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Home , Alpheidae, Caridea, Dissodactylus, Eucarida, Hoplocarida, Mantis Shrimp

Friend or Foe

Friend or FoeTRISTAN LOUGHER B.Sc. graduated from Manchester University in 1992 with a Part 7 – The degree in Zoology. He has worked at Cheshire Waterlife for five . DIGITAL IMAGES BY THE AUTHOR

any moons ago I was sitting in a study was to identify all the species of Phylum Arthropoda drab lecture theatre in the life found there. These Crustaceans are part of a larger assemblage University of Manchester’s included several planktonic crustaceans M of called . School of Biological Sciences waiting for called copepods whose classification to means "joint footed" and alludes to the fact the next lecture in the "Invertebrate species level can centre on many features of that all arthropods have jointed appendages Diversity" series as part of my degree their anatomy but to cut a long story short I used primarily for locomotion. Like the course in Zoology. The lecturer then found myself counting the hairs on the legs Annelid polychaetes we looked at in the appeared at the door, uttered the words of these copepods in order to correctly last article, arthropods are segmented but "Crustaceans – too many legs" and then identify them! When you consider that they have one further major adaptation and left! After the initial confusion at the these animals are sometimes only a couple that is the exoskeleton or cuticle. This is a actions of the distinguished Doctor John of millimetres long you can appreciate the usually hard exterior to the ’s body Dalingwater we eventually established that difficulty of this task (and they’ve got loads which affords muscle attachment and the reason for this peculiar behaviour was of legs!) protection. Because this external layer is due to the incredible array of forms within Consequently, in this instalment of the essentially dead it must be shed in order for the assemblage which renders Friend or Foe series I am not going to the animal to grow. In crustaceans and all their classification an absolute nightmare! mention species names unless I am arthropod groups this is done through a This was brought home to me some absolutely certain they are correct. Indeed, process called moulting or ecdysis. In many years later when I was working as part of a in some cases my knowledge is sufficiently groups of arthropod the body form changes research team studying Britain’s deepest sparse for me to attempt to classify them with each successive moulting which makes lake, Loch Morar in the Northwest beyond even their Order assignation. their correct identification that bit more Highlands of Scotland. Part of the project’s difficult. Each individual stage between moultings is termed an Instar.

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Life cycle of a typical 1. Early nauplius 2. Later nauplius 6 3. First protozoea 4. First 5. First post-larva 6. Adult shrimp

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18 • MARINE WORLD – OCTOBER/NOVEMBER 2002 Friend or Foe

