Millipedes

Millipedes are a species of arthropods that have two pairs of jointed legs on most of their body segments; they are classified as Diplopoda (Millipede Scientific Name) in scientific terms, which is derived from this characteristic. Two single segments are glued together to form each double-legged segment. 

Pill millipedes are thinner and can roll into a disk, while most millipedes have very elongated cylindrical or flattened bodies of more than 20 segments. About the fact that the word Millipede meaning comes from the Latin word "thousand feet," no recognized species has 1,000 legs; Illacme plenipes holds the record with 750. The majority of millipedes are detritivores. 

Millipedes consume rotting leaves and other dead plant matter. Some consume mushrooms or drink plant fluids, while others are predators. Humans are normally unaffected by millipedes, but some may become household or garden pests. Millipedes are particularly unwelcome in greenhouses, where they can seriously damage emerging seedlings. Although the tiny bristle millipedes are coated with tufts of detachable bristles, most millipedes protect themselves with a combination of chemicals secreted from pores along the body. Its primary defence strategy is to curl into a tight coil, shielding its legs and other sensitive body parts under a hard exoskeleton. 

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Classification

The Diplopoda is classified into sixteen orders and two subclasses of living organisms. Polyxenida is the only order in the Penicillata subclass (bristle millipedes). All other millipedes are members of the Chilognatha subclass, which is divided into two infraclasses: Pentazonia (short-bodied pill millipedes) and Helminthomorpha (worm-like millipedes), which includes the vast majority of species. Based on Shear, 2011, and Shear & Edgecombe, 2010, the higher-level classification of millipedes is presented below (extinct groups). Recent cladistic and molecular studies have cast doubt on the above-mentioned classification systems, and the status of the orders Siphoniulida and Polyzoniida, in particular, is still unclear. The placement and locations of extinct groups that are only known from fossils are speculative and unresolved. The author citation follows each name: the name of the person who invented the name or identified the category, even though they are not at the current level.

Evolution

During the Silurian era, millipedes were among the first animals to colonize soil. Mosses and primitive vascular plants were most likely eaten by early forms. The Archipolypoda ("ancient, many-legged ones''), which contains the oldest known terrestrial animals, and the Arthropleuridea, which contains the largest known land invertebrates, are the two main classes of millipedes whose members are now extinct. Pneumodesmus newmani, the first known land organism, was a 1 cm (0.4 in) long archipolypodan that lived 428 million years ago in the upper Silurian and had spiracles (breathing holes) that attested to its air-breathing habits. Arthropleura is the largest known land-dwelling invertebrate on record during the Upper Carboniferous (340 to 280 million years ago), exceeding lengths of at least 2 m. (6 ft 7 in).  Millipedes also provide the earliest signs of chemical defence, with ozopores, which are protective gland openings found in Devonian fossils. In the oxygen-rich habitats of the Devonian and Carboniferous periods, millipedes, centipedes, and other terrestrial arthropods grow to enormous sizes in contrast to modern animals, with some reaching lengths of over one meter. Arthropods shrank in size as oxygen levels dropped over time.

Living Groups

The tradition of scientific millipede classification began with Carl Linnaeus, who described seven species of Julus as "Insecta Aptera'' in his 10th edition of Systema Naturae in 1758. In 1802, French zoologist Pierre André Latreille suggested the name Chilognatha for the first group of what is now known as the Diplopoda, and Johann Friedrich von Brandt, a German naturalist, published the first accurate classification in 1840. Henri Marie Ducrotay de Blainville, a French zoologist, invented the term Diplopoda in 1844. From 1890 to 1940, millipede taxonomy was inspired by a limited number of researchers at any given time, with substantial contributions from Carl Attems, Karl Wilhelm Verhoeff, and Ralph Vary Chamberlin, who each identified over 1,000 species, as well as Orator F. Cook, Filippo Silvestri, R. I. Pocock, and Henry W. Brölemann. 

