The Crustaceans Continued Part 9

Friend or Foe Part 9 Friend or Foe The Crustaceans continued TRISTAN LOUGHER B.Sc. graduated from Manchester University in 1992 with a degree in Zoology. He has worked at CheshireWaterlife his article aims to finish our look at for five years. the crustacean families we may Tencounter in reef aquaria, either as hitch-hikers on live rock or in association with the specimen invertebrates imported temperate animals is fundamentally the from many regions of the world. In the same as those we almost certainly will previous two crustacean articles we have experience in marine aquaria. concentrated on large species whose Although capable of swimming the presence is obvious even if they are amphipods we are likely to see scurrying glimpsed only fleetingly. This time we will for cover as the lights go on use their look at the small species, usually less than elongated legs called Pereopods to scuttle 1cm, which can be present in surprisingly Fig 1. Paguritta sp. A specimen that vacated across the substrate. They feed primarily on large numbers in reef, and sometimes, fish- its tube voluntarily but is much more at detritus and consequently are often washed only aquaria. home in Porites sp. hard coral from the surfaces of mechanical filters Before we begin to look at the during routine maintenance. Amphipods individual families it is worth reminding those long antennae have a use – their provide an important food source for many ourselves some of the distinguishing surface area is enlarged by hair-like of our aquarium fish particularly the features of crustaceans. Namely that they projections which, when waved in the water Mandarins (Synchiropus splendidus and S. are segmented, bilaterally-symmetrical column, trap particles of detritus and picturatus) which is why the introduction of animals with two pairs of antennae and plankton which the crab then removes and such fish is recommended for mature articulated legs. With the possible exception eats. The waving motion of the antennae is aquaria with a self-sustaining population of of the sea-spiders (Pyenogonidae) any often the first thing that draws the aquarist’s these small crustaceans. However, it has to insect-like animal you encounter in your eye to these remarkable little crabs. be argued that adding such fish is of reef aquarium is almost certainly a detriment to the reef system as they will crustacean. Sub-order Gammaridea reduce the numbers of a beneficial The last article centred on the true organism thus threatening the establishment crabs from the order Decapoda. Before we of a “balanced” ecosystem. I fully go on to looking at species from different understand why hobbyists want to keep orders I need to tie up a loose end although such beautiful fish but before they stock this group does qualify for inclusion by size them they must be aware of their impact on alone. the reef. Order: Decapoda Sub-order Caprellidae Infraorder: Anomura Puguritta spp. Fig 2. A gammarid amphipod – most likely to be encountered at night or in association Many people purchase pieces of plume rock with mechanical filtration e.g. filter sponges which is also known as Christmas tree worms or Porites. The specimen consists of The largest group of amphipods comprising a colony or Porites hard coral that has been well over 4000 species are the Gammarids bored into by colourful tubeworms. (Fig. 2). Most gammarid amphipods can be However, it can also be home to other recognised by their hump-backs which animals. Barnacles are particularly common Fig 3. Caprellid shrimp – may be less than gives the body a crescent shape when 1cm long in Porites but so too is a decapod viewed from the side. Turn over a stone on crustacean – the Porites hermit crab (Fig the high tide line of rocky shores in the 1). Identified by its long antennae and U.K. and you are likely to be greeted by a Although I have attempted to describe the striped pincers this hermit has given up the mass of jumping amphipods with a shiny most common amphipod species found in roaming life typical of most hermits. brown appearance commonly known as marine aquaria the order has an incredible Instead it occupies vacant tube-worm sand hoppers. The body form of these amount of diversity in terms of shape and tunnels. How does it find its food? Well 20 • MARINE WORLD – FEBRUARY/MARCH 2003 Friend or Foe other characteristics. One such group is the 4000 species of isopod currently known to experience, the parasite seems to cause Sub-order Caprelldae. Caprellids (Fig. 3) science – most are flattened in appearance little or no harm in either the short or long are small shrimp-like amphipods with an and most, like the amphipods, are less than term, discretion may be the better part