Sub-phylum Chelicerata on their body segments plus for respiration under water. The Chelicerates are a group which Chelicera contains only one sub-class that the marine aquarist is likely to come across by Class Cirripedia Body accident in a reef aquarium, and a single No sooner have I declared that I will species that they may purchase. This Sub- concentrate on large crustaceans in phylum’s name comes from the specialised this article I immediately start with a feeding structures termed chelicerae which Leg group of animals that are usually can be alikened to the pincers of . smaller than the 10mm maxiumum The main characteristic that separates this size! This is for good reason as the group from other arthropods is their lack Cirripedia represent a group of of antennae. crustaceans that are significantly (one million described species) than the Chelicerates include the extinct Trilobites, different from the rest of the crustacea. Crustacea. Taxonomists believe that spiders, mites, scorpions and little known Many temperate species do not reach more crustaceans are amongst the most primitive groups such as spiders and whip than 5mm in diameter but it is common to extant arthropods due to the vast majority scorpions. have accidental imports reaching our of species retaining the ancestral marine It is important to recognise that these minimum size. We know them as barnacles existence. Perhaps one of the reasons the are distinct groups from the crustaceans and they represent a group of crustaceans crustaceans have had continued success for with which they share a common ancestor that have given up the ability to move many millions of years is the fact that but, for example, the extinct trilobites did freely. Instead, they remain in a fixed insects have not conquered this not evolve into anything else, they simply position with the body surrounded by a environment. Most of the insects died out. number of calcium carbonate plates. This encountered on rocky shores in the U.K. are means that a barnacle must rely on food to primitive species that are not truly aquatic reach it. Thus we find them associated with Subclass Xiphosaura and will die if submerged for long periods. areas with a strong flow and/or much Common Name : Horseshoe crabs An aquatic existence opens many niches for suspended food particles such as phyto or Latin Name : Limulus polyphemus crustaceans. For example, they can achieve . By using barnacles as a guide The Horseshoe crabs are often referred to larger sizes due to the buoyancy provided we can deduce the type of area a specimen as "living fossils" due to their ancient by water. came from. ancestry and primitive looks. There are four Because of the space limitations I must Barnacles have specialised feet – the known species belonging to 3 genera. adhere to this article I will include some of name cirripede means "hair foot" and they Limulus polyphemus is the American the larger crustacean species that can be use the fan-like feet to collect food. Sessile species, the other three are Asian. encountered by aquarists. Subsequent barnacle are called Balanomorphs and it is Horseshoe crabs are generally kept by articles will continue this theme and then these that are most prevalent in our aquaria aquarists requiring them for their novelty will focus on some of the smaller and more and can be recognised by their distinctive value or indeed in a sand-shifting role. unusual species of crustacean that one may shape. Some species are found in Their spade-shaped acts like a experience. association with hard corals such as Porites plough as it shuffles through the sand. This The defining feature of crustaceans is sp. and Euphyllia spp. It is likely that the is a fascinating creature but as marine that they all possess two pairs of antennae corals have overgrown specimens in these aquarists will only acquire this species by on the head. Insects have a single pair, cases but due to the repeated feeding purchasing it there is no need for further spiders and their allies have none. Most actions of the barnacle they are not capable description here. species also have a number of appendages Sub-class Pycnogonida Common Name : Sea Spiders This group of chelicerates is given its common name due to the fact that most species have 8 walking legs much like spiders. However, they are a strange group that most aquarists may overlook or never experience in their aquarium as they are liable to be short lived and usually very small (<10mm). I have found several dead specimens in association with Live Rock but am yet to see a living one in an aquarium situation. They can be found feeding on bryozoans, colonial anemones and other encrusting organisms but are easily removed if so desired. Sub-phylum : Crustacea Crustaceans are the second largest sub- division of the Arthropod Phylum with Two 15mm diameter barnacles slightly obscured by Disc anemones. This picture was taken around 38,000 described species. Only the just after the lights came on for the first time. Only a few minutes later the barnacles were insects have a greater number of species smothered thus any attempts at feeding had to occur when the lights were off.

MARINE WORLD – OCTOBER/NOVEMBER 2002 • 19 Friend or Foe

of smothering the barnacle completely. that severe as the The head and thoracic region of a . This works to the barnacle’s advantage as it chances of the parasite This is a "smasher". Note the very large compound is obscured from attack by many of its becoming fertilised are eyes and club-like second appendage which are a enemies plus the stinging cells of the corals small but they can be pale purple colour in this species. provide an excellent deterrent for creeping avoided completely by predators such as whelks which enjoy careful scrutiny of any nothing better than drilling a hole in the purchases barnacle and sucking out the contents. particularly porcelain Have a look at Plume rock (Porites sp.) as crabs ( along with the abundant tubeworms it is spp.). not uncommon to have barnacles present. Due to their feeding habits barnacles Class are unlikely to survive for long in marine aquaria unless they are supplied with sufficient particulate food such as Plancto Malacostracans make or Marine Snow. Most species of barnacle up the majority of are entirely harmless but it is worth species within the mentioning a group which, although Crustacea with over unlikely to bother the aquarist greatly, may 22,500 species one thing straight. If you hear a sound like present a significant problem to the other currently described by science. Most of the cracking or splitting glass, or a metallic crustacean inhabitants of the aquarium. larger forms are represented within this click this is extremely unlikely to be a class although the size extremes range from mantis shrimp. What you generally have is the largest arthropod of them all; Parasitic Barnacles a pistol shrimp (see below). When a mantis Macrocheira kaempferi, the Japanese Many species of barnacles live shrimp strikes its prey it makes a much spider crab with a bulk so great its legs commensally on other animals. Some duller, less sharp sound. Plus, you are much cannot support it out of water, to the pea species are found only on the tough skin of more likely to see a mantis shrimp than a crabs such as Dissodactylus at 4mm whales whereas others will settle on sea pistol shrimp and be able to make a maximum size. The group also contains the urchin spines or to name but a few. positive ID based on their most obvious hermit crabs, shrimp, true crabs, Other species can be found on corals features: gammarids and other more obscure including gorgonians where the marine assemblages. aquarist may find he/she experiences them Not a great photograph frequently. Generally speaking, these have but a typical shot of a no significant impact on their "hosts", Subclass mantis shrimp as you neither good nor bad (although one could Order Stomatopoda might experience it in argue that the "fouling" of a whale with Common name : Mantis an aquarium - a pair of barnacles could increase the amount of There is no other two words that when put antennae and a pair of drag it experiences and therefore reduce its together strike fear through the hearts of big compound eyes swimming efficiency – studies of boats poking out of a hole. marine aquarists like mantis and shrimp. This little chap doesn’t miss a thing. fouled by barnacles have shown that some They have been ruthlessly pursued by 30% reduction in fuel economy can be reefkeepers for years due to their penchant experienced.) Some species have evolved for killing the odd and crab. I don’t A mantis shrimp has two very large eyes into parasites however and rely on their wish to excuse their behaviour but we need which afford great vision. It also has a long hosts to provide them with food. to clear up a few things about these body with a number of appendages beneath The Rhizocaphalidae are parasitic on troublesome terrors. Firstly, I have which it uses to propel itself at high speeds many types of crustaceans – particularly experienced several instances when an across rock and sand surfaces. Perhaps the crabs and their relatives. The larval aquarist has been convinced that his/her most obvious feature is the pair of enlarged barnacle arrives and enters the crab though aquarium has such a shrimp in residence thoracic appendages. The structure of these a convenient opening such as a due to a loud clicking sound. Now, let’s get divides the mantis shrimps into two distinct aperture. Development usually occurs categories – beneath the tail in true crabs and the smashers hermit crabs where it appears as a A specimen measuring around 10cm and the non-granular, amorphous presence, spearers. yellow-brown in colour.A granular Smashers mass in this position is likely to be an have egg mass and will only be carried by enlarged and females. The barnacle, as it matures, very solidly sends out nutrient absorbing structures constructed throughout the body of the crab called appendages the interna. Presence of these and of that remain the barnacle itself can be quite folded when debilitating to the host and result in, they strike. amongst other things, sterilisation and They are inhibition of moulting. The capable of ramifications for other crustaceans breaking the sharing an aquarium with a parasitic shells and barnacle and its host are probably not of

