Lecture 4: BASAL HEXAPODS
At least 5 major hexapod lineages originated prior to the appearance of winged hexapods. All hexapods share a common tagmosis pattern, resulting in 3 main body parts (head , thorax, abdomen), in addition to numerous other details of morphology and development. This and the total lack of evidence suggesting any hexapod lineage is closer to a non-hexapod lineage is strong evidence that the Hexapoda is monophyletic. The Insecta share a lack of muscles in the flagellum.
This phylogeny illustrates the basal divisions of the Hexapoda. Some authors accept the Diplura as sharing a common ancestor with Collembola and Protura, unlike in this figure. The Order Monura went extinct during the Permian.
This flow-chart should help you identify hexapods to one of the groups listed below.
INTRODUCTION: A small, ancient Hexapod lineage (considered a Class in some modern classifications) that had evolved prior to the evolutionary appearance of wings with only 48 species in America north of Mexico and about 400 described species known in the world.
RECOGNITION: Antennae absent, connical shaped head, fore leg pair modified for sensory purposes. Protura are pale, delicate, cryptic arthropods less than 2 mm (0.6-1.5mm) long that move slowly.
HABITATS: These organisms inhabit soil, humus, decaying vegetation, and rotting wood; they live under bark and are associated with fungus (thought to feed on mycorrhizal fungi).
COLLECTING: Due to their small size and secretive habits these organisms are rarely seen in the field (i.e. alive). They are most frequently found in soil and leaf litter extractions (e.g. Berlese Funnel Extraction). They are best preserved in 95% ETOH until they can be mounted on permanent slides.
TAXONOMY: Very little taxonomic research has been done on Protura of North America and there are few good (faunally complete) collections. There is no specialist currently in North America
Bernard, E. C. 1978. Class and Order Protura, pp/ 47-54. In Immature Insects, vol. 1, ed. F. W. Stehr. Dubuque, Iowa: Kendall/Hunt.
Nosek, J. 1978. Key and diagnosis of Protura genera of the world. Annotationes Zoologicae et Botanicae Bratislava 122:1-59.
Tuxen, S. L. 1964. The Protura, a revision of the species of the world with keys for determination. Paris, France: Herman.
Yin, W.-Y. 1983. Grouping the known genera of Protura under eight families with keys for determination. Contr. Shanghai Inst. Ent. 3:151-163 (in Chinese)
Yin, W.-Y. 1984. A new idea on phylogeny of Protura with approach to its origin and systematic position. Scientia sin. (B) 27:149-160.
INTRODUCTION: Springtails. Together with Protura and Diplura form the Entognatha, an ancient, basal hexapod lineage sharing entognathous mouthparts (mandibles, maxillae etc. located within a 'gnathal pouch'). Collembolan fossils from the Devonian (ca. 400 million years ago) are among the oldest known records of terrestrial animals . There are ca. 6000 described species worlwide and ca. 700 Nearctic species of Collembola, with an estimate from 1979 ranking 70-75% of the Nearctic fauna known (i.e. 30-25% of the species have not been recorded as occurring in North America). These organisms are virtually ubiquitous in terrestrial systems, ancient and thus, one of the more successful arthropod lineages.
RECOGNITION: Small to minute (most <6mm), wingless, entognathous mouthparts, legs basically 4-segmented, abdomen 6 or fewer segments, furca (or furcula) present ('tail' that allows 'springing"). Often leap when disturbed.
HABITATS: Collembolans inhabit soil and leaf litter, although some species move actively over the surfaces of bark and flowers in daylight (unlike Proturans and Diplurans). Collembolans are major components of terrestrial ecosystems (and particularly significant members of the soil communities), consitituting a significant proportion of the animal biomass and are thus frequently and easily found. Most species whose feedings habits have been studied consume micro-organisms associated with the rhizosphere (plant-root horizon of soil) or with decomposing organic matter. Some species can be found on the surfaces of lakes&ponds or snow fields (snow fleas).
COLLECTING: As with most cryptic soil organisms, Collembolans are most easily found via Berlese extraction of soil, leaf litter or bark. Rarely they are taken in aquatic samples (from the water surface), or collected by hand (aspirator) from the substrate. Living Collembolans should be placed in 95% ETOH with 1% Glycerin. Pitfall traps also capture many Collembola.
TAXONOMY: There are two major lineages within Collembola that you can learn to recognize. The Arthropleona which are elongate (above figure, left) with 6 visible abdominal segments, and the Symphypleona, which have globular or oval bodies and whose individual abdominal segments are not discernible (above figure, right). Phase-contrast microscopy of slide-mounted specimens is usually necessary to identify species. See Snider (1987) for details on preparing slide-mounts.
Christiansen, K. A. and P. F. Bellinger. 1980-81. The Collembola of North America north of the Rio Grande. Grinnell, Ia.:Grinnell College. 1322 pp. (4 parts)
Maynard, E. A. 1951. The Collembola of New York State. New York, New York: Comstock Publishing Co.
