Silverfish ( Lepisma saccharina )
|Borner , 1904|
The fish (Zygentoma) are an order of the insects (Insecta). Of the approximately 470 known species, six are common in Central Europe. Most are seven to fifteen millimeters long, the species Stylifera galapagoensis , which is widespread on the Galápagos Islands , reaches a total length of about 20 millimeters (without tail appendages). The Squamatinia algharbica , which lives in southern Portuguese caves , reaches around 30 millimeters, with antennae on the head and end of the body around 10 centimeters . This species is the "largest underground insect in Europe".
The head is directed obliquely forward (prognathic to hypognathic) and always has biting and chewing mouthparts. The five-part buttons of the maxilla ( lower jaw buttons ) are noticeably elongated, while the four-part buttons of the labium ( lip buttons ) are inconspicuous. On the head there is a pair of elongated, multi-segmented antennae that can reach about body length, as well as two small complex eyes composed of only a few ommatidia, which are completely absent in the subterranean species. Forehead eyes (ocelles) are only present in Tricholepidion gertschi , the only representative of the Lepidotrichidae (see below).
The body of the fish is flattened. The three segments of the trunk ( thorax ) are about the same size and laterally widened by flat protuberances (paranota). The body outline is closed, the abdomen ( abdomen ) attaches to the thorax without a step or constriction, so that an elongated teardrop-shaped spindle-shaped shape results, which is very uniform and hardly modified within the order.
The three pairs of legs sitting on the thorax have flattened, elongated hips (coxes) and thighs (femora). The foot ( tarsus ) consists of two or three segments (only five with tricholepidion ), three claws sit on the pretarsus, the middle one being slightly shorter. Fish have two pairs of thoracic and usually seven pairs of abdominal respiratory orifices ( stigmas ), in contrast to the Archaeognatha , the tracheal trunks of them are connected by cross connections (anastomoses).
The elongate, tapered rearwardly abdomen consists of eleven segments clearly visible and ends in two long attachments or "Raifen" ( cerci ) and a central Terminalfilum . These three tail threads are mechanical sensory organs that warn the animal of predators coming from behind . The belly plates (sternites) of the fish are partially reduced and only cover the middle of the abdomen. To the side of them are two larger plates, which emerge from the embryonic leg systems and are therefore called coxosternites. As further remnants of the abdominal extremities, attached to the coxosternites are single-unit, movable appendages called styli (also called “styluses”); these are sometimes located on segments two to nine, but always on the seventh to ninth segment. Inside (median) of the styli there are two small, evertable bubble-shaped vesicles, the coxal vesicles. These are pronounced on a different number of segments; there are none in the Lepismatidae family .
The entire body of the fish is usually covered with shiny scales, which often only appear in the course of ontogenesis , in the case of the silverfish, for example, after the third molt. These scales react to contact and accordingly represent mechanoreceptors . The families Nicoletiidae and Maindromiidae completely lack them.
Way of life
Fish are bottom-living, nocturnal insects of the tropics and subtropics. In Central Europe there is only one free species, the antfish ( Atelura formicaria ), which lives in nests of different ant species. A number of other species live in houses ( synanthropic ), these are now abducted worldwide. The most important synanthropic species worldwide are the silverfish ( Lepisma saccharina ) and the furnacefish ( Thermobia domestica ), which often live in warm rooms such as bakeries . For some time now, the combfish ( Ctenolepisma lineata ) has also been observed, especially in southern Germany. The paper fish ( Ctenolepisma longicaudata ) was first detected in northern Germany in 2007 . In 2017, the ghost fish ( Ctenolepisma calva ) , which had previously only been native to the tropics, was discovered in Chemnitz .
The animals feed on organic matter, mostly dead plant remains (saprophag), many Nicoletiidae are herbivores (phytophag), the three representatives of the very rare Maindromiidae family are probably predators (predators). The Nicoletiidae family lives in the ground or in litter, some species in caves and underground cavities. Almost all representatives of the Ateluridae and also a number of Lepismatidae are specialized inhabitants of ant and termite nests. They are tolerated as guests by the hosts there because they take on the respective nest odor, and as commensals they feed on food and prey remains, and occasionally also on body fluids. The other species live mainly on the soil surface. The specific biology of most species is little known. In some, including the oven fish, the digestion of cellulose by means of an endogenous enzyme (not made possible by symbiotic microorganisms) has been proven. The way of life of the synanthropic species, which can occasionally appear as pests, is better researched, although the damage caused is in most cases rather minor.