The science of diplopodology flourished during this period, with the highest numbers of species descriptions in history, often reaching 300 a year. In his Nomenclator Generum et Familiarum Diplopodorum, published in 1971, Dutch biologist C. A. W. Jeekel published a systematic listing of all recognized millipede genera and families listed between 1758 and 1957, credited with launching the "classic age" of millipede taxonomy. 

Richard L. Hoffman, an American biologist, published a description of millipedes in 1980, recognizing the Penicillata, Pentazonia, and Helminthomorpha, and Henrik Enghoff of Denmark published the first phylogenetic study of millipede orders using modern cladistic methods in 1984. Despite more recent molecular research suggesting contrasting relationships, a 2003 classification by American myriapodologist Rowland Shelley is close to the one suggested by Verhoeff and remains the generally accepted classification scheme.

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Distinction Between Centipede and Millipede

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Characteristics

Millipedes have a wide range of body types and proportions, varying from 2 mm (0.08 in) to 35 cm (14 in) in length, with as little as eleven to over a hundred segments. The types of Millipedes are often black or brown in colour, with a few brightly coloured species including Red Millipede and others with aposematic colouring to indicate that they are poisonous. Motyxia species are bioluminescent and contain cyanide as a chemical defence. The big millipede classes have a wide range of body types. The exoskeleton of the tiny bristle millipedes in the basal subclass Penicillata is smooth and uncalcified, and it is coated in conspicuous setae or bristles. The other millipedes in the Chilognatha subclass have a hardened exoskeleton. The chilognaths are classified into two infraclasses: Pentazonia, which includes groups with comparatively small bodies like pill millipedes, and Helminthomorpha ("worm-like") millipedes, which includes the vast majority of species with long, many-segmented bodies. 

Head

The head of a millipede is usually triangular on top and flattened on the bottom, with a pair of enormous mandibles in front of a plate-like assembly known as a gnathochilarium ("jaw lip"). A single pair of antennae with seven or eight segments and a set of sensory cones at the tip can be found on the head. The Tömösváry organs, which are shaped like tiny oval rings posterior and lateral to the base of the antennae, are found in many orders. Their function is unclear, but they are found in some centipedes and may be used to detect humidity or light levels in the atmosphere. Millipede eyes are made up of a group or patch of clear flat-lensed ocelli on either side of the head. Ocular fields or ocellaria are other names for these patches. Many millipede species, including the whole orders Polydesmida, Siphoniulida, Glomeridesmida, Siphonophorida, and Platydesmida, as well as cave-dwelling millipedes like Causeyella and Trichopetalum, had vision-capable ancestors who have since lost their sight and became blind.

Body

Millipede bodies can be flattened or cylindrical, and they are made up of several metameric segments with an exoskeleton made up of four chitinous plates: one above (the tergite), one on either side (pleurites), and one on the underside (sternite) where the legs join. These plates are fused to various degrees in several millipedes, such as Merocheta and Juliformia, and may often form a single cylindrical ring. Since the plates are impregnated with calcium salts, they are usually strong. Millipedes are vulnerable to water depletion due to their inability to close their permanently open spiracles and the absence of a waxy cuticle in most animals. As a result, with a few exceptions, they must spend the majority of their time in damp or humid conditions. The collum is the first segment behind the head that is legless (from the Latin for neck or collar). The "haplosegments" are the second, third, and fourth body segments, which each have a single pair of legs (the three haplosegments are sometimes referred to as a "thorax").

Internal Organs

Millipedes breathe from two pairs of spiracles at the base of the legs, positioned ventrally on each segment. Each one attaches to a tracheae device and opens into an internal pouch. The aorta, which extends into the brain, connects the heart to the rest of the body. Two pairs of malpighian tubules are found in the mid-section of the gut and serve as excretory organs. The digestive tract is a clear tube that contains two pairs of salivary glands that aid in the digestion of food. 

