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Keys and Bibliography to the Collembola

Keys to the Genera of the Collembola

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Keys to the Genera of the Collembola

In using these keys the bracketed number following each generic name refers to the entry in the bibliography in which the original generic description may be found. Only new synonymy is discussed in the footnotes, as space does not permit of a discussion of all the synonymy included in this work. Most of the synonymy indicated is accepted by specialists in this field of entomology, but, where there may be some doubt, a second bracketed number has been included to indicate works in which discussion may be found.

In working out the keys, the affirmative or the normal condition always takes precedence over the negative or abnormal condition, and is worked out to its conclusion first.

There has, in the past, been a certain amount of confusion in the interpretation of the furcula and the clothing among the Collembolan specialists. These structures are interpreted in these keys as defined below, and I suggest that the adoption of these definitions in future work may help to clarify this situation.

Furcula: This organ is described extended at right-angles from the body, in a similar position to that adopted by the legs in repose, so that it presents an anterior and a posterior face. The anterior face is the surface usually described as dorsal when the organ is held in the resting position beneath the abdomen.

Clothing: The clothing of Collembola is extremely important in their systematic study, and may consist of scales, setae, spines, bristles, and hairs, all of which may or may not occur together on the one species.

Scales, when present, may be either hyaline or pigmented; plain, ribbed, fluted, striated, or ciliated, and of various shapes from round and blunt to oval or pointed.

Setae are the most common form of clothing occurring in the Collembola, Several distinct types of setae in addition to the normal plain setae can be recognized and defined as follows:—

  • Ciliated setae, in which the shaft of the seta is supplied with whorls of fine hairs.
  • Serrated setae, in which the shaft of the seta is, as its name implies, serrated or supplied with well-spaced tooth-like structures.
  • Flexed setae, in which the shaft of the seta is ciliated and bent over towards its apex, which is more or less flattened, and bears longer ciliations than does the shaft.
  • Pubescent setae, in which the shaft of the seta is densely clothed with short, even hairs, giving it the appearance rather of a squirrel's tail.
  • Clavate or spathulate setae, in which the apex is swollen into a knob or expanded into a spathulate form. The knob is sometimes divided.

Setae are readily recognized and differentiated from hairs and bristles in that they taper gradually from the base towards the apex, where they terminate in a fine point.

Hairs may be recognized by their even width for almost their entire length and by their flexible nature. Hairs in Collembola may be long or short, plain, ciliated, clavate, or spathulate. The hairs occurring at the apex of the tibio-tarsus, in association with the claw, though in structure more often of the tapering nature of setae, are referred to as tenent hairs and are generally either clavate or spathulate.

Bristles are really stout, stiff hairs. They may be plain, ciliated, or divided. Divided bristles are those in which the apex is subdivided into from three to seven short finger-like processes. This type of bristle is usually, situated at the apex of the mesotergum, and is characteristic of the Lepidophorellinae.

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Spines commonly occur on the dentes, but sometimes also on the tibio-tarsi or on the body, and in certain genera of Symphypleona on top of the head. They may be plain, serrated, or ciliated, and either straight or curved.

Lasiotrichia is a new name I am proposing to differentiate the long, thin, wavy, ciliated sensory hairs from the similar but non-ciliated wavy hairs or bothriotrichia. Bothriotrichia always arise from small cups or mounds on the cuticle, whereas lasiotrichia generally arise direct from the cuticle as do ordinary setae and hairs.

Tricobothria are small sensory cups, domes, or swellings which occur commonly among the Symphypleona. They are situated on the sides of the body and generally give rise to bothriotrichia or short, stiff sensory bristles.

