Psephenidae
| Psephenidae | ||||||||||||
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Eubria palustris |
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Psephenidae | ||||||||||||
| Lacordaire , 1854 |
The Psephenidae are a family of beetles. The beetles themselves have a very short lifespan and are rarely found near the banks of water. The larvae live in the water and are flow specialists. 263 species have been described worldwide, which are divided into 31 genera and five subfamilies. There is only one species in Europe, Eubria palustris , which also reaches Central Europe. The family is morphologically very diverse and has numerous special adaptations to its very extreme habitat. T. are very different.
features
They are small beetles with a body length between 1.1 and 8.5 millimeters. They are mostly inconspicuously brown in color, but there are some genera with conspicuous red or yellow warning signs . As a rule, they are short, oval and domed, but there are also elongated and somewhat flattened species. Usually they are quite softly sclerotized and finely and densely hairy. The head is mostly pulled back far into the trunk and in many species is not visible from above. The mouthparts point downwards (hypognath). The antennae have between 6 and 11 members, their shape is usually noticeably different between the sexes ( sexual dimorphism ). The antennae of the males are often toothed or comb-shaped, sometimes also thread-shaped, but extremely elongated (up to three times the body length). The mouthparts are more or less regressed, the mandibles are rudimentary or missing entirely. The palps of the maxilla and labium are well developed. Often the maxillary palps have special formations, they can be split or provided with special attachments. The pronotum (pronotum) is rounded on the sides, sometimes weakly toothed. The wing covers (elytra) are usually well developed, but in some genera they are strongly reduced, so that the abdomen and parts of the trunk are exposed. Mostly they are soft and flexible. In the subfamily Eubrianacinae they have dot stripes, in most Eubriinae they have roughening (microgranulation) in different patterns or scattered dots, otherwise they are smooth. The hind wings are usually well developed, the beetles are capable of flight. In some groups (e.g. Psephenoidinae) the vein has almost completely regressed. The tarsi are five-limbed, in the males some tarsal limbs are often expanded and the claws are split at the tip (two-pointed). Five sternites are visible on the abdomen, except in the subfamily Psepheninae. Here there are seven for the male and six for the female.
Larvae
The 4 to 11 millimeter long larvae are yellow or brown in color, often with markings. They are extremely flattened. The tergites have extensions called pleurites on the sides. These can be wider than the actual body. On the sides they usually have a hem of intricately shaped bristles. The roughly square head is hidden under a protrusion of the pronotum and cannot be seen from above. The result is a closed, almost circular body outline that resembles a flat disk or a suction cup. This has given the animals in America (where they are more common) the popular name "water pennies". (The first discoverer of the larvae, William de Kay, completely misunderstood the nature of these peculiarly transformed larvae and described them as a type of cancer.) The body shape is an adaptation to the special habitat of the larvae: the surface of stones in rapids and fast-flowing mountain streams. Exceptionally, there are also species with short, hook-shaped pleurites and elongated shapes; these live on dead wood (mostly narrow, dead branches).
On the head of the larvae are short, three-part antennae, the third part of which is extremely shortened. The mandibles are mostly flat and sickle-shaped and adapted to the particular way of life, they are used to scrape off the algae growth on stones. On the trunk sit three pairs of five-limbed legs with very strong claws to hold on to the stone surface. The abdomen consists of nine visible segments, the last often has a recess at the back or is in two parts.
The breathing of the psephenid larvae is remarkable because a number of different special adaptations are formed in the various subfamilies. As a result, almost all the possibilities that exist with the beetles as a whole are realized in a family. The Eubirianacinae and Psepheninae have z. B. open spiracles on the mesothorax and eight abdominal segments, in the Psephenoidinae all spiracles are closed. The Psephenoidinae and Eubriinae have a gill cover (operculum) on the ventral side of the ninth abdominal segment, including a breathing chamber with two retractable gills (similar to the "hook beetles", the related Dryopidae and Elmidae ). The Psepheninae and the Eubrianacinae have free, thread-like gills on the ventral side of the abdominal segments. Eubriinae and Psepheninae have a tuft of bristles at the end of the abdomen, which increases the surface of the stigma.