Reproduction and Growth

Millipedes have a wide range of mating types and configurations to choose from. Mating occurs indirectly in the Polyxenida (bristle millipedes) order: males deposit spermatophores into webs secreted by special glands, and females pick up the spermatophores. The gonopods are distributed differently in different groups: in males of the Pentazonia, they are classified as telopods and can also act in grasping females, while in Helminthomorpha – the vast majority of species – they are located on the seventh body segment and are known as gonopods. Just a few animals are parthenogenetic, meaning they have few to no males. Males in all other millipede classes have one or two pairs of adapted legs known as gonopods that are used to transfer sperm to the female during copulation. Gonopods come in a variety of shapes and sizes, ranging from simple structures that look like walking legs to intricate structures that don't look like legs at all. The gonopods are held retracted within the body in some classes, whilst they project forward parallel to the body in others. 

Ecology

Habitat and Distribution

Millipedes can be found on every continent except Antarctica and in nearly every terrestrial ecosystem, extending from the Arctic Circle in Iceland, Norway, and Central Russia to Santa Cruz Province in Argentina. They live in leaf litter, dead trees, or dirt on the forest floor, with a preference for humid conditions. Millipedes are most common in wet deciduous forests, where densities of over 1,000 individuals per square metre can be found. Coniferous trees, caves, and alpine landscapes are examples of other environments. Deserticolous millipedes, such as Orthoporus ornatus, may have developed adaptations such as a waxy epicuticle and the capacity to absorb water from unsaturated air. Some plants can withstand freshwater flooding and can stay submerged for up to 11 months. A few species can live in saline environments and are found along the seashore.

Burrowing

Millipedes' diplosegments have evolved in tandem with their burrowing habits, and almost all millipedes live mostly underground. They burrow using three major methods: bulldozing, wedging, and boring. The collum is the part of the exoskeleton that leads the way for members of the orders Julida, Spirobolida, and Spirostreptida as they lower their heads and barge their way through the substrate. Flat-backed millipedes of the order Polydesmida appear to wedge their front end into a horizontal crevice and then expand it by pressing upwards with their wings, with the paranota serving as the main lifting surface in this case. Boring is a term used by Polyzoniida members. Some millipedes have abandoned their burrowing habits and instead live above ground. This may be due to the fact that they are too small to burrow, or that they are too massive to make the attempt worthwhile, or that they travel relatively quickly (for a millipede) and are aggressive predators.

Diet

Specific consumption rates for individual species vary from 1 to 11% of total leaf litter, depending on species and area, and millipedes can eat nearly all of the leaf litter in a region collectively. Detritivores, or millipedes that feed on decomposing leaves, faeces, or organic matter combined with soil, make up the majority of millipedes. In the millipede gut, the leaf litter is fragmented and excreted as pellets of leaf particles, algae, fungi, and bacteria, facilitating microorganism decomposition. Millipedes play an important role in promoting microbial decomposition of leaf litter in tropical forests where earthworm numbers are limited. Some millipedes are herbivores, meaning they feed on living plants, and some species can be major crop pests. Polyxenida millipedes graze algae from bark, while Platydesmida millipedes eat fungi. A few animals are omnivorous, although some in the Callipodida and Chordeumatida families are carnivorous on spiders, centipedes, earthworms, and snails.

Conclusion

Millipede insects are among the oldest known land animals, first appearing in the Silurian period. Any extinct specimens reached heights of over 2 m (6 feet 7 in); the largest human species attain lengths of 27 to 38 cm (11 to 15 in). The giant African millipede is the world's longest-living mammal.

Millipedes have long been thought to be the most closely related myriapods to the tiny pauropods, but some molecular evidence contradicts this. Millipede insects are different from centipedes (class Chilopoda), which are venomous, carnivorous, and have only a single pair of legs on each body segment. Diplopodology is the biological study of millipedes, and a diplopodologist is a scientist who studies them.

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