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Myriapods are a subphylum of arthropods that include centipedes, millipedes, sinphylans, and pauropods. They are the earliest known land animals, with one millipede fossil dating back to 428 million years ago. Millipedes and centipedes are the most familiar and largest myriapods, with millipedes being voracious, fast, and venomous predators. Centipedes are less fearsome and look like extended pill bugs. Millipedes exhibit more diversity than centipedes, with around 8,000 known species.
Myriapods are members of Myriapoda, a subphylum of arthropods. They include the familiar centipedes and centipedes as well as the very small and rarely seen sinphylans and pauropods. Myriapods are the earliest known land animals, with one millipede fossil dating to the Late Silurian, 428 million years ago. It is known to have been terrestrial due to the presence of small breathing holes called spiracles. There is a possibility that myriapods are even older, as molecular evidence points to a major episode of diversification in an even older era, the Cambrian, and there are some Cambrian fossils that may be myriapods.
The most familiar and largest myriapods are millipedes and centipedes, many-legged arthropods whose number of legs ranges from fewer than ten to 750, depending on the species. Both live in decaying plant material, although millipedes actually eat leaf litter while millipedes prowl for prey such as small insects. Millipedes and centipedes are strikingly different in appearance, as centipedes have long legs that stick out to the sides while centipedes usually have their legs contained under the body. All myriapod species are terrestrial, but millipedes can be amphibious in rare cases.
Millipedes are voracious, fast, and venomous predators. They hunt mainly at night and are terrifying in appearance, although they are of little danger to humans. Unusual for a taxon, they are exclusively predatory, and the distinguishing feature of the group is a set of venomous forelimbs. Their name means “one hundred feet,” though they usually only have a couple of dozen. The smallest centipede is Nannarup hoffmani, which is about half an inch long, while the largest is Scolopendra gigantea, the Amazon giant centipede, which reaches 30 cm in length. The Amazonian giant centipede is known to eat bats (catching them in flight), rodents, and large spiders. In all, there are about 12 known species of millipedes.
Centipedes are less fearsome than centipedes, both in appearance and behavior. They look like extended pill bugs, snaking through debris for edible leaf matter. Millipedes move slower than centipedes and have more body segments and legs. The defining feature of millipedes is that each pair of body segments are fused into a single unit, making each segment appear to have two pairs of legs. Millipedes exhibit more diversity than millipedes, with around 8,000 known species. One species, Illacme plenipes, a rare millipede found in central California, has 750 legs, the most of any known animal.
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