Arthropod exoskeletons are made of cuticle, a non-cellular material secreted by the epidermis. Their cuticles vary in the details of their structure, but generally consist of three main layers: the epicuticle, a thin outer waxy coat that moisture-proofs the other layers and gives them some protection; the exocuticle, which consists of chitin and chemically hardened proteins; and the ...
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 ...
Arthropod cuticle is a biological composite material, consisting of two main portions: fibrous chains of alpha-chitin within a matrix of silk-like and globular proteins, of which the best-known is the rubbery protein called resilin. The relative abundance of these two main components varies from approximately 50/50 to 80/20 chitin protein, with ...
- Eyes and functions
- Genetic controls
Apposition eyes are the most common form of eye, and are presumably the ancestral form of compound eye. They are found in all arthropod groups, although they may have evolved more than once within this phylum. Some annelids and bivalves also have apposition eyes. They are also possessed by Limulus, the horseshoe crab, and there are suggestions that other chelicerates developed their simple eyes by reduction from a compound starting point. Some caterpillars appear to have evolved compound eyes fr
Most arthropods have at least one of two types of eye: lateral compound eyes, and smaller median ocelli, which are simple eyes. When both are present, the two eye types are used in concert because each has its own advantage. Some insect larvae, e.g., caterpillars, have a different type of simple eye known as stemmata. These eyes usually provide only a rough image, but they can possess resolving powers of 4 degrees of arc, be polarization sensitive and capable of increasing their absolute sensiti
The head patterning is controlled by orthodenticle, a homeobox gene which demarcates the segments from the top-middle of the head to the more lateral aspects. The ocelli are in an orthodenticle-rich area, and the gene is not expressed by the time one gets as lateral as the compound eyes. The gene dachshund is involved in the development of the compound eye. Different opsins are used in the ocelli of compound eyes.
Hexapods are currently thought to fall within the Crustacean crown group; while molecular work paved the way for this association, their eye morphology and development is also markedly similar. The eyes are strikingly different from the myriapods, which were traditionally considered to be a sister group to the Hexapoda. Both ocelli and compound eyes were probably present in the last common arthropod ancestor, and may be apomorphic with ocelli in other phyla, such as the annelids. Median ocelli a
- Biramous and uniramous
The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments are of Latin origin, and may be confused with terms for bones: coxa, trochanter, femur, tibia, tarsus, ischium, metatarsus, carpus, dactylus, patella. Homologies of leg segments between groups are difficult to prove and are the source of much argument. Some authors posit up to eleven segments per leg for the most recent common ancestor of extant arthropods b
The appendages of arthropods may be either biramous or uniramous. A uniramous limb comprises a single series of segments attached end-to-end. A biramous limb, however, branches into two, and each branch consists of a series of segments attached end-to-end.
Arachnid legs differ from those of insects by the addition of two segments on either side of the tibia, the patella between the femur and the tibia, and the metatarsus between the tibia and the tarsus, making a total of seven segments.
The legs of crustaceans are divided primitively into seven segments, which do not follow the naming system used in the other groups. They are: coxa, basis, ischium, merus, carpus, propodus, and dactylus. In some groups, some of the limb segments may be fused together. The claw of a lobster or crab is formed by the articulation of the dactylus against an outgrowth of the propodus. Crustacean limbs also differ in being biramous, whereas all other extant arthropods have uniramous limbs.
Myriapods have seven-segmented walking legs, comprising coxa, trochanter, prefemur, femur, tibia, tarsus, and a tarsal claw. Myriapod legs show a variety of modifications in different groups. In all centipedes, the first pair of legs is modified into a pair of venomous fangs called forcipules. In most millipedes, one or two pairs of walking legs in adult males are modified into sperm-transferring structures called gonopods. In some millipedes, the first leg pair in males may be reduced to tiny h
Insects and their relatives are hexapods, having six legs, connected to the thorax, each with five components. In order from the body they are the coxa, trochanter, femur, tibia, and tarsus. Each is a single segment, except the tarsus which can be from three to seven segments, each referred to as a tarsomere.
The aim of this WikiProject is to set out broad suggestions about how to organize data in the articles relating to insects, arachnids, crustaceans and other arthropods.We also hope to encourage the development of important stubs and articles following these suggestions.
Arthropoda is the phylum for aw the Arthropod speshie. Arthropoda is in the domain eukaryots, the kinrick Animalia, the subkinrick Eumetazoa, an the superphylum Ecdysozoa. Arthropods haes exoskelets, lithed bodies, an lithed limms. Some o the maist weel-kent arthropods is insects, speeders, an trilobytes. Subphylum Trilobitomorpha
Arthropod heads are typically fused capsules that bear a variety of complex structures such as the eyes, antennae and mouth parts. The challenge that the arthropod head problem has to address is to what extent the various structures of the arthropod head can be resolved into a set of hypothetical ancestral segments.
Aug 24, 2020 · Hamilton, A.J. et al. 2013: Estimating global arthropod species richness: refining probabilistic models using probability bounds analysis. Oecologia , 171(2): 357–365. DOI : 10.1007/s00442-012-2434-5
A consensus emerged from about 2010 onwards, based on both morphological and molecular evidence. Extant (living) arthropods are a monophyletic group and are divided into three main clades: chelicerates (including arachnids), pancrustaceans (the paraphyletic crustaceans plus insects and their allies), and myriapods (centipedes, millipedes and ...