How can the external appearance of ticks be described? - briefly
Ticks are small arachnids, 1–5 mm in length, with a rounded, flattened body and a dorsal shield that is hard in some species and soft in others. Their four legs project from the front, and a beak‑like mouthpart extends from the underside for blood‑feeding.
How can the external appearance of ticks be described? - in detail
Ticks are small arachnids ranging from 1 mm in early stages to 12 mm in engorged adults. The body is divided into two primary regions. The anterior capitulum houses the chelicerae and hypostome, which appear as a short, tapering structure equipped with barbs for attachment. The posterior idiosoma comprises the bulk of the organism and includes several distinct features.
- Scutum: In hard‑ticked species (Ixodidae) the dorsal surface of the idiosoma bears a rigid, shield‑like plate. The scutum may be complete in males and partial in females, often displaying species‑specific patterns of color, punctation, or ornamentation.
- Legs: Four pairs of legs emerge from the ventral side. Each leg is segmented into coxa, trochanter, femur, patella, tibia, and tarsus, ending in claws that enable grasping of the host. Leg length varies with developmental stage; larvae possess proportionally shorter legs than nymphs and adults.
- Eyes: Some soft‑ticked species (Argasidae) possess simple eyes located laterally on the dorsal surface; many hard ticks lack functional eyes altogether.
- Festoons: Marginal rectangular plates, typically eight to twelve, line the posterior edge of the idiosoma in many hard ticks. They serve as flexible expansion zones during blood feeding.
- Spiracular plates: Paired openings on the ventral side allow respiration; the plates are often visible as small, raised structures near the posterior margin.
- Coloration: Unfed ticks are generally brown to reddish‑brown; engorgement produces a dramatic expansion and a pale, translucent appearance. Some species exhibit distinctive markings, such as a pale central area on the scutum or dark lateral spots.
Life‑stage differences affect external morphology. Eggs are smooth, oval, and lack visible segmentation. Larvae (seed ticks) have a simple, unornamented scutum and lack festoons. Nymphs develop a partially hardened scutum and begin to show festoons. Adults possess a fully formed scutum (complete in males, partial in females) and well‑defined festoons and spiracular plates. Sexual dimorphism is evident: males retain a complete scutum covering the entire dorsal surface, whereas females have a reduced scutum to accommodate abdominal expansion during feeding.
Overall, the external appearance of ticks combines a compact, segmented body plan with specialized structures for attachment, respiration, and host detection, each varying systematically across species and developmental stages.