Fish mostly live in a relatively humid environment. However, some are adapted to dry habitats, including the synanthropic species that have to cope with the reduced humidity of heated apartments. Silverfish can tolerate drought up to a relative humidity of 75%, ovenfish even up to 50%. The ability to absorb water vapor or possibly contact water from the environment helps the animals to survive in a dry environment. The organ that absorbs moisture is the rectum.
Reproduction and life cycle
The little fish evolve directly from larvae that in physique and lifestyle of adults (Adulti or imagines are barely distinguishable) and regularly occur together with these. In contrast to winged insects (Pterygota), adults also continue to molt with them (both sexes, also during the reproductive period). These moults can take place very often and in quick succession, in the case of the oven fish about every ten days.
The transmission of the seeds for fertilization is indirect in the fish (that is, without mating). For this purpose, the male of the silverfish, for example, spins a thread web into a rectangular structure of the habitat and places the sperm packets on it when a female sees it in the vicinity. The female ingests these spermatophores when she walks under the net, guided by the male. The sperm in the fish are typically stored in twos to form double sperm, which are connected to one another at the front end and move together (“syzygy”). The connection dissolves in the female's seminal receptacle (receptaculum seminis). It then lays the eggs in small clutches, usually in cracks in the floor, using a short egg-laying device ( ovipositor ).
Only in the family Nicoletiidae does unisexual reproduction ( parthenogenesis ) occur in some species .
The approximately 470 species are divided into five families :
- Lepidotrichidae . The only species Tricholepidion gertschi has numerous plesiomorphic features. Some taxonomists suspect an isolated position without any close relationship to the other fish, so that this would possibly represent its own order . It lives in humid places on the North American Pacific coast. A related species has been described as a fossil from Baltic amber before the recent one .
- Maindromiidae , three species with a strikingly disjoint distribution, only in Asia Minor and South America (Chile).
- Lepismatidae , most species-rich family with over 200 species.
- Ateluridae . The Ateluridae are possibly an artificial grouping ( paraphyletic ).
Despite the presumed fundamental (basal) position in the system of insects, fossils, which with some certainty belong to the order, were not found before the Cretaceous . Almost all associated fossils are inclusions in amber. Such in limestone from the Cretaceous period are only found in the famous fossil site of Crato in Brazil.
- Dicondylia ( group )
- Shaggy tails (old classification)
- Bernhard Klausnitzer: Zygentoma, little fish. In: Westheide, Rieger (Hg): Special Zoology Part 1: Protozoa and invertebrates. Gustav Fischer Verlag, Stuttgart, Jena 1997; Page 627.
- ↑ Giant silverfish discovered in Portugal , orf.at, April 11, 2012
- ↑ Carsten Renker, Gerhard Weitmann, Ragnar Kinzelbach: Current state of knowledge on the distribution of the combfish - Ctenolepisma lineata (FABRICIUS, 1775) in Germany. In: Mainz Natural Science Archive 46/2008: 263–268.
- ^ Aliens among us - an encounter with the sixth species - Museum für Naturkunde Chemnitz. (No longer available online.) Archived from the original on April 11, 2017 ; Retrieved April 12, 2017 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ JAL Watson: Moulting and reproduction in the adult firebrat Thermobia domestica (Packard) (Thysanura, Lepismatidae). I. The moulting cycle and its control. In: Journal of Insect Physiology 10 (2) / 1964: 305-317.
- ↑ Veronica Dougherty Picchi: Parthenogenetic reproduction in the silverfish Nicoletia meinerti (Thysanura). In: Journal of the New York Entomological Society 80 (1) / 1972: 2-4.
- ^ Markus Koch: Toward a phylogenetic system of the Zygentoma. In: Klaus-Dieter Klass (Hg): Proceedings of the 1st Dresden Meeting on Insect Phylogeny: "Phylogenetic relationships wihin the insect orders" . In: Entomologische Abhandlungen 61 (2) / 2003: 122–125.
- ↑ David Grimaldi, Michael S. Engel: Evolution of the insects. Cambridge University Press (2005) ISBN 0521821495
- ^ David M. Martill, Günter Bechly, Robert F. Loveridge: The Crato Fossil Beds of Brazil: Window into an Ancient World. Cambridge University Press (2007). ISBN 0521858674