Part 14 Friend Or Foe TRISTAN LOUGHER B.Sc
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Part 14 Friend or Foe TRISTAN LOUGHER B.Sc. graduated from Manchester The Un-segmented worms – University in 1992 with a degree in Zoology. He has PHOTOS BYTHE AUTHOR UNLESS worked at Cheshire Part 2 OTHERWISE STATED Waterlife for five years. o continue our look at the common name suggests, elongate and contents. miscellaneous groups of animals flattened (these characteristics can be used If you suspect that you have one of Tlisted here under the title un- to separate the nemerteans from other Phyla these creatures in your aquarium and you segmented worms we will be taking a brief listed here. A little known fact is that one want to remove it then the best way is look at a number of different phyla. All species of ribbon worm is actually the probably to remove the rock that it calls have the same general characteristics, i.e. longest animal in the world with recorded home. Ribbon worms have incredible they are worm-like in shape, but this does lengths at between 10 and 55 metres! powers of regeneration and can regenerate imply a close relationship between all of (Lineus longissimus) any missing parts if they are damaged in the groups listed here. Indeed, as we will I have unearthed very few of these the removal. Indeed, some species see, many have developed characteristics fascinating creatures in tropical marine reproduce asexually and facilitate this by based on their environment which is a aquaria over the years but they do occur. It breaking at intervals along the body. Each common theme that many worm-like is likely that live rock is the source of most piece of worm then grows the body parts it animals share. individuals experienced by aquarists: I have is missing, such as the head or tail or even found many dead specimens in association both. Phylum Nemertea with newly imported Fijian live rock, but as Ribbon Worms yet, have not yet found a living specimen of this species which is relatively large and black in colour. Ribbon worms are predatory creatures of primarily marine existence (there are some freshwater and terrestrial species) and in this environment they may be found burrowing in sand or rubble or associated with crevices and void spaces in and around rocks. All nemerteans are Figure 2. The image shows what I believe to be a species of predatory and possess a ribbon worm that arrived with some African live rock. I took the specialised proboscis photograph as soon as I spotted the 15cm long specimen but was then called away so I did not have time to remove it and Figure 1. Ribbon worms tend to be which they use to capture examine it closely. elongate, flattened animals which can reach their prey. Although they enormous lengths. Many marine species are do not present a major quite delicate and few survive shipping. threat to reef inhabitants they are known to predate small Phylum Nematoda crustaceans like amphipods which regular Ribbon worms or bootlace worms as some readers of Marine World will recall are The nematode worms temperate species are called are relatively actually beneficial detritivores. Some (Roundworms) abundant animals associated with marine species are known to be egg predators. In We may not be directly familiar with the environments. Numbering about 1150 this situation they use their proboscis to phylum Nematoda, or we at least may not species the ribbon worms are, as their pierce the egg before sucking out the want to admit to knowing too much about 26 • MARINE WORLD – DECEMBER/JANUARY 2004 them but we will have heard of them at well over a million species of nematode least. This is because the nematode worms and make them the largest animal phylum). include several species that are parasitic. Most species are small and many measure For example, Toxocara canis is the less than 1mm. Larger species do exist roundworm we treat our dogs with including the aforementioned Ascaris spp. “wormer” for (Toxocara canis is the species at several centimetres in length. Nematodes affecting cats). The human pinworm, are extremely abundant in every ecosystem. Enterobius vermicularis, affects mainly Densities of a particular species of children and is relatively benign when nematode in one square metre of benthic compared to larger species such as Ascaris mud of the North Sea reached an incredible lumbricoides (as big as a pencil), Wucheria 4 million plus individuals. Barnes (1991) bancrofti (causes elephantiasis) or Loa loa quotes a source from the last century: (The African eyeworm). The lectures in parasitology I took as a student were “If all the matter in the universe always very well attended as the lecturer except the nematodes were swept away, our always had a remarkable set of slides with world would still be recognisable…. which to amaze and repulse us with. There …we should find its mountains, hills, is some sort of morbid fascination with vales, rivers, lakes and oceans represented animals that invade the bodies of others. by a thin film of nematodes” Look at the Alien series of films- we love it! Anyway, before I digress too far the Even if we take this with a pinch of salt it point I am trying to make here is that it is should be almost inconceivable that free- quite possible that we think of nematode living nematodes are not present in our worms only as animal parasites. Well, they aquaria. are also the parasites of plants too! Marine nematodes are held to be the Seriously though, although they may be most primitive of the group and they show encountered in a parasitic role by marine a range of forms which we might not aquarists (given that the majority of the fish necessarily connect with the typical Figure 4. The gastrotrich Urodasys species we keep are still wild caught many roundworm structure. Figure 3 shows an viviparous will harbour internal parasites) free-living illustration of a marine form called forms which are definitely non-parasitic are Desmoscolex which forms part of the much extremely likely to be present in our larger assemblage of animals grouped under sketches of gastrotrichs but have never aquaria. the title Marine Interstitial Fauna. What this found any in my reef aquaria. However, Nematodes are interesting creatures term refers to is the forms of various groups Fossa and Nilsen , have found them in such with a variety of animal which live in the water that a system and perhaps their lack of mention of deviations surrounds individual grains of sand. Marine in most publications rests more with the from the interstitial animals are generally of a similar fact that they have not been looked for than basic worm size (100-200 micrometres in diameter) and their actual absence, and I am perhaps as body plan but elongate. Phyla which include such animals guilty of this is anyone. Densities have nonetheless include flatworms, polychaete worms, been reported at over 1000 individuals in always molluscs, arthropods and, of course 20 ml of sand in intertidal areas where as retaining an nematodes. Many of these animals are to be many as 40 species may be present in any elongate encouraged in the substrates of our aquaria one area. Figure 4 shows the gastrotrich tubular form. even though they will almost certainly Urodasys viviparous: note how similar it is There is some never be seen. Many species are in general body shape to the nematode debate over detritivores and a healthy number of these Desmoscolex. However, unlike the the number of will ensure the well being of substrates nematodes, gastrotrich move around the species including plenums, deep sand beds and our interstitial spaces not by swimming but by currently base sand. creeping around using hair-like cilia. In described Apart from the substrate roundworms order to anchor themselves in shifting (around can be found by the determined aquarist substrates they often have at least two 80,000) and living on live rock and in association with adhesive organs around their “tail” region. those which algae. Many species are more typical in This prevents them from becoming may exist (it form than Desmoscolex often appearing detached from substrate particles when the has been transparent to the naked eye but otherwise sand or mud is moved by, for example, suggested that looking very much like an un-segmented shifting tides. every species earthworm. The diet of gastrotrichs consists of of animal on small particulate matter including single- earth may Phylum Gastrotricha celled protozoans and algae whether they have a are alive or dead and so they may have a A small phylum of mainly interstitial parasitic role to play in the general ecology of specialists inhabiting freshwater and marine nematode marine aquaria. As with almost all of the habitats and even managing to eke out an Figure 3. The worm that is animals listed in this section of the friend or existence on the water film surrounding soil nematode unique to foe series their occurrence in our aquaria Desmoscolex showing particles the gastrotrichs peak in size at each. This may not be immediately apparent, but if in an atypical body form only 4mm and most are considerably residence they may be amongst the most for the phylum would mean smaller than this. I have seen many abundant animals present. MARINE WORLD – DECEMBER/JANUARY 2004 • 27 Phylum Phoronida Horseshoe worms Bibliography and The final worm-like animals we will look at in this suggested further reading edition of Marine World are the horseshoe worms, or Barrett and Yonge. 1985. Guide to the phoronids. This is a tiny group of animals numbering Seashore. Collins.