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Collembola Introduction • Springtail跳虫 have the widest distribution of any hexapod group, occuring throughout the world, including Antarctica南极. They are probably the most abundant hexapods on Earth, with up to 250,000,000 individuals per square acre英亩. They are found in soil, leaf litter, logs木, dung粪, cave洞穴, shorelines海岸线, etc. There are about 6000 known species. • Devonian-Recent泥盆纪. Oldest fossil化石 is of Rhyniella praecursor Hirst and Maulik from the Middle Devonian 中 泥盆世of Scotland. • The name “Collembola” is derived from “Colle” = glue and “embolon” = piston or peg. This refers to the belief that the ventral腹部 tube has adhesive properties粘着性, that is, that it is a “glue-peg”. However, the tube‘s function is primarily for excretion排泄 and maintaining 供 养water balance. Characteristics Among the prominent derivedcharacteristics of this group are: •Ventral腹部 tube (“collophore”) on segment 1 of abdomen (adhesive带粘性的 in some groups, but primarily involved with excretion and water transport) •springing mechanism formed from retinaculum翅 缰沟 on segment 3, furcula弹器 on segment 4 •4-segmented antennae (segments sometimes subsegmented, giving the appearance of more than 4 segments) •6 abdominal segments Characteristics Other characteristics include ： • indirect 间接的sperm transfer with globular球 状的 stalked spermatophore 精囊 • Some Neanuridae have polytene chromosomes多线染色体的 • Adults continue moulting throughout life (up to 50 moults) • Reproductive生殖的再生的 instars alternate with feeding instars • Cerci lacking Life History & Ecology: The springtails are among the most abundant of all soil-dwelling arthropods节肢 动物. They live in a variety of habitats where they feed as scavengers洞穴 on decaying vegetation and soil fungi. Most species are small (less than 6 mm in length) and quite susceptible易受影响的 to desiccation 干燥unless they remain in a moist environment. A unique, tube-like structure, the collophore粘管 is located ventrally on the first abdominal segment of most species. The exact function of this organ is unknown, but it probably helps maintain water balance by absorbing moisture from the environment. Springtails are named for a forked 叉状的jumping organ (the furcula) found on the fourth abdominal segment. The furcula is retracted against the ventral wall of the abdomen and held there, in cocked position, by a special catch (the tenaculum) on the third abdominal segment. Releasing the tenaculum causes the furcula to snap down against the substrate and flip the organism some distance through the air. This device, present in all but a few genera, seems to be an effective adaptation for avoiding predation. Immature collembola are similar in appearance to adults. They usually molt 4-5 times before reaching sexual maturity, and continue to molt periodically throughout the rest of their life. Unlike most other arthropods, springtails appear to have evolved in a cool climate. Their relative abundance in the soil tends to increase as the mean annual temperature decreases and their development is most rapid under cool, humid conditions. Major Families: • Hypogastruridae -- the largest family in the order. These are small, plump hexapods that may lack compound eyes or a springtail (furcula). Includes the snowflea, Hypogastrura nivicola. • Isotomidae -- second largest family in the order. These hexapods are elongate and lack scales on the upper surface of the body. • Entomobryidae -- common soil-dwellers. The fourth abdominal segment is significantly longer than the others. • Sminthuridae -- body globular in shape. The family includes the garden springtail (Bourletiella hortensis) which occasionally damages plant seedlings.