Diplura (Diplurans)

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Diplura

(Diplurans)

Class Entognatha

Order Diplura

Number of families 9

Evolution and systematics

Diplura is one of three orders grouped in the Entognatha, a lineage of six-legged arthropods separate from the true insects. The Entognatha share a common ancestor with true insects, but developed along their own distinct evolutionary path. Diplura means "two tails," and classified within the order are all Entognatha with paired tail appendages. This definition is rather superficial, and possibly delimits an artificial group. Multiple evolutionary units may be present within the order as currently defined, and new orders may eventually be created to separate them.

The fossil record of Diplura is sparse, owing to their soft-bodied nature. The oldest fossil commonly referred to this order lived in the Upper Carboniferous. Presently, the order contains approximately 800 species grouped into three suborders and nine families.

Physical characteristics

Diplurans are long and slender, cylindrical or dorsoventrally flattened in cross-section, 0.12–1.97 in (3–50 mm) in length. Body color is normally white or pale yellow, and the cuticle is often semitransparent. Wings are absent in all stages of development. The body is usually covered with hairlike structures called setae, infrequently with scales. The head bears no eyes, but supports a pair of long antennae bristling with complex sensory hairs. Each antennal segment contains its own musculature (a primitive feature), and some families possess unique telescoping antennae. Diplurans have chewing mouthparts concealed within a pouch formed by the front of the head, the defining feature of the Entognatha. The mandibles have one point of articulation with the head, another primitive, ancestral character.

The abdomen has ten segments. A pair of tail appendages, called cerci, is located on the last abdominal segment, and takes several forms in the various families. Cerci are either long and multisegmented, as in the family Campodeidae, or forcepslike, as in the family Japygidae. Pairs of small leglike structures called styli are present on the underside of most abdominal segments, and these act to support the long abdomen. Pairs of eversible sacs are also found on the underside of the abdomen, and these most likely function to maintain water balance.

Distribution

The order Diplura is widely distributed throughout the world, although a few families have restricted distributions.

Habitat

Diplurans are a component of the soil fauna. On the surface, they can be found in moist microhabitats, such as under rocks, logs, leaf litter, and tree bark. Some species live part or all of their lives within caves.

Behavior

Many methods of burrowing are found within the order. Members of the family Campodeidae prefer loose soil, burrowing with wormlike movements of their streamlined bodies. Campodeids are also capable runners on the surface. Species in the family Japygidae push into preexisting soil cavities with their strong legs, which are useless for running. Burrowing is aided by the mouthparts, and by telescoping antennae in species that have them.

Species with long, flexible tail appendages disengage them readily if grasped by a predator, allowing the rest of the animal to escape. Species with the tail appendages modified into forceps use them effectively for defense. Several accounts describe forceps being used to capture prey, but this is not believed to be their primary use.

Feeding ecology and diet

Diplurans feed on live prey, dead soil animals, fungi, living plants, and decaying vegetation. Most species are omnivorous, combining several food sources. Diplurans locate prey with their antennae; they stalk to attain striking distance, and rush to capture it. Prey items include small, soft-bodied mites,

worms, myriapods, and various adult insects and insect larvae, including smaller diplurans.

Reproductive biology

Male diplurans attach stalked sperm packets to the soil at random. Females with mature eggs search for these sperm packets and collect them with the genital opening. The eggs are also laid on stalks, and are placed in small clutches in leaf litter or in soil cavities. Parental care exists in several families, involving the female parent curling around her egg clutches, and remaining with the first and second instar larvae until they are capable of surviving independently.

The first two instars are prelarval stages, incompletely developed and incapable of feeding. Third instar larvae attain the typical adult form. Diplurans gradually increase in size and attain more setae with successive molts. No distinct change marks sexual maturity, the only indication being a full complement of body setae. Adults continue to molt, enabling regeneration of broken appendages. Up to 30 molts have been recorded, and lifespan may exceed two years.

Conservation status

No species of Diplura is listed by the IUCN, but populations of Diplura are little known. There are a large number of endemic species in the order with very restricted distributions, and habitat destruction could easily threaten these more locally distributed species. Some species appear to be coping well with the presence of man; for example, considerable diversity has been recorded in urban areas such as Vienna, Austria.

Significance to humans

A few species are known to cause minor damage to garden vegetables. Most do not affect humans in any way.

Species accounts

List of Species

Campodea fragilis
Heterojapyx gallardi
Holjapyx diversiunguis

No common name

Campodea fragilis

family

Campodeidae

taxonomy

Campodea fragilis Meinert, 1865, Copenhagen, Denmark.

other common names

None known.

physical characteristics

Length 0.12–0.19 in (3–5 mm). Body thin, flexible, translucent white to pale yellow. Tail appendages multisegmented, long, and antennalike. Legs and abdominal styli well developed. Precise identification of this species requires examination of the setae.

distribution

All continents except Antarctica.

habitat

Damp, loamy soil.

behavior

Gregarious; retreats from light when exposed.

feeding ecology and diet

Feeds on plant matter and dead insects.

reproductive biology

Males produce large numbers of sperm packets, as many as 200 per week. Females lay eggs within natural soil spaces, avoiding direct contact between eggs and soil. Eggs hatch in 12–13 days.

conservation status

Not threatened.

significance to humans

None known.

No common name

Heterojapyx gallardi

family

Heterojapygidae

taxonomy

Heterojapyx gallardi Tillyard, 1924, Epping, New South Wales, Australia.

other common names

None known.

physical characteristics

Length 1.2–2 in (30–50 mm); a giant of the order. Females larger than males. Body mostly white. Abdominal segment eight tinged with light brown, segments 9, 10, and forceps dark brown and shiny. Forceps have asymmetrically serrated inner margins.

distribution

Coastal mountains of New South Wales, Australia, in the vicinity of Sydney.

habitat

Lives in soil. Found under large rocks and logs when on the surface.

behavior

Burrows to depths below 18 in (45 cm). Found deeper during dry weather, emerging onto the surface when the soil is wet. Antennae continually scan the surroundings while on the surface.

feeding ecology and diet

Predaceous. Waits just below the surface of the soil with forceps exposed to capture prey. Once prey is grasped, it is pulled beneath the soil and fed upon.

reproductive biology

Females apparently offer parental care, having been observed with early instar larvae. Females probably guard their eggs as well.

conservation status

Not threatened.

significance to humans

None known.

No common name

Holjapyx diversiunguis

family

Japygidae

taxonomy

Japyx diversiunguis Silvestri, 1911, Yosemite National Park, California, United States.

other common names

None known.

physical characteristics

Length 0.2–0.3 in (6–8 mm). Body pale yellow, tenth abdominal segment and forceps dark brown. Antennae have 26 segments. Forceps each with one prominent tooth. Species identification accomplished by examination of the setae and abdomen.

distribution

Central one-third of California, United States, from the coast east to the crest of the Sierra Nevadas.

habitat

In soil and on the surface, under rocks and damp leaves.

behavior

A deep burrower, descending to depths around 30 in (76 cm).

feeding ecology and diet

Nothing is known.

reproductive biology

Report of female with eight small larvae suggests parental care. Females probably also guard their small clutch of eggs.

conservation status

Not threatened.

significance to humans

None known.

Resources

Books

Condé, B., and Pagés, J. "Diplura." In The Insects of Australia: A Textbook for Students and Research Workers. 2nd edition, edited by CSIRO. Carlton, Australia: Melbourne University Press, 1991.

Ferguson, L. M. "Insecta: Diplura." In Soil Biology Guide, edited by D. Dindal. New York: John Wiley & Sons, 1990.