"Arthropod" - what is it, definition of the term
Joint‑segmented invertebrates of the phylum characterized by a hardened exoskeleton, articulated limbs, and a segmented body plan; this group includes organisms such as ticks, true bugs, lice, and fleas, all of which possess a chitinous cuticle and undergo molting during growth.
Detailed information
Joint‑legged invertebrates constitute the largest animal phylum, characterized by a chitinous exoskeleton, segmented bodies and articulated appendages. Their development proceeds through molting, which permits growth despite the rigid outer covering. This group includes organisms of medical and economic relevance such as ticks, true bugs, lice and fleas.
Ticks are arachnids with a capitulum adapted for blood feeding. Their life cycle comprises egg, larva, nymph and adult stages; each active stage requires a vertebrate host for a prolonged parasitic attachment. Salivary secretions contain anticoagulants and immunomodulatory compounds, facilitating pathogen transmission. Species such as Ixodes scapularis and Rhipicephalus sanguineus serve as vectors for Borrelia, Rickettsia and viral agents.
True bugs belong to the order Hemiptera and display piercing‑sucking mouthparts. Many are phytophagous, but families like Cimicidae (bed bugs) have evolved hematophagy. Their cuticle is thin, allowing rapid expansion after feeding. Reproductive output is high; females lay hundreds of eggs in concealed locations. Bed bug infestations trigger cutaneous reactions and may cause secondary infections.
Lice are obligate ectoparasites of mammals and birds, classified within the order Phthiraptera. They exhibit dorsoventrally flattened bodies, facilitating movement through host hair or feathers. Three major groups exist: chewing lice (Mallophaga), sucking lice (Anoplura) and avian chewing lice. Life cycles are direct, lacking free‑living stages; development from egg to adult occurs on the host within 2–4 weeks. Infestations cause irritation, anemia and can transmit bacterial pathogens.
Fleas are small, laterally compressed insects of the order Siphonaptera. Their hind legs are adapted for jumping, providing rapid host transfer. The adult female produces 20–50 eggs per gonotrophic cycle, which are deposited in the host’s environment. Larvae develop in organic debris, feeding on organic matter and adult flea feces. Species such as Ctenocephalides felis and Xenopsylla cheopis transmit Yersinia pestis, Bartonella and tapeworms.
Key morphological traits shared across these groups include a hardened exoskeleton, segmented body plan and specialized mouthparts for hematophagy or plant feeding. Their ecological impact stems from direct parasitism of vertebrate hosts and indirect effects as disease vectors. Control strategies focus on interrupting life cycles, applying insecticidal agents and managing host habitats.