Pauropoda
Encyclopedia
Pauropods are small, pale, centipede
-like arthropod
s. They form the order
Pauropodina, belonging to the monotypic class
Pauropoda. About 500 species
in four families are found worldwide, living in soil
and leaf mold. They look rather like centipede
s, but are probably the sister group to millipede
s.
The name is derived from the Greek roots "small" and "foot".
, they seem to be an old group closely related to the millipede
s (Diplopoda). Their head capsules show great similarities to millipedes: both have three pairs of mouthparts and the genital openings occur in the anterior part of the body. Moreover, both groups have a pupoid phase at the end of the embryonic development. The two groups probably have a common origin.
There are two orders: Hexamerocerata and Tetramerocerata. Hexamerocerata has a 6-segmented and strongly telescopic antennal stalk and a 12-segmented trunk with 12 tergites and 11 pairs of legs. The representatives are white and proportionately long and large. The one family in this order, Millotauropodidae, has one genus and a few species. Tetramerocerata has a 4-segmented and scarcely telescopic antennal stalk, 6 tergites, and 8–10 pairs of legs. Representatives of this order are often small (sometimes very small), and white or brownish. Most species have nine pairs of legs as adults. The four families include Pauropodidae, Afrauropodidae, Brachypauropodidae, and Eurypauropodidae. Most genera and species belong to the family Pauropodidae.
Hexamerocerata has a purely tropical range, while in Tetramerocerata, most genera are subcosmopolitan.
There are 12 trunk segments, but the number of tergites is always less. The head is small, directed downwards, without eyes but with eyelike sensory organs. Behind the last trunk segment, there is an anal segment, the pygidium, which is horizontally divided. It has a most peculiar structure posteriorly, the anal plate (0.01 millimetre in diameter), which is the greatest factor for identification purposes. Almost every species has a unique plate that is characterized by its shape (form, size, cuticular structure) and, if any, its appendage
s (number, length, thickness, direction, surface structure, insertion points). Each species can be identified from this plate, even at the first larval stage.
Pauropods are so small that they have often been overlooked, even by many trained soil zoologists. Consequently, pauropods are little known by the general public. A single species (Saintpaulia sp.) has recently been found feeding on and damaging cuttings in a greenhouse in the Netherlands. They are not dangerous to humans.
The food habits of most species are unknown, but some can eat mold or suck out fungal hyphae; at least one species even eats root hairs. Most species move swiftly with intermittent rushes very much like a miniature mouse. Reduced agility occurs in the families Brachypauropodidae and Eurypauropodidae.
has three pairs of legs, but that number increases with each molt so that adult species may have 9 to 11 pairs of legs. They have neither eye
s nor heart
s. The body segments have ventral tracheal/spiracular pouches forming apodemes similar to those in millipede
s and Symphyla
, although the trachea
usually connected to these structures are absent in most species. They have soft, cylindrical bodies and paired antennae
.
Centipede
Centipedes are arthropods belonging to the class Chilopoda of the subphylum Myriapoda. They are elongated metameric animals with one pair of legs per body segment. Despite the name, centipedes can have a varying number of legs from under 20 to over 300. Centipedes have an odd number of pairs of...
-like arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
s. They form the order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
Pauropodina, belonging to the monotypic class
Class (biology)
In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...
Pauropoda. About 500 species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
in four families are found worldwide, living in soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
and leaf mold. They look rather like centipede
Centipede
Centipedes are arthropods belonging to the class Chilopoda of the subphylum Myriapoda. They are elongated metameric animals with one pair of legs per body segment. Despite the name, centipedes can have a varying number of legs from under 20 to over 300. Centipedes have an odd number of pairs of...
s, but are probably the sister group to millipede
Millipede
Millipedes are arthropods that have two pairs of legs per segment . Each segment that has two pairs of legs is a result of two single segments fused together as one...
s.
The name is derived from the Greek roots "small" and "foot".
Evolution and systematics
Though no fossil pauropods have been found from before the time of the Baltic amberBaltic amber
The Baltic region is home to the largest known deposit of amber, called Baltic amber or succinite, with about 80% of the world's known amber found there. It dates from 44 million years ago...
, they seem to be an old group closely related to the millipede
Millipede
Millipedes are arthropods that have two pairs of legs per segment . Each segment that has two pairs of legs is a result of two single segments fused together as one...
s (Diplopoda). Their head capsules show great similarities to millipedes: both have three pairs of mouthparts and the genital openings occur in the anterior part of the body. Moreover, both groups have a pupoid phase at the end of the embryonic development. The two groups probably have a common origin.
