition for whoever This species is almost certainly capable of which feed on fish faeces, uneaten fish food purchased the coral it arrived with. asexual reproduction as in favourable and detritus. This is the end of our first look at the conditions its numbers explode. It should The serpent starfish are so called echinoderms. In the next article we will be considered totally harmless and because their plain, unbristled arms snake look at the other classes in this phylum – beneficial in the trapping of suspended along the substrate in search of food. The the sea urchins and sea cucumbers. detritus. jury appears to be out with regard to their usefulness in reef aquaria. Some authorities Genus Ophiothrix state they are among the best scavengers The sponge and soft coral dwelling brittle stars are relatively common imports but are Brittlestar Ophiocoma sp. unlikely to be encountered by large numbers of marine aquarists as the hosts of this echinoderm are not favoured by many aquarists due to their demands. Gorgonians, Dendronepthya soft coral and sponges are the commonest hosts and those that are home to this species generally do not photosynthesise and rely on their nourishment form feeding on phyto- and zooplankton or marine snow. This gives a clue to the dietary preferences of the Brittle star – it is believed that it removes particulate matter from the surface of its host rather than preying on the host itself. These starfish have a beautiful colouration and their upkeep could be attempted in the absence of their hosts provided suitable food is offered. Genera Ophiocoma and Ophionereis Although unlikely to be encountered by most aquarists as accidental acquisitions it

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