Richards, W. R. 1968. Generic classification, evolution and biogeography of the Sminthuridae of the world (Collembola). Memoirs of the Entomological Society of Canada 53:1-54.
Salmon, J. T. 1964. An index to the Collembola. Bulletin Royal Society of New Zealand. Zoological Series 1:1-144, 2:1-644.
Snider, R. J. 1987. Class and Order Collembola, pp. 55-64 In Immature Insects, vol. 1, ed. F. W. Stehr. Dubuque, Iowa: Kendall/Hunt.
INTRODUCTION: A hexapod lineage closely related to the Protura and as ancient (evolved prior to the origin of wings). 64 species are known from North America in 4 families (two of which are known only from California) with about 800 species described for the world.
RECOGNITION: Pale in color, eyes absent, with two caudal (tail-like) appendages (some resembling earwig-like pincers) or filaments, generally <7mm in length.
HABITATS: Damp soil, under bark, under stones or logs, in rotting wood, in caves. Some detrivorous, herbivorous and carnivorous species groups.
COLLECTING: Like Proturans, these organisms are most frequently found via Berlese Litter extraction or flotation techniques. Pitfall traps occasionally capture Diplurans. Stored permanently in small vials of 70% ETOH.
TAXONOMY: There are three major lineages (often treated as families) that are easily discernible. Japygidae have forcepslike cerci (like an earwig's cerci), Projapygidae have stout, short & rigid cerci (1 species in USA), Campodeidae have elongate, flexible cerci. Very little taxonomic work as been done on the North American fauna and Diplurans are absent to rare in most collections.
Palct, J. 1957. Diplura. Genera Insectorum. Fascicule 212: 213 pp.
Smith, L. M. 1960. The family Projapygidae and Anajapygidae (Diplura) in North America. Annals of the Entomological Society of America, 53: 575-583.
Smith, L. M. and C. L. Bolton. 1964. Japygidae of North America, 9. The genus Metajapyx. Journal of the Kansas Entomological Society 37: 126-138.
INTRODUCTION: Jumping Bristletails. One of the two extant, apterygote (wingless) true Insect lineages. 350 species (some extinct) worldwide and ca. 20-35 in North America. It is estimated that only 60% of the North American fauna is documented.
RECOGNITION: Can be differentiated from Thysanura (Zygentoma), which look quite similar, by their contiguous (touching) eyes. Primitively wingless, arched thorax, with the ability to jump, elongate antennae, cerci and a median caudal filament.
HABITATS: Microcoryphians are found in leaf litter, under bark, among rocks along the seashore or in old stone walls. They feed on a wide variety of decaying organic matter, particularly plant remains, on lichens and terrestrial algae.
COLLECTING: Most species are nocturnal or crepuscular and can be found actively moving over surfaces only at night. During the day they can be found in crevices in bark and among stones, or in leaf litter. Specimens should be stored permanently in 70% ETOH.
TAXONOMY: There are two families that are easily distinguishible: Machilidae, which has scales on the base of the antennae and legs (14 spp. in North America), and the Meinertellidae, which lacks scales (6 spp. in N. America). Meinertellids are more commonly found.
Wygodzinsky, P. and K. Schmidt. 1980. Survey of the Microcorphyia (Insecta) of the north-eastern United States and adjacent provinces of Canada. American Museum Novitates No. 2701: 17pp.
INTRODUCTION: Silverfish, Bristletails, Firebrats. The second of two major, extant lineages of true Insects that orginated prior to the appearance of wings. There are about 30 species in North America with about 370 species in the world. Like the Microcoryphia, it is estimated that only about 60% of the North American fauna is documented.
RECOGNITION: Like the Microcoryphia, Thysanurans are primitively wingless, elongate-bodied, somewhat more flattened than Microcoryphians, with three tail-like appendages at the posterior end of the abdomen. Often entirely covered with scales (that drop off when handled). The eyes are much smaller than Microcoryphian eyes and do not touch.
HABITATS: Thysanurans occur in a variety of habitats, a few species are anthrophilous ("human-loving") and live in houses feeding on starches of foods and pastes, some live within ant nests or termite nests and some species are cave endemics. They can be found under stones, bark and in leaf litter and they generally feed on vegetation. All species are nocturnal and secretive. They do not jump like Microcorphians but Thysanurans can run quite fast.
COLLECTING: House frequenting species are the most often encountered but it is very difficult to capture Thysanurans without damaging them. Thysanurans are too soft-bodied and delicate to pin and dry but due to their scales, which float off in liquid, they do not preserve well in ETOH either. Wild species can be found in Berlese extractions and pitfall traps.
TAXONOMY: In New England we have only species of the family Lepismatidae.
Remington, C. L. 1954. The suprageneric classification of the order Thysanura (Insecta). Annals of the Entomological Society of America, 47:621-627.
Wygodzinsky, P. 1961. A review of the silverfish (Lepismatidae, Thysanura) of the United States and Caribbean area. American Museum Novitates, No. 2481: 26 pp.