Key to the Sub-Orders, Families, Sub-Families, and Tribes of the Order Collembola
1. Trachea present, spiracular opening on posterior ventro-lateral portion of head Sub-order Symphypleona Börner
(Page 28)
Trachea absent; body elongate; segmentation distinct, the abdominal segments generally separated Sub-order Arthropleona Börner
(Page 7)
2. Body somewhat elongate; head hypognathous; Abd. III reduced, Abds. IV–VI fused; furcal segment with a pair of strong ridges Family Actaletidae Wahlgren
(Page 28)
Body not elongate but distinctly globular; Abds. I–IV fused, Abds. V–VI usually demarcated from rest of body 28
3. All segments essentially similar; prothorax dorsally with setae, distinct and never hidden below mesotergum; stales absent; antennae short, with 3–4 segments; cuticle generally granulate or tuberculate; anal spines and pseudocelli often present; postantennal organ generally present Super-family Poduroidea Womersley
(Page 7)
Body segments usually dissimilar; prothorax without setae dorsally and usually reduced and hidden under mesotergum; antennae normally long with 4–6 segments; cuticle smooth; scales present or absent; postantennal organ present in Isotominae, absent in other sub-families Super-family Mydonioidea Salmon
(Page 17)
4. Head obliquely prognathous; ocelli; when present, situated on front half of head; postantennal organ usually present; furcula present or absent, when present usually short and straight, seldom reaching forward as far as ventral tube; dentes not annulated, without articulating apophyses with manubrium Family Hypogastruridae Börner
(Page 7)
Head hypognathous; ocelli, when present, situated on posterior half of head; postantennal organ absent; furcula reaching forward beyond ventral tube; dentes bowed horizontally, annulated distally, and with articulating apophyses with manubrium. Family Poduridae Börner
(Page 7)
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5. Body normally with pseudocelli; Ant III with complicated sense organ consisting of sense rods, sense clubs, papillae, and guard setae: ocelli absent; postantennal organ always present 5
Body without pseudocelli; sensory organ of Ant III simple, having sense rods but neither sense clubs nor papillae and seldom with guard setae; both ocelli and postantennal organ present or absent 7
6. Sense organ of Ant. III with the two sense clubs bent towards each other and often with an accessory lateral club, without papillae: unguiculus present but generally reduced and with or without terminal bristle Sub-family Tullberginae Bagnall
(Page 8)
Sense organ of Ant. III with the two sense clubs straight, without lateral accessory club, but with papillae; unguiculus present and well developed Sub-family Onychiurinae Börner
(Page 9)
7. Mandibles with well-defined molar area; maxillae normal Sub-family Hypogastrurinae Börner
(Page 10)
Mandibles without molar area, or entirely absent Sub-family Neanurinae Börner
(Page 12)
8. Body of normal shape sparsely clothed with smooth setae and occasional serrated or clavate setae Tribe Brachystomellini nov.
(Page 12)
Body of abnormal shape, either plump or noticeably widened 9
9. Body plump; posterior portion of head swollen, often with folds; pleural areas of body not swollen and separated off as paratergites Tribe Anuridini nov.
(Page 13)
Body widened and usually noticeably flattened, sometimes half as wide as long 10
10. Abd. VI large and bilobed; integument tuberculate; body segments usually with large bosses Tribe Neanurini Börner
(Page 14)
Abd. VI either wholly or partly hidden beneath Abd. V or partly enclosed by Abd. V; pleural areas of body often more or less swollen and separated off as paratergites Tribe Pseudachorutini Börner
(Page 15)
11. With either well-developed visible maxillary palpi or with well-developed cerci and long spines on Abds. V and VI 12
Without either visible palpi or cerci as above 13
12. With long three segmented maxillary palpi Family Palpigeridae Olfers (Fossil Collembola)
(Page 17)
With long cerci and spines on Abds. V and VI Family Catastylidae Olfers (Fossil Collembola)
(Page 17)
13. Abds. V and VI reduced; antennae long 4–6 segmented 14
Abds. V and VI not reduced; antennae short and stout, four segmented Family Protentomobryidae Folsom (Fossil Collembola)
(Page 22)
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14. *Trochanteral organ present; inner edge of claw generally with basal groove; Abd. IV generally longer than Abd. III; furcula present; scales present or absent; scales and setae often ciliated Family Mydoniidae Salmon
(Page 23)
Trochanteral organ absent; inner edge of claw without basal groove; Abd. III and Abd. IV generally subequal or Abd. III a little longer 15
15. Abd. III and Abd. IV approximately equal in length; Abd. IV sometimes a little longer; postantennal organ generally present; scales and lasiotrichia present or absent; furcula present 16
Abd. III longer than Abd. IV (rarely Abd. IV a little longer than Abd. III); scales present or absent, but if present then with longitudinal striae; postantennal organ absent; furcula present Family Tomoceridae Schaeffer
(Page 22)
16. Scales present; postantennal organ present; mucro long, with numerous teeth Family Oncopoduridae Bonet
(Page 17)
Scales absent; postantennal organ present or absent; mucro short Family Isotomidae
(Page 17)
17. Furcula present; Abds. V–VI either distinctly separated or fused 18
