Arthropoder

Arthropoder, commonly referred to as arthropods, is a broad and diverse phylum of invertebrate animals characterized by a segmented body, jointed limbs, and an exoskeleton made of chitin. The exoskeleton provides protection and support but requires periodic molting as the organism grows. The combination of segmentation, jointed appendages, and an adaptable body plan has enabled arthropods to colonize virtually all habitats, from deep oceans to deserts and high mountains.

Arthropods are divided into four major groups: Hexapoda (primarily insects and their relatives), Crustaceans (crabs, shrimp, lobsters), Myriapoda (centipedes and millipedes), and Chelicerata (spiders, scorpions, mites, and horseshoe crabs). Some extinct lineages, such as trilobites, are known from fossils. Common features across the groups include a ventral nerve cord, an open circulatory system, and sensory structures such as antennae or multiple simple eyes.

Most arthropods possess specialized respiratory systems: book lungs or tracheae in various groups, and gills in many aquatic crustaceans. Body plans vary, with forms adapted for flight in many hexapods, predation in arachnids, and rapid swimming in crustaceans. Growth typically occurs through molting (ecdysis), controlled by hormonal cycles, allowing size increases but creating vulnerability during shedding.

Ecology and human relevance: arthropods play central roles as pollinators, decomposers, and sources of food for other animals. They are also important vectors of disease and major agricultural pests, yet they provide valuable products and services, such as silk, honey, and biocontrol agents. Studying arthropoder contributes to understanding evolution, development, and the dynamics of ecosystems.