All adult arachnids have four pairs of legs, and arachnids may be easily distinguished from insects by this fact, since insects have three pairs of legs. However, arachnids also have two further pairs of appendages that have become adapted for feeding, defense, and sensory perception. The first pair, the chelicerae, serve in feeding and defense. The next pair of appendages, the pedipalps have been adapted for feeding, locomotion, and/or reproductive functions.
Like all arthropods, arachnids have an exoskeleton. They also have an internal structure of cartilage-like tissue, to which certain muscle groups are attached.
Arachnids have no antennae or wings. Their body is organized into two parts: the cephalothorax, and the abdomen.
There are some adaptations for life on land. They have internal respiratory surfaces. These may be trachea (tubes), or a modification of gills into a 'book lung'. This is an internal series of lamellae used for gas exchange with the air.
Arachnids are mostly carnivorous, feeding on the pre-digested bodies of insects and other small animals. Only the harvestmen and some mites eat solid food particles. Predigestion avoids exposure to internal parasites. Several groups secrete venom from specialized glands to kill prey or enemies. Several mites are external parasites, and some of them are carriers of disease (vectors).
Arachnids pour digestive juices produced in their stomachs over their prey after killing it with their pedipalps and chelicerae. The digestive juices rapidly turn the prey into a broth of nutrients which the arachnid sucks into a pre-buccal cavity located immediately in front of the mouth. Behind the mouth is a muscular, pharynx, which acts as a pump, sucking the food through the mouth and on into the oesophagus and stomach. In some arachnids, the oesophagus also acts as an additional pump.
The word "Arachnida" comes from the Greek for 'spider'. In legend, a girl called Arachne was turned into a spider by the goddess Athena. Arachne said she'd win a weaving contest against the goddess. Athena won, but Arachne became angry, and started to weave an insult to the gods. Then Athena turned her into a spider for her disrespect.
The subdivisions of the arachnids are usually treated as orders. Historically, mites and ticks were treated as a single order, Acari. However, molecular phylogenetic studies suggest that the two groups do not form a single clade; morphological similarities are probably due to convergence. They are now usually treated as two separate taxa – Acariformes, mites, and Parasitiformes, ticks – which may be ranked as orders or superorders. The arachnid subdivisions are listed below alphabetically; numbers of species are approximate.
It is estimated that 98,000 arachnid species have been described, and that there may be up to 600,000 in total.
Arthropod
Arthropods (Greek language for "joint-legged") are a large group of invertebrate animals. Insects, spiders, crabs, shrimp, millipedes, and centipedes are all arthropods. In the scientific classification, all arthropods are members of the phylum Arthropoda. Arthropods have segmented body, an exoskeleton and legs with joints. Most arthropods live on land, but some live in water. Arthropods have by far the greatest number of species of any animal group. Arthropods are a source of food for many animals, including humans.
Scientists know of more than 1 million species of arthropods. 80% of all known animal species are arthropods. Many more species have not yet been described.
Most arthropod species are insects. "Insects are the most diverse organisms in the history of life".
Most arthropods live on land. The phylum Arthropoda is the only phylum of invertebrates that mostly live on land. But crustaceans (crabs, shrimp and their relatives) mostly live in water.
Arthropods are also the first phylum to develop genuine flight.
Arthropods have a hard exoskeleton. The exoskeleton reduces the loss of water (dessication). This helps them to live on land without drying out.
Arthropods are made up of four groups of living animals and one group of extinct animals:
University of Alabama
The University of Alabama (UA) is a university in the U.S. state of Alabama. The University of Alabama is in the city of Tuscaloosa. People can usually just say "Alabama" or "UA" for short when they are talking about the University.
UA opened in 1831 and now about 35,000 students study there. UA is one of the three largest universities in Alabama. Auburn University and University of Alabama at Birmingham are the other two main schools in Alabama. Students study many things at UA, such as liberal arts, science, engineering, communication, engineering, education, social work, nursing, human sciences (such as fashion design) and law. People study to get bachelor's degrees, Master's degrees and doctorates at Alabama. Also, graduates can get an Education Specialist degree.
Many people have heard about the University of Alabama because it has many good sports teams. These sports teams are called the Crimson Tide. The football team from UA has won the national football championship 12 times in the past 83 years and play at Bryant–Denny Stadium.
In 1963, Alabama Gov. George Wallace announced in his inaugural address, "segregation now, segregation tomorrow, segregation forever" as his policy. He personally blocked the door to Foster Auditorium at the University of Alabama to prevent the enrollment of two black students. He moved aside only when confronted by General Henry Graham of the Alabama National Guard, who was ordered by President John F. Kennedy to intervene.
Buttercup
Buttercups are a large genus of flowering plants called Ranunculus. It has yellow, shiny petals, and grows wild in many places. It is poisonous to eat for humans and cattle, but when dry the poison is not active.
There are about 200 to 600 species in this one genus. They mostly have yellow or sometimes white flowers. Buttercups include a wide variety of flower types, grouped by a plant naming system in the genus "Ranunculus". Among them are the Meadow Buttercup ("Ranunculus acris"), Goldilocks Buttercup ("R. auricomus"), Creeping Buttercup ("R. repens"), Large White Buttercup ("R. platanifolius"), Celery-leaved Buttercup ("R. sceleratus"), Corn Buttercup ("R. arvensis"), Bulbous Buttercup ("R. bulbosus") and Glacial Buttercup ("R. glacialis").
Lesser Celandine ("R. ficaria"), Lesser Spearwort ("R. flammula"), and Greater Spearwort ("R. lingua") also belong to the buttercup family.
Plants of the commonly named buttercup family grow in many different variations but most can be identified by their yellow cupped flowers and free-growing habit. The plants often climb or sprawl, with leaves arranged in spirals. Some may contain leaves without stipules and flowers with many stamens.
Molecular investigation of the genus shows that "Ranunculus" is not monophyletic. Proposals are under way to split up the genus.
Highlights shining on the reflective petals of the buttercup can be seen in the images at left and above.
People sometimes hold a fresh buttercup flower under the chin of a friend or family member. If a yellow reflection from the flower's shiny petals can be seen under the chin, the person is said to "like butter". This custom is still taught to young children and shows how buttercup petals reflect light.
Some other plants and people are named buttercup, based on the name of the yellow wild flower. These include a type of pumpkin, and the girl's name Buttercup.
""Build Me Up Buttercup"" was the name of a popular song by The Foundations during the 1960s. A song called ""Buttercup"" was released by Jack Stauber in 2017. A cartoon character from television series was also named Buttercup. Buttercups and their poisonous effect are used as a theme in the "PC game Undertale."