Arachnids are a class (Arachnida) of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although the front pair of legs in some species has converted to a sensory function, while in other species, different appendages can grow large enough to take on the appearance of extra pairs of legs. The term is derived from the Greek word ἀράχνη (aráchnē), meaning “spider”.
Almost all extant arachnids are terrestrial. However, some inhabit freshwater environments and, with the exception of the pelagic zone, marine environments as well. They comprise over 100,000 named species, including spiders, scorpions, harvestmen, ticks, mites and Solifugae. (Wikipedia)
In biology, a nymph is the immature form of some invertebrates, particularly insects, which undergoes gradual metamorphosis (hemimetabolism) before reaching its adult stage.Unlike a typical larva, a nymph’s overall form already resembles that of the adult. In addition, while a nymph moults it never enters a pupal stage. Instead, the final moult results in an adult insect. Nymphs undergo multiple stages of development called instars. (Wikipedia)
An instar (from the Latin “form”, “likeness”) is a developmental stage ofarthropods, such as insects, between each molt (ecdysis), until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or changes in the number of body segments. Some arthropods can continue to molt after sexual maturity, but these subsequent molts are generally not called instars.
For most insect species the term instar is used to denote the developmental stage of the larval or nymphal forms of holometabolous (complete metamorphism) or hemimetabolous (incomplete metamorphism) insects, but the term can be used to describe any developmental stage including pupa orimago (the adult, which does not molt in insects).
The number of instars an insect undergoes depends on the species and the environmental conditions. Lower temperatures and humidity often slow the rate of development. (Wikipedia)
A larva (plural larvae /ˈlɑrviː/) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
The larva’s appearance is generally very different from the adult form (e.g. caterpillars and butterflies). A larva often has unique structures and organs that do not occur in the adult form, while their diet might be considerably different. (Wikipedia)
Spiracles are openings on the surface of some animals that usually lead to respiratory systems. Insects and some more derived spiders have spiracles on their exoskeletons to allow air to enter the trachea. In the respiratory system of insects, the tracheal tubes primarily deliver oxygen directly into the animals’ tissues. The spiracles can be opened and closed in an efficient manner to reduce water loss. This is done by contracting closer muscles surrounding the spiracle. In order to open, the muscle relaxes. The closer muscle is controlled by the central nervous system but can also react to localized chemical stimuli. (Wikipedia)
Any of a group of spiral-shaped bacteria, some of which are serious pathogens for humans, causing such diseases as syphilis, yaws, Lyme disease, and relapsing fever. Spirochetes include the genera Spirochaeta, Treponema, Borrelia, and Leptospira.
Spirochetes are gram-negative, motile, spiral bacteria, from 3 to 500 micrometres long. Spirochetes are unique in that they have endocellular flagella (axial fibrils, or axial filaments), which number between 2 and more than 200 per organism, depending upon the species. Each axial fibril attaches at an opposite end and winds around the cell body, which is enclosed by an envelope. Spirochetes are characteristically found in a liquid environment (e.g., mud and water, blood and lymph).
Treponema includes the agents of syphilis (T. pallidum) and yaws (T. pertenue). Borrelia includes several species transmitted by lice and ticks and causing relapsing fever (B. recurrentis and others) and Lyme disease (B. burgdorferi) in humans. Spirochaeta are free-living, nonpathogenic inhabitants of mud and water, usually in oxygen-free regions.