Dolls
The Psephenidae usually pupate in the water, in the larval habitat. Some groups leave the water to pupate, they then usually sit freely attached to the underside of stones or branches immediately above the water level. The pupation of the Psepheninae and the Eubrianacinae takes place in the larva’s habitat, hidden within the last larval skin (exuvia), which is cemented to the stone surface for this purpose. The pupae correspond to the larvae in terms of their coloration and cannot be easily distinguished from them. Like the larvae, the pupae have developed special organs for breathing underwater. The Eubrianacinae have gills on the seventh abdominal segment, which go back to reshaped spiracles. These are pushed out from the segmental membranes of the larval exuvia. The Psephenoidinae have gills on all abdominal segments. In the Psepheninae and Eubriinae normal, open stigmas are present, which in the Eubriinae sit on projections (tubercles).
Life cycle and way of life
The larvae of the Psephenidae live in water and are usually specialists in mountain streams with very fast currents. They can also colonize rapids, a habitat where few other species can follow. They mostly live on the surface of stones, where they graze on the organic growth of algae ( periphyton ). Few genera occur in weakly agitated water. Some specialize in submerged deadwood. As habitat specialists, you are sensitive to water pollution.
Most of the species whose life cycle has been studied more closely need one year (univoltin) for larval development. The North American Psephus herricki , and possibly other species, take two years to develop. At least in the tropics, there are also species with several generations per year.
The adults of the Psephenidae only live a short time. Their mouthparts have regressed and they do not ingest food. They are mostly nocturnal and during the day they sit hidden on the underside of leaves or in the litter, almost always next to water. Some species have become known through complicated mating games in which numerous individuals gather on stones moistened by spray. Others find their mating partners in flight. The life cycle with long-lived larvae and extremely short-lived adults was compared to that of mayflies . After mating, the female submerges in the water, where she lays clutches of 400 to 600 eggs, cemented to the surface of stones. It dies immediately afterwards, usually still under water. The eggs hatch after a development time of 12 to 15 days.
Systematics
The Psephenidae belong to a family group within the Byrrhoidea, which exclusively includes families with aquatic larvae, this group has been described as "Dryopoidea". The family's monophyly is well covered. The Psephenidae are divided into the following subfamilies:
The Afroeubriinae were only reorganized by Lee in 2003.
swell
- Chi-Feng Lee (2003): Phylogeny and taxonomy of Psephenidae (Coleoptera, Byrrhoidea). Diss., Chicago State University.
- Lee, C.-F., Jäch, MA & Beutel, RG: 18.7. Psephenidae Lacordaire, 1854, In: Rolf G. Beutel & Richard A. Leschen (Eds.) Handbook of zoology. Volume IV. Arthropoda: Insecta. Part 38. Coleoptera. Volume 1: Morphology and systematics, Archostemata, Adephaga, Myxophaga, Polyphaga partim. Berlin, New York: Walter de Gruyter. pp. 521-533.
- Willam Shepard (2011): Psephenidae. Water penny beetles. Version February 5, 2011 (under construction). [1] in The Tree of Life Web Project
Web links
Individual evidence
- ↑ Chi-Feng Lee (2003): Phylogeny and taxonomy of Psephenidae (Coleoptera, Byrrhoidea). Diss., Chicago State University.
- ↑ Harley P. Brown & Chad M. Murvosh (1974): A Revision of the Genus Psephenus (Water-Penny Beetles) of the United States and Canada (Coleoptera, Dryopoidea, Psephenidae). Transactions of the American Entomological Society Vol. 100, No. 3: 289-340.
- ↑ Chad M. Murvosh (1992): On the Occurrence of the Water Penny Beetle Eubrianax edwardsii in Lentic Ecosystems (Coleoptera: Psephenidae) The Coleopterists Bulletin Vol. 46, No. 1: 43-51
- ↑ Chad M. Murvosh (1971): Ecology of the Water Penny Beetle Psephenus herricki (DeKay). Ecological Monographs Vol. 41, No. 1: 79-96
- ↑ Chi-Feng Lee, Masakata Sato, William D. Shepard, Manfred A. Jäch (2007): Phylogeny of Psephenidae (Coleoptera: Byrrhoidea) based on larval, pupal and adult characters. Systematic Entomology 32: 502-538. doi : 10.1111 / j.1365-3113.2006.00374.x