Furcula sometimes absent; when present, reduced, short, with mucrodens joint often indistinct; dentes never crenulate; Abd. VI reduced, sometimes hidden below Abd. V so that anus becomes more or less ventral; clothing of simple setae, serrated or ciliated setae absent Sub-family Anurophorinae Börner
(Page 17)
18. Furcula short, well developed, all joints distinct, manubrium usually longer than dentes; Abds. IV–VI or V–VI often fused; clothing of simple setae and, occasionally, longer serrated setae Sub-family Proisotominae Stach
(Page 18)
Furcula longer, well developed, all joints distinct; dentes longer than manubrium, slender, with posterior face crenulate and anterior face with many setae; Abds. V–VI sometimes fused; clothing of simple or serrated setae Sub-family Isotominae Schaeffer
(Page 19)
19. Dentes at least indistinctly annulated and corrugated, but not segmented; mucro small and without setae; Ant III not very much longer than Ant. IV Sub-fam. Lepidophorellinae Börner
(Page 22)
Dentes not or only very slightly annulated and corrugated, usually 2-segmented and always spined; mucro long with setae Sub-family Tomocerinae Salmon
(Page 22)
21. Scales present and distinctly ribbed, though sometimes tending to hyaline; mucro falciform; dentes spined and generally with spine-like scales; unguiculus simple; antennae not annulated Tribe Lepidophorellini Womersley
(Page 22)
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Scales absent; mucro toothed; Ants. III and IV and distal part of Ant. II annulated; dentes without spines Tribe Neophorellini Womersley
(Page 22)
22. Ocelli eight to each side; Ant III shorter than Ant. IV, not annulated; dentes lightly annulated and corrugated Tribe Novacerini Salmon
(Page 22)
Ocelli less than eight to each side 23
23. Ocelli six on each side; Ant. III much longer than Ant. IV; Ants. III and IV generally annulated Tribe Tomocerini Salmon
(Page 22)
Ocelli four to each side; Ant III only a little longer than Ant IV; both Ants. III and IV annulated Tribe Paratomocerini Salmon
(Page 22)
24. Dentes long and slender, prominently annulated and corrugated; mucro small Sub-family Mydoniinae Salmon
(Page 23)
Dentes neither annulated nor corrugated, long but not or only slightly tapering 26
25. Antennae with four segments Tribe Mydoniini Salmon
(Page 23)
Antennae with five or fix segments, I or II or both being subdivided; if only 4-segmented, then IV as long as body Tribe Orchessellini Börner
(Page 25)
26. Dentes with ciliated or fringed scales as welt as setae or spines; unguiculus with three-winged edge or reduced; scales present on body: ocelli absent Sub-family Cyphoderinae Börner
(Page 27)
Dentes without ciliated or fringed scales, but with setae and with or without spines; unguiculus with four-winged edge; mucro plump and generally indistinctly separated from dens; body with or without scales; ocelli present Sub-family Paronellinae Börner
(Page 26)
27. Each dens with 1–2 rows of ciliated spines along posterior face; dens many times longer than mucro; mucro short Tribe Troglopedetini Börner
(Page 27)
Dens without spines, but each dens with two rows of ciliated scales; mucro long and slender, with apical and usually ventral teeth Tribe Cyphoderini Börner
(Page 27)
28. Antennae arising from, or in front of, middle of head, four-segmented, and always very much shorter than head; head without elevated vertex; coxae of legs elongated and on outer side longer than trochanter; ocelli and postantennal organ absent; body with or without papillae; tenaculum without bristles; furcula present; bothriotrichia absent; very small species seldom more than 0.25 mm. long Family Neelidae Folsom
(Page 28)
Antennae inserted behind middle of head, four-segmented, sometimes with subdivided segments, and generally much longer than head; head with distinctly elevated vertex; coxae not elongated; on outer side much shorter than trochanter; tenaculum usually with bristles; bothriotrichia present Family Sminthuridae Lubbock
(Page 28)
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29. Vesicles of ventral tube with smooth walls; cuticle of body granular; tenaculum with lateral appendages at base of rami; traces of thoracic segmentation present Sub-family Sminthuridinae Börner
(Page 28)
Vesicles of ventral tube with tuberculate or "warted" walls; traces of thoracic segmentation absent 31
30. Anal and genital segments fused and bearing two sensory setae on each side Tribe Sminthuridini Börner
(Page 28)
Anal and genital segments separated, sometimes the latter fused with the furcal segment; genital segment bearing one sensory seta only to each side Tribe Katiannini Börner
(Page 29)
31. Antennae bent between segments II and III; Ant IV shorter than Ant III; furcal segment bearing large dorsal papilla and three pairs of sensory setae; tenaculum with basal appendages Sub-family Dicyrtominae Börner
(Page 30)
Antennae bent between segments III and IV; Ant IV longer than Ant III; tenaculum without lateral appendages; furcal segment without dorsal papilla Sub-family Sminthurinae Börner
(Page 30)
32. Clavate tenent hairs present, 2–3, appressed; unguiculus present or absent Tribe Bourlettiellini Börner
(Page 30)
Clavate tenent hairs generally absent; if present, then separated and outstanding; claw sometimes with tunica or sheath; unguiculus always present Tribe Sminthurini Börner
(Page 30)

* The trochanteral organ consists of a small area of specialized setae, hairs, or spines situated on the trochanter of each hind leg. Often it is a difficult character to see.