Robustoida

Robustoida refers to a group of extinct marine arthropods that lived during the Paleozoic Era, primarily in the Cambrian and Ordovician periods. These organisms are characterized by their distinctive, robust exoskeletons, which provided significant protection. While their exact taxonomic placement has been debated, they are generally considered to be part of the Chelicerata subphylum, making them distant relatives of modern spiders, scorpions, and horseshoe crabs.

Fossil evidence suggests that robustoids were bottom-dwellers, likely inhabiting marine environments ranging from shallow coastal waters to deeper seafloor habitats. Their morphology indicates adaptations for predation or scavenging. Key features often include a series of segmented body plates and specialized appendages. The specific details of their sensory organs, feeding mechanisms, and reproductive strategies remain largely inferred from their fossilized remains.

The term "robustoida" is not a formal taxonomic rank but rather a descriptive grouping used by paleontologists to refer to a set of related Cambrian and Ordovician arthropod fossils that share certain robust, often heavily calcified, exoskeletal features. Studying these fossils provides valuable insights into the early evolution of arthropod body plans and the diverse ecosystems of the Paleozoic oceans. Their extinction is generally linked to broader Paleozoic extinction events.