20 • MARINE WORLD – OCTOBER/NOVEMBER 2002 Friend or Foe

and crabs which they hunt for food. experienced loud snapping sounds made by as , corals and anemones. Many Spearers unfold the appendages as they individuals only 10mm long! aquarists will be aware of the symbiotic strike releasing the barbed terminal digit relationship between which punctures the flesh of the primarily Alpheid shrimps and so- fish prey. called watchman or It goes without saying that either of gobies e.g. these types of mantis shrimp is undesirable sp. The for the but this should not relationship is a mean that any you manage to remove relatively simple one. should be killed. Indeed, mantis shrimps Many pistol shrimps can make excellent pets in their own right have poor eyesight but and a small aquarium set up for them alone can dig excellent can be very rewarding. burrows and tunnels. In order to remove a mantis shrimp Watchman gobies have from your aquarium you must be extremely excellent eyesight and vigilant. Unsuccessful attempts at trapping can provide an early will only serve to educate your quarry and warning of approaching repeated attempts with the same technique predators but they have are unlikely to be successful. The easiest no tunnelling skills. Thus way by far is to remove the rock that the by sharing the retreat shrimp has chosen as its home. both the fish and the Part of the reason that people get shrimp have something mixed up between mantis and pistol shrimp to gain. is that the latter produces a clicking sound I am a great fan of pistol akin to that of breaking glass whereas the shrimp as they are one of mantis shrimp is capable of actually the crustacean groups A 1cm pistol shrimp. This is the size at which most specimens breaking glass up to 1/4 inch thick! This is arrive in aquarists aquaria. You may notice that this specimen has that will be completely unlikely to happen in an aquarium as the relatively much larger, better developed eyes than the previous at home in a reef shrimp has no need to break the glass, and individual which appears to be a characteristic of free living species. aquarium. Their tireless most glass will be too thick anyway. But work in improving their remember, these animals did not get their The clicking sound of pistol shrimps is burrow is fascinating to watch particularly nickname of "thumbsplitters" for nothing! generated by an enlarged pincer. The if a goby is in residence too. As with all shrimp "winds up" the movable part of the crustaceans, a pistol shrimp is unlikely to Subclass pincer by contracting strong muscles turn down an easy protein meal so slow housed in the overdeveloped claw. This moving or injured/poorly fish are Superorder then fits into a notch ready to fire. When potentially threatened by such a shrimp but Order ready to click another muscle pulls the claw I have never experienced any problems Infraorder out of its notch where the muscle tension with any of the numerous specimens I have Family : pulls it back to meet its opposing claw. kept. One of the only problems with the Common Name : Pistol or snapping When they meet the loud cracking sound is introduction of these fascinating creatures is shrimp produced. The shrimp that they often decide to set up home where usually uses this in you can’t see them! defence as it can be so Enlarged pincer for generating “clicking” loud and piercing that Order Decapoda noise potential aggressors can Suborder be stunned or at least Infraorder Palinura Smaller recessed eyes deterred. Large Family : Scyllaridae individuals may use the Common Name : Spanish or slipper snapping sound for lobsters but I am yet to In a world of bizarre crustaceans this family experience this in a still manages to throw up some even more home aquarium. remarkable body forms. The slipper lobsters Features of a burrow digging pistol shrimp. Pistol shrimps are the bulldozers of the crustaceans world This species is a inhabit holes, tunnels due to their modified antennae which are common import and will prove a hardy and Illustration reproduced from a photograph taken from the subject’s interesting specimen. above right

