"Surface" - what is it, definition of the term
An external boundary that separates a body from its surroundings, represented by a continuous two‑dimensional sheet of points, forms the outermost layer of any object; in arthropods such as ticks, bugs, lice, and fleas, this layer consists of the cuticle and epidermal interface that governs environmental interaction, determines texture, and provides the substrate for sensory structures.
Detailed information
The external layer of arachnids and insects consists of a chitinous cuticle that provides protection, prevents desiccation, and serves as an attachment site for sensory structures. This covering is secreted by epidermal cells and undergoes sclerotization to attain rigidity. Molting replaces the old cuticle with a new one, allowing growth.
Ticks possess a multi‑layered shield composed of a dorsal scutum, ventral plates, and a flexible integument beneath. The scutum varies in size between sexes; males retain a complete scutum, while females expand it during engorgement. Sensory setae and Haller’s organ are embedded in the cuticle, enabling host detection.
True bugs display a dorsally flattened exoskeleton with a leathery forewing (hemelytron) that protects the membranous hind wing. The integument includes a waxy epicuticle that reduces water loss. Mouthparts are concealed within a rostrum, and the cuticle houses mechanoreceptors for vibration detection.
Lice have a compact, scale‑covered outer covering that adheres tightly to the host’s skin. The scale pattern differs among species, providing taxonomic clues. The cuticle is thin, allowing rapid diffusion of gases, while the underlying epidermis produces enzymes for keratin digestion.
Fleas feature a smooth, laterally compressed cuticle that facilitates movement through host fur. The exoskeleton is reinforced with sclerotized plates, especially on the thorax and abdomen. A hydrophobic layer prevents drowning during immersion in host fluids. Sensory hairs on the integument detect temperature and carbon‑dioxide gradients.
Common structural elements across these arthropods: