Due to international rules, the systematics of animals is mostly presented in English and Latin or Greece. Every living being on our planet can be assigned its place in this system. The best way to imagine this system is as a large shelf with many niches that have certain designations and in which the corresponding creatures can be sorted. However, Carl Linne's original system has been expanded and improved many times in the meantime, as more and more animals and plants have been discovered, that cannot be classified into simple categories, as they often move systematically between different gradations or represent transitional forms. In the example above, the scientist and year to which each stage is to be assigned was indicated behind it. This shows that the taxonomy of living organisms can still change and expand; therefore, this system must not be understood as a rigid static structure. Rather, the structure grows with the state of research, and it is conceivable that the example shown above will need twice as much space in a hundred years' time, viewed from top to bottom, because even more fine gradations have been added. I consider it particularly important to indicate the name of the first describer of a species and the corresponding date of the description after the Latin double name, because one can only assume a secure species if one has found these dates. Unfortunately, some species and/or genera are checked and revised again and again, so that one can never assume that the result of a determination will last forever. Therefore, if you want to maintain a professional collection, you should always check the topicality of the nomenclature at intervals of a few years with the help of up-to-date internet sites. For this purpose I particularly recommend the use of ZIPCODEZOO.COM. If possible, one should prefer official sites of the respective universities and always take into account that even the experts unfortunately do not agree on some things so quickly and in some cases even publish different data. In my excerpt from the Systematics of Arthropods, I myself have divided the Anomura into Anomura I and Anomura II, because I think it is likely, that a revision will still be made in this area. This is because Hermit Crabs on the one hand and porcelain and King Crabs on the other show very considerable morphological variations, so that one has to wonder here whether the classification of these animals in the same order is correct. It is my hope that molecular genetics will provide new results on this in the near future. And that taxonomists do not invent more taxa that complicate the systematics even more... Finally, it should be noted that the concept of species in biology is unfortunately not clearly defined at present. Molecular geneticists are arguing with morphologists and others; the outcome is uncertain. Is there any objective truth here at all? Probably everything is in flux at the moment! Only one thing is certain: it is not as simple as we were taught in school thirty years ago. We now know that species evolve from other species. And that in some cases even apparently different species can interbreed and produce fertile offspring. Until recently, this was considered an important criterion for species delimitation. It is possible that the importance of molecular genetic analyses is simply overestimated or even misinterpreted at the moment. Therefore, not everything that comes from this branch of research should immediately be considered objective and true. After all, the scientists of this faction could ultimately be just as addicted to profiling as their colleagues were in Carl Linnes` days. And unfortunately, it is also a deplorable shortcoming, that research work nowadays tends to be project- and goal-oriented. Because research also costs money, of course, and hardly anyone can work for free or for God`s wages. As a result, today's scientific world is not opinion-neutral or independent, which is why it often adopts the premises of its clients. This then distorts the results accordingly. So one should not be too faithful to science and better not expect value-neutral objectivity. On the other hand, you can also become a researcher yourself by writing down your observations and communicating them to others. In this way, even hobby researchers can often make a valuable contribution that is above all not unobjective due to commercial requirements. (Some hobbyists have even described new species). Become an unbiased nature researcher, too!

Keeping crayfish in aquaria

Let's be realistic: we will never succeed in recreating nature's model 100 per cent in our aquaria. All we can do is to make life in the aquarium as pleasant as possible for our animals, so that they feel completely at ease and also reproduce here. In doing so, it may be, that what is not pleasing to the eye is ideal for the animals and vice versa. On the one hand, crayfish do not like sterile aquaria that always look clean and tidy, as if a cleaning fairy had been at work only yesterday, but on the other hand, the question of water quality should not be neglected. I would therefore describe optimal crayfish tanks as being characterised on the one hand by consistently good filtration and regular water changes, but on the other hand also by a wealth of structures, cover and retreat possibilities for the animals and by well-kept detritus accumulations in certain places. My crayfish aquaria are usually set up according to the same basic idea, which I would like to briefly introduce here. But let's start with the substrate: I prefer layers of fine sand, whereby the layer height of the sand can be up to 10 centimetres or more. In this concept, the substrate is also used as a filter. With a substrate placed in this way, three layers form after a short time, which are important for water purification. The uppermost layer up to a depth of about 5 centimetres can be described as an oxic layer, in which there is still a relatively high oxygen content. - This is followed by a suboxic layer, which runs from about 5 centimetres to 8 centimetres deep and already contains considerably less oxygen. Below this is an anoxic layer, in which numerous anaerobic bacteria live, which utilise the metabolic waste products of other organisms. This layer in particular acts like a natural sewage treatment plant and breaks down nitrate. Blue-black bacterial discolouration often occurs in this layer. Especially in this lowest anaerobic zone, nitrate is split into pure nitrogen and pure oxygen by the anaerobic bacteria groups, so that an enormous nitrate decomposition takes place. Gas bubbles form in the substrate, which leave the aquarium after a while via the water surface. The older this substrate gets, the higher its biological efficiency. The main advantage over other substrate materials, such as gravel, is, that due to the fineness of the sand, it is relatively difficult for organic waste to penetrate these anoxic layers, so that no foci of putrefaction with sulphates (sulphur compounds) can form here. Another advantage of sand is, that it is a very inexpensive substrate that can be partially vacuumed out and renewed at any time. I have found commercially available bird sand, from which I rinsed out the aniseed oil before using it at home, to be a good choice. Parrot sand, on the other hand, should not be used, because it contains caustic lime, which unfortunately makes it unusable for aquarium purposes. Once you have created such a biologically functional substrate, you no longer need any elaborate filter systems, because the substrate already performs this function. Nevertheless, the strongest possible water circulation should be ensured by one or more pumps. In my crayfish tanks, the external filter of the brand "EHEIM-Liberty" has proved particularly effective, as it brings a strong, adjustable current into the water and at the same time removes considerable amounts of organic waste from the aquarium through easy-to-clean filter cartridges, so that it can be taken out of the water cycle. Another function of the sandy bottom, that should not be underestimated, is, that the crayfish can also occupy themselves sensibly here - just like in nature - by digging. I am convinced, that some animals become aggressive in the aquarium, because they do not have these opportunities to occupy themselves. Therefore, one should tolerate the redecoration of the tanks by the crayfish within certain limits. All structures in a crayfish aquarium should be built in such a way that the crayfish cannot bring them down. If larger stones are to be used, they should be placed on polystyrene or Plexiglas sheets to prevent the bottom from cracking. This is especially true when keeping larger crayfish species, which can reach final sizes of 10 centimetres and more. I think planting is rather unsuitable for most crayfish tanks, as most crayfish regard plants as food. You can help yourself with foliage and plastic plants. Foliage is a staple food of most crayfish anyway and promotes their health, as beech foliage, for example, contains substances that act like antibiotics. And many crayfish species also like waterweed very much. These natural foods contain numerous vitamins and dietary fibres that significantly increase the vitality of the animals. Conversely, the absence of these nutrients can produce pigment deficiency and moulting problems. Therefore, you should always make every effort to provide your pets with the best possible nutrition.