of elongated body form resembling tiny stick- 2cm in length. Giants exist within this order valour – leave it alone and it will soon be insects. Like the latter their body form is too with another deepwater behemoth gone. adapted from climbing and they possess reaching almost 18” in length – currently Other parasitic isopods may exist in grasping pincers at the ends of their legs the largest described species. Imagine an our aquaria but unseen from our ever- which they use to hold onto algae and 18” long woodlouse! watchful eyes. Some species inhabit the hydrozoans which are home to these Isopods are primarily adapted for a gills of crabs. Others are adapted to share enigmatic little creatures. Very often it is crawling existence and are thus found on the dwellings of hermit crabs. We are their mode of locomotion which attracts the aquarium substrates such as live rock and unlikely to be able to do anything about eye rather than spotting the animal itself. sand where they may feed on algae and such occupations even if we are lucky Caprellids move with a looping action seen detritus. Such species are to be welcomed enough to spot them. in some caterpillars. Some caprellids are in marine aquaria. However, many isopods carnivorous but they are too small to be a are parasitic and one group represented by Order Mysidacea threat to fish or larger crustacean species. Rocinela spp (Fig. 5) is particularly Mysid shrimp Most remove detritus and algae from the alarming for the aquarist. My first surfaces of their host animal or “plant”. experience with this creature occurred some years ago with a Clarki clownfish Superorder Peracarida (Amphiprion clarki). This was a beautiful female specimen that I had had for some Order Isopoda time in an invertebrate system. Suddenly, as if from nowhere, she seemed to be carrying Fig 4. Left: The a hitch-hiker on the top of her head just Fig 6. A mysid shrimp. body form of a behind the eye. The unwanted guest was an Typically reef typical marine isopod – resembling the humble woodlouse specimens measure isopod – very in almost every way – including size. What around 5-10mm and similar to its close could I do? Well, in the tradition of many are semi-transparent. relative the scientists (and more terminal woodlouse. procrastinators) I did nothing in order to see what would happen. The parasite was in We covered the true shrimp of the order situ for almost a week. The bizarre thing Decapoda in the first crustacean focus two was that the anemone fish seemed totally issues ago. Mysids (Fig. 6) resemble true unconcerned by its occupation. When it shrimp and most aquarists are familiar with Below: Actual free- eventually left its host, presumably after them because they are commonly fed in living isopod having its fill of body/blood fluids it left no frozen form to a variety of fish and clue as to its presence – the Clarki was invertebrate species. Almost 800 species are completely unmarked and unphased by the known to exist with the majority inhabiting experience. Since then I have seen several marine environments. The species we are photographs of this isopod, often in most likely to encounter is usually no more residence on clownfish, although they are than 10mm in length and can be located in not specific to this group of fish. There is shaded areas of the aquarium where it will little information about them in the often be swimming in a looping manner literature but about 18 months later the describing a relatively smooth figure of 8 same parasite returned in the same path. Because these small shrimp-like aquarium. Whether it was the same crustaceans have prominent eyes and a individual I cannot say but it did exactly the usually shallow “v” shaped tail region they same thing – remaining in situ for a week are often mistaken for larval fish. Detritus or so then disappearing without a trace. It is is likely to form a large part of their diet in We are all familiar with the largest group of likely that freshwater dips would encourage marine aquaria and they should be terrestrial crustaceans – the woodlice – the isopod to drop off its host but as, in my welcomed by aquarists. They will be even if we didn’t appreciate that they are consumed by fish wherever they can be more closely related to crabs and shrimp caught – dottybacks prove particular adept than the much larger group of terrestrial at this. I know of a hobbyist who did not arthropods – the insects. (I believe that if witness his newly introduced pair of Blue you boil a number of woodlice in a little streak dottybacks feed for over three weeks salted water you can make a passable yet they grew substantially in this time and shrimp-flavoured broth – I must emphasise always looked well fed.

Load more