There are two orders: Hexamerocerata and Tetramerocerata. Hexamerocerata has a 6-segmented and strongly telescopic antennal stalk and a 12-segmented trunk with 12 tergites and 11 pairs of legs. The representatives are white and proportionately long and large. The one family in this order, Millotauropodidae, has one genus and a few species. Tetramerocerata has a 4-segmented and scarcely telescopic antennal stalk, 6 tergites, and 8–10 pairs of legs. Representatives of this order are often small (sometimes very small), and white or brownish. Most species have nine pairs of legs as adults. The four families include Pauropodidae, Afrauropodidae, Brachypauropodidae, and Eurypauropodidae. Most genera and species belong to the family Pauropodidae.
Hexamerocerata has a purely tropical range, while in Tetramerocerata, most genera are subcosmopolitan.
Physical characteristics
These white or brownish animals are blind and have many partly unusual sensory organs. There are five pairs of long sensory hairs on the trunk. The antennae are complicated, biramous, with three flagellae. They are provided with different organs to help the animal analyze the surroundings, among them the end organs of the flagellae and the globulus at the distal part of the lower antennal branch.There are 12 trunk segments, but the number of tergites is always less. The head is small, directed downwards, without eyes but with eyelike sensory organs. Behind the last trunk segment, there is an anal segment, the pygidium, which is horizontally divided. It has a most peculiar structure posteriorly, the anal plate (0.01 millimetre in diameter), which is the greatest factor for identification purposes. Almost every species has a unique plate that is characterized by its shape (form, size, cuticular structure) and, if any, its appendage
Appendage
In invertebrate biology, an appendage is an external body part, or natural prolongation, that protrudes from an organism's body . It is a general term that covers any of the homologous body parts that may extend from a body segment...
s (number, length, thickness, direction, surface structure, insertion points). Each species can be identified from this plate, even at the first larval stage.
Pauropods are so small that they have often been overlooked, even by many trained soil zoologists. Consequently, pauropods are little known by the general public. A single species (Saintpaulia sp.) has recently been found feeding on and damaging cuttings in a greenhouse in the Netherlands. They are not dangerous to humans.
Habitat
In most environments, their occurrence is patchy and the population sparse. However, sometimes they have been reported to have several thousand specimens per square meter, even in agricultural habitats. They are easy to find under stones and molting tree branches that have good contact with the underlying moist soil. They are also under moss carpets. They inhabit many plant communities and soil types and are most abundant in a zone about 3.9–7.8 in (10–20 cm) deep. However, though they cannot burrow, they can follow root canals and crevices in much deeper levels, down to the groundwater surface.Behavior
Pauropods have a patchy occurrence and can often be found aggregated on the underside of stones and tree branches. They are most often swift runners, with mouse-like intermittent rushes. The species most often observed can turn its body almost 180°. Pauropods are shy of light and try to disappear in crevices and soil clumps as soon as possible. The antennae rotate constantly with an unusually high rapidity to examine the environment. The sexes are separate, and males deposit small spherical sperm-packets in the soil, which the females seek and pick up. Nothing is known about other types of social behavior and communication. Their display and territoriality are unknown. Vertical migration occurs when there are changes in soil moisture.The food habits of most species are unknown, but some can eat mold or suck out fungal hyphae; at least one species even eats root hairs. Most species move swiftly with intermittent rushes very much like a miniature mouse. Reduced agility occurs in the families Brachypauropodidae and Eurypauropodidae.
Reproductive biology
Pauropods are dioeceous and progoneate. The egg develops in a short pupoid phase before the first larval instar appears. In Tetramerocerata, the first larval instar has three pairs of legs, and is then followed by instars with five, six, and eight pairs of legs; the adults have eight, nine, or 10 pairs of legs. In Hexamerocerata, the first larval instar has six pairs of legs. Parthenogenetic reproduction seems to occur, particularly in areas with unfavorable environmental conditions.Anatomy
Pauropod size ranges from 0.5 to 2 mm (0.0196850393700787 to 0.078740157480315 ). The first instarInstar
An instar is a developmental stage of arthropods, such as insects, between each molt , until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or...
has three pairs of legs, but that number increases with each molt so that adult species may have 9 to 11 pairs of legs. They have neither eye
Eye
Eyes are organs that detect light and convert it into electro-chemical impulses in neurons. The simplest photoreceptors in conscious vision connect light to movement...
s nor heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
s. The body segments have ventral tracheal/spiracular pouches forming apodemes similar to those in millipede
Millipede
Millipedes are arthropods that have two pairs of legs per segment . Each segment that has two pairs of legs is a result of two single segments fused together as one...
s and Symphyla
Symphyla
Symphylans, also known as garden centipedes or glasshouse symphylans, are soil-dwelling arthropods of the class Symphyla in the subphylum Myriapoda. Symphylans resemble centipedes, but are smaller and translucent. They can move rapidly through the pores between soil particles, and are typically...
, although the trachea
Invertebrate trachea
The invertebrate trachea refers to the open respiratory system composed of spiracles, tracheae, and tracheoles that terrestrial arthropods have to transport metabolic gases to and from tissues....
usually connected to these structures are absent in most species. They have soft, cylindrical bodies and paired antennae
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....
.