Trigonotarbida
Trigonotarbids were an extinct order of arachnids known from the Silurian to the Permian. They had segmented abdomens and no tail.
Arachnid: An arthropod in the class Arachnida, including spiders, scorpions, mites, and their extinct relatives. Trigonotarbids are an extinct arachnid order, sharing the group's basic body plan.
Silurian: A geologic period from about 443 to 419 million years ago, marked by early terrestrial ecosystems. The earliest known trigonotarbids appear in Silurian deposits.
Palaeocharinus: An extinct genus of trigonotarbid arachnids known from Devonian fossil deposits. Its fossils are among the best-known examples of early members of the order.
Spider: An arachnid in the order Araneae, typically bearing silk-producing spinnerets and a narrow waist. Spiders lack the conspicuously segmented abdomen characteristic of trigonotarbids.
Opisthosoma: The posterior body region of a chelicerate, commonly called the abdomen in arachnids. Its visible segmentation is a defining feature of trigonotarbids.
Devonian: A geologic period from about 419 to 359 million years ago, when terrestrial plants and animals diversified. Trigonotarbids are known from deposits spanning this period.
Anthracomartus: An extinct genus of trigonotarbids known from Carboniferous and Permian deposits. Its fossils show the order persisted beyond the Devonian.
Scorpion: An arachnid in the order Scorpiones, with pincers and a segmented tail ending in a venomous sting. The scorpion's conspicuous tail contrasts with the tailless trigonotarbid body.
Prosoma: The anterior body region of a chelicerate, bearing the eyes, mouthparts, and walking legs. Fossils preserve this region alongside the segmented opisthosoma.
Carboniferous: A geologic period from about 359 to 299 million years ago, noted for extensive coal-forming wetlands. Carboniferous fossils provide a substantial record of the order.