Arachnid | Definition, Facts, & Examples | Britannica
2024年11月21日 · Arachnid, any member of the arthropod group that includes spiders, daddy longlegs, scorpions, and mites and ticks, as well as lesser-known subgroups. Some arachnids transmit diseases to humans and plants. Learn more about the physical features, behavior, natural history, and evolution of arachnids.
Anatomy of arachnids | Britannica
arachnid , Any member of the class Arachnida, primarily carnivorous arthropods having a well-developed head, a hard external skeleton, and four pairs of walking legs. Spiders and scorpions have a segmented body, but daddy longlegs, ticks, and mites do not.Arachnids range in size from tiny mites (0.003 in. [0.08 mm] long) to the 8-in. (21-cm) black scorpion of Africa.
Arachnid - Predators, Habitats, Adaptations | Britannica
2024年11月21日 · Arachnid - Predators, Habitats, Adaptations: Most arachnids are free-living terrestrial forms, but some are parasitic and aquatic. Usually not great travelers, arachnids may rely on ballooning or phoresy to cover long distances. Most arachnids are solitary predators, feeding chiefly on smaller arthropods. The arachnid body has two parts, the cephalothorax …
Arachnoid mater | anatomy | Britannica
Other articles where arachnoid mater is discussed: epidural hematoma: Anatomy: The second layer, the arachnoid mater, covers the brain and pia mater but does not follow the contour of the involutions of the brain. The outermost layer, the dura mater, provides a …
Arachnid - Evolution, Paleontology, Classification | Britannica
2024年11月21日 · Arachnid - Evolution, Paleontology, Classification: A major characteristic of arachnid evolution is that segments were fused or lost. In general, scorpions have the most primitive features, and spiders and mites are the most highly evolved. The earliest forms recognizable as arachnids include a scorpion from the Silurian. Class Arachnida have …
Arachnids Portal | Britannica
When it comes to creepy-crawlies, arachnids are some of the first critters that might come to mind. This arthropod group includes spiders, daddy longlegs, and scorpions, among other creatures that many...
Arachnoid trabeculae | anatomy | Britannica
Other articles where arachnoid trabeculae is discussed: meninges: …number of fine filaments called arachnoid trabeculae pass from the arachnoid through the subarachnoid space to blend with the tissue of the pia mater. The arachnoid trabeculae are embryologic remnants of the common origin of the arachnoid and pia mater, and they have the frail structure characteristic …
Arachnoid villa | anatomy | Britannica
Other articles where arachnoid villa is discussed: meninges: …processes of the arachnoid, called arachnoid villi or arachnoid granulations, are involved in the passage of cerebrospinal fluid from the subarachnoid space to the dural sinuses. Spinal anesthetics are often introduced into the subarachnoid space.
insect - Students | Britannica Kids | Homework Help
Encyclopædia Britannica, Inc. Despite their diversity, all adult insects share some basic external and internal anatomical features. Insects are distinguished from other members of the animal kingdom by having six legs; one pair of antennae; a ringed, or segmented, body; and three well-defined body regions.