Myriapods: The Many-Legged Arthropods

Scientific Name: Myriapoda

Centipede
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Myriapods (Myriapoda) are a group of arthropods that includes millipedes, centipedes, pauropods, and symphylans. There are about 15,000 species of myriapods alive today. As their name implies, myriapods (Gr. myriads, a myriad, + photos, foot) are noted for their having many legs. The number of legs a myriapod has varied from species to species and there is a wide range. Some species have fewer than a dozen legs, while others have many hundreds of legs.

The Illacme pipes, a millipede that inhabits central California, is the current record holder for myriapod leg count—this species has 750 legs which are the most of all known myriapods.

Oldest Myriapods

The earliest fossil evidence for myriads dates back to the late Silurian, about 420 million years ago. Molecular evidence indicates that the group first evolved before this, though, perhaps as early as the Cambrian Period. Some Cambrian fossils show some similarities to early myriapods, indicating that their evolution could have been underway at that time.

Key Characteristics of Myriapods

The key characteristics of myriapods include:

  • many pairs of legs
  • two body sections (head and trunk)
  • one pair of antennae on the head
  • simple eyes
  • mandibles and maxillae
  •  respiratory exchange occurs through a tracheal system

Physical Characteristics of Myriapods

Myriapods have a body that is divided into two tagmata (body sections)—a head and a trunk.

The trunk is further divided into multiple segments and each segment has a pair of appendages (legs). Myriapods have a pair of antennae on their head and a pair of mandibles and two pairs of maxillae (millipedes only have one pair of maxillae).

Centipedes have a round flat head with one pair of antennae, a pair of maxillae and pair of large mandibles.

Centipedes have limited vision (and some species have no eyes at all). Those that have eyes can only perceive differences in light and dark but lack true vision.

Millipedes have a rounded head but unlike centipedes, it is flat only on the bottom. Millipedes have a pair of large mandibles, a pair of antennae, and (also like centipedes) limited vision. The body of millipedes is cylindrical in shape. Millipedes feed on detritus such as decomposing vegetation, organic material, and feces. Millipedes are prey for a variety of animals including amphibians, reptiles, mammals, birds, and other invertebrates. Millipedes lack the venomous claws that centipedes. This means millipedes must curl into a tight coil to protect themselves. Millipedes generally have between 25 and 100 segments. The thoracic segments and each have one pair of legs while the abdominal segments bear two pairs of legs each.

Myriapods Habitat

Myriapods inhabit a variety of habitats but are most abundant in forests. They also inhabit grasslands, scrublands, and deserts. Most myriapods are detritivores that live on decaying plant material. Centipedes are the exception to this rule, they are mainly nocturnal predators. The two less-familiar groups of myriapods, the sauropods, and the symphylans are small organisms (some species are microscopic) that live in soil.

Classification

Myriapods are classified within the following taxonomic hierarchy:

Animals > Invertebrates > Arthropods > Myriapods

Myriapods are divided into the following taxonomic groups:

  • Centipedes (Chilopoda) - There are more than 3,000 species of centipedes alive today. Members of this group include stone centipedes, tropical centipedes, soil centipedes, and house centipedes. Centipedes are carnivorous and the first segment of their body is equipped with a pair of venomous claws.
  • Millipedes (Diplopoda) - There are about 12,000 species of millipedes alive today. Members of this group include polyxenidans, chordeumatidans, platydesmidans, siphonophoridans, polydesmidans, and many others.