Collembola (Springtails, Collembolans)
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chapter 6 Collembola (springtails, collembolans) Arne Fjellberg The Collembola (springtails) are one of the dominant ani- three thoracic segments bears a leg consisting of claw, mal groups in most soil ecosystems including those of the tibiotarsus, femur, trochanter, coxa and subcoxa. Some of arctic regions. Their unique body design with the low the six abdominal segments have structures derived from number of abdominal segments render them immedi- paired appendages: Ventral tube on the first segment, ately recognizable among the antennate hexapod arthro- retinaculum on the third, and furca (the jumping organ) pods. Their exact phylogenetic relationships to other on the fourth. Genital organs open on the fifth and anus arthropods are currently a subject of much discussion, see on the sixth (terminal) segment. The genital aperture of chapter 2. the female is a transverse slit with an anterior and a poste- rior lip, the male aperture is a roundish papilla with an incision from behind Fig.1 shows the general morphology Morphology of the Greenland species Hypogastrura concolor. For a more detailed description Fjellberg (1998) may be Collembola are enthognathous hexapod arthropods, i.e., consulted. their mandibles and maxillae are enclosed in the head Abbreviations used in the text (see also Fig.1). a: Anterior; capsule. Most species are 0.5–1.5 mm long, with some spe- A: Apical setae of tibiotarsus; abd.: Abdomen (abd.1: First cies reaching more than 3 mm.The antennae are 4–seg- abdominal segment); ant: Antenna (ant.1: First antennal mented, the eye-field has 8 socalled ‘ocelli’ (dispersed segment); cl: Claw; m: Median; M: Macrochaeta; ms: compound eye ommatidia, hence non-homologous with Spine-like microsensillum; p: Posterior; PAO: Post anten- insect ocelli) which often become reduced. Each of the nal organ; s: Sensillum; T: Accessorial seta of the apical Figure 1 General morphology, Hypogastrura concolor. 6. Collembola (springtails, collembolans) – Fjellberg 49 whorl on tibiotarsus; th: Thorax (th.1: First thoracic seg- 2. Th.1 large, with some dorsal setae. Mostly short ment); tib: Tibiotarsus and thick species with short extremities. Many spe- cies completely white, these have no furca but usually a pair of anal spines present on tip of Reproduction and development abdomen (except Anurida/Micranurida; section Poduromorpha) .....................................3 Both sexual and parthenogenetic reproduction are com- – Th.1 reduced, dorsal setae absent. Generally well pig- mon in Collembola. Some species may switch between mented, elongate forms with long extremities. The the modes, depending on environmental conditions. few white species have furca present (except Pseu- The juvenile hatch from the egg with all body segments danurophorus), but anal spines absent (section developed. Several instars separated by moults are passed Entomobryomorpha) ................................5 before the adult appears. Under arctic conditions the life 3. Body pigmented or white. None of the white span may cover several years and maturity is not reached species have pseudocelli on the body or finger-like until at least two years age in some species. Sperm transfer papillae in the ant.3 organ ..........................4 is indirect, with males setting off spermatophores on the – All species white with pseudocelli on the body. substrate. These are picked up by the females, somtimes The larger species (>1.0 mm) also with finger-like after a complex courtship (Goloshchapova et al. 2005). papillae in the ant.3 organ (Fig. 2A) . Onychiuridae, p. 57 4. Mandibles strong, with distinct molar plate Collecting and identification (Fig. 1). Tip of abdomen with 2 anal spines (absent in Willemia denisi) ...........Hypogastruridae, p. 50 Collembola inhabit a most diverse assemblage of terrestrial – Mandibles reduced, no molar plate. Anal spines biotopes from coastal seashores to inland nunataks. Mass either absent or 3 or 5 (Figs 7A, B) ................... occurrences may be observed in littoral wrack beds or other . Neanuridae, p. 55 accumulations of rich organic substrate, at shore of lakes or 5. Body with an open cover of simple hairs only. on melt water at snow thaw in spring. Specimens are easily PAO present (except in the white, blind Isotomiella collected by hand into a vial with 80% ethanol, but more minor) ..............................Isotomidae, p. 63 efficient is extraction of soil/litter samples placed on a fine – Body with scales or a dense cover of ciliated, apically wire mesh in a funnel which is heated from above by an expanded macrochaetae (Figs 2B, C). PAO absent, electrical light bulb. Animals will move away from the heat eyes and pigment present in the two Greenland spe- and finally fall through the mesh into a collecting vial cies .............................Entomobryidae, p. 76 placed under the funnel. Samples of specimens collected 6. Larger species, eyes present, antennae longer than directly in alcohol should be heated on a water bath until head (suborder Symphypleona) ....................7 boiling, to ensure proper preservation of the material. – Very small (0.5 mm), blind species with With some training a number of species will be recog- antennae shorter than head ( suborder Neelipleona, nised at low magnification while floating in alcohol, or Fig. 19A) ...............................Neelidae, p. 76 even by eye in the field. Smaller species always need to be 7. Head with 8+8 ocelli, darker species . .8 mounted in slides and examined by a microscope. – Head with 1+1 ocelli, pigmentation weak or absent Specimens may be cleared for microscopy by heating in a (Fig. 19B) ........................Arrhopalitidae, p. 77 mixture of glycerol and lactic acid (concentrated) in pro- 8. Males with simple antennae, females with a pair of portions 1:3. Small juveniles may not always be safely modified setae below anus (Fig. 2H). Tibiotarsal identified by the following keys. organ absent .........................................9 – Males with modified antennae (Fig. 2D), females without modified setae below anus. Tibiotarsal Key to families organ present (Fig. 19G) ...... Sminthurididae, p. 77 9. Ant.4 subdivided (Fig. 2G) .........................10 1. Body elongate, clearly segmented (suborder – Ant.4 simple ......................Katiannidae, p. 78 Arthropleona, Fig. 1) . 2 10. Tibiotarsi with simple apical hairs (Fig. 2F) ......... – Body more or less globular, segments of thorax and ................................... Sminthuridae, p. 80 abdomen fused (suborders Neelipleona and Sym- – Tibiotarsi with clavate apical hairs (Fig. 2E) ���������������� phypleona, Figs 19, 20, 21) ...........................6 .................................. Bourletiellidae, p. 79.