Flattened Despite being regularly confused with the and crevices in mantis shrimp the members of the Family Hard carapace the aquarium in Alpheidae are one of the commonest large addition to the Typical -like tail crustaceans experienced by marine species that live aquarists as accidental arrivals. Many in association species encountered are over 2-3cm long with other when first noticed visually by their such unwitting new host. However, I have Illustration of the body shape of a typical

MARINE WORLD – OCTOBER/NOVEMBER 2002 • 21 Friend or Foe flattened and resemble a shovel. The crabs as in times gone by but these This article has been a mere antennae are used to move sand and rubble fascinating little crustaceans can still be in pursuit of their prey which can consist of obtained from dealers. Porcelain crabs are taster of what the polychaete worms, molluscs and even small not true crabs – they are related much more crustacean world has to sea urchins. closely to the squat lobsters. The main clue Slipper lobsters are shy creatures to this is the use of the tail in rapid offer us in the way of seldom venturing into the open during the locomotion. True crabs have relatively day and so it was with some great fortune immobile tails whereas the porcelains can marine hitch-hikers. The that I spotted one retreating into its hole in use their broader tails to swim – as anyone next article will focus on a piece of African live rock. This is a very who has dropped one into an aquarium will unusual find but so far I have been unable tell you. The widely kept anemone crabs the True crabs or to coax it into the open for long enough to are species of porcelain crab that have Brachyurans of which take a photograph so the diagram will have adapted to life in or around anemones. This to suffice. Although this animal will not affords decent protection when feeding several species are present a problem to your aquarium it will which can expose the crabs to danger. This represented in marine grow large and so should be removed alive is because porcelain crabs are primarily and transferred to an aquarium with plenty filter feeders. One of their maxillipeds (the aquaria. of room and large pieces of rock that cheliped) has a specialised structure in the cannot be undermined by its foraging form of a bristly fan which catches behaviour. upon which the animal feeds although larger pieces of "fishy" food will Order Decapoda be accepted in the aquarium. As a result Suborder Pleocyemata they are ideal inhabitants for almost every InfraorderAnomura marine aquarium. But, a word of warning, Superfamily Galathoidea do not mistake a free-living porcelain crab Family Porcellanidae for an anemone crab. I have heard of a Common Name : Porcelain Crabs couple of instances where free-living specimens have been placed caringly in the Once a very common import along with centre of a carpet anemone which has taken live rock from Florida and the Caribbean great pleasure in eating the poor thing. If in we don’t see as many free-living porcelain doubt, let the crab find the anemone on its own.

Feeding arm (Cheliped)

Flattended Pincer

Folded cleaning leg

Long Antenna

Broad tail Bibliography and suggested further reading • Barrett and Yonge. 1985. Guide to the Seashore. Collins. Dorsal view of the • Debelius 1999. Crustacea Guide of the Anemone/Porcelain crab World. Ikan Publishing • Debelius and Baensch 1994. Marine Atlas Vol I. Mergus Publishing. • Fossa & Neilson. 2000. The Modern Flattended Pincer Aquarium. Vol 3. Birgit Schmettkamp Verlag. Feeding arm • J.G.Walls (Ed.). 1982. Encyclopedia of (Cheliped) Marine Invertebrates. T.F.H. Publications 3 pairs walking legs • Ruppert and Barnes. 1994. Invertebrate Zoology Sixth Edition. Saunders College Broad tail Publishing • Sprung. 2001. Invertebrates – A quick reference guide. Ricordea publishing. Acknowledgements Ventral view of Anemone / Lisa Birchall for illustrations. Porcelain crab-tail unfolded Mark Scott for specimen provision

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