The subphylum Chelicerata constitutes one of the major subdivisions of the phylum Arthropoda. It contains the sea spiders and several extinct lineages, such as the eurypterids; the Chelicerata originated as marine animals in the Middle Cambrian period. The surviving marine species include the four species of xiphosurans, the 1,300 species of pycnogonids, if the latter are indeed chelicerates. On the other hand, there are over 77,000 well-identified species of air-breathing chelicerates, there may be about 500,000 unidentified species. Like all arthropods, chelicerates have segmented bodies with jointed limbs, all covered in a cuticle made of chitin and proteins; the chelicerate bauplan consists of two tagmata, the prosoma and the opisthosoma, except that mites have lost a visible division between these sections. The chelicerae, which give the group its name, are the only appendages. In most sub-groups, they are modest pincers used to feed. However, spiders' chelicerae form fangs; the group has the open circulatory system typical of arthropods, in which a tube-like heart pumps blood through the hemocoel, the major body cavity.
Marine chelicerates have gills, while the air-breathing forms have both book lungs and tracheae. In general, the ganglia of living chelicerates' central nervous systems fuse into large masses in the cephalothorax, but there are wide variations and this fusion is limited in the Mesothelae, which are regarded as the oldest and most primitive group of spiders. Most chelicerates rely on modified bristles for touch and for information about vibrations, air currents, chemical changes in their environment; the most active hunting spiders have acute eyesight. Chelicerates were predators, but the group has diversified to use all the major feeding strategies: predation, herbivory and eating decaying organic matter. Although harvestmen can digest solid food, the guts of most modern chelicerates are too narrow for this, they liquidize their food by grinding it with their chelicerae and pedipalps and flooding it with digestive enzymes. To conserve water, air-breathing chelicerates excrete waste as solids that are removed from their blood by Malpighian tubules, structures that evolved independently in insects.
While the marine horseshoe crabs rely on external fertilization, air-breathing chelicerates use internal but indirect fertilization. Many species use elaborate courtship rituals to attract mates. Most lay eggs that hatch as what look like miniature adults, but all scorpions and a few species of mites keep the eggs inside their bodies until the young emerge. In most chelicerate species the young have to fend for themselves, but in scorpions and some species of spider the females protect and feed their young; the evolutionary origins of chelicerates from the early arthropods have been debated for decades. Although there is considerable agreement about the relationships between most chelicerate sub-groups, the inclusion of the Pycnogonida in this taxon has been questioned, the exact position of scorpions is still controversial, though they were long considered the most primitive of the arachnids. Venom has evolved three times in the chelicerates. In addition there have been undocumented descriptions of venom glands in Solifugae.
Chemical defense has been found in whip scorpions, shorttailed whipscorpions, beetle mites and sea spiders. Although the venom of a few spider and scorpion species can be dangerous to humans, medical researchers are investigating the use of these venoms for the treatment of disorders ranging from cancer to erectile dysfunction; the medical industry uses the blood of horseshoe crabs as a test for the presence of contaminant bacteria. Mites can cause allergies in humans, transmit several diseases to humans and their livestock, are serious agricultural pests; the Chelicerata are arthropods as they have: segmented bodies with jointed limbs, all covered in a cuticle made of chitin and proteins. Chelicerates' bodies consist of two tagmata, sets of segments that serve similar functions: the foremost one, called the prosoma or cephalothorax, the rear tagma is called the opisthosoma or abdomen. However, in the Acari there is no visible division between these sections; the prosoma is formed in the embryo by fusion of the acron, which carries the eyes, with segments two to seven, which all have paired appendages, while segment one is lost during the embryo's development.
Segment two has a pair of chelicerae, small appendages that form pincers, segment three has a pair of pedipalps that in most sub-groups perform sensory functions, while the remaining four cephalothorax segments have pairs of legs. In primitive forms the acron has a pair of compound eyes on the sides and four pigment-cup ocelli in the middle; the mouth is between segments three. The opisthosoma consists of twelve or fewer segments that formed two groups, a mesosoma of seven segments and a metasoma of five, terminating with a telson or spike; the abdominal appendages of modern chelicerates
Arachnids are a class of joint-legged invertebrate animals, in the subphylum Chelicerata. All adult 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, from the myth of the hubristic human weaver Arachne, turned into a spider. Spiders are the largest order in the class, which includes scorpions, mites and solifuges. In 2019, a molecular phylogenetic study placed horseshoe crabs in Arachnida. All extant arachnids are terrestrial, living on land. However, some inhabit freshwater environments and, with the exception of the pelagic zone, marine environments as well, they comprise over 100,000 named species. All adult arachnids have eight legs, arachnids may be distinguished from insects by this fact, since insects have six legs. However, arachnids have two further pairs of appendages that have become adapted for feeding and sensory perception.
The first pair, the chelicerae, serve in defense. The next pair of appendages, the pedipalps, have been adapted for feeding, and/or reproductive functions. In Solifugae, the palps are quite leg-like; the larvae of mites and Ricinulei have only six legs. However, mites are variable: as well as eight, there are adult mites with six or four legs. Arachnids are further distinguished from insects by the fact, their body is organized into two tagmata, called the prosoma, or cephalothorax, the opisthosoma, or abdomen. The cephalothorax is derived from the fusion of the cephalon and the thorax, is covered by a single, unsegmented carapace; the abdomen is segmented in the more primitive forms, but varying degrees of fusion between the segments occur in many groups. It is divided into a preabdomen and postabdomen, although this is only visible in scorpions, in some orders, such as the Acari, the abdominal sections are fused. A telson is present in scorpions, where it has been modified to a stinger, in the Schizomida, whip scorpions and Palpigradi.
Like all arthropods, arachnids have an exoskeleton, they have an internal structure of cartilage-like tissue, called the endosternite, to which certain muscle groups are attached. The endosternite is calcified in some Opiliones. Most arachnids lack extensor muscles in the distal joints of their appendages. Spiders and whipscorpions extend their limbs hydraulically using the pressure of their hemolymph. Solifuges and some harvestmen extend their knees by the use of elastic thickenings in the joint cuticle. Scorpions and some harvestmen have evolved muscles that extend two leg joints at once; the equivalent joints of the pedipalps of scorpions though, are extended by elastic recoil. There are characteristics that are important for the terrestrial lifestyle of arachnids, such as internal respiratory surfaces in the form of tracheae, or modification of the book gill into a book lung, an internal series of vascular lamellae used for gas exchange with the air. While the tracheae are individual systems of tubes, similar to those in insects, ricinuleids and some spiders possess sieve tracheae, in which several tubes arise in a bundle from a small chamber connected to the spiracle.
This type of tracheal system has certainly evolved from the book lungs, indicates that the tracheae of arachnids are not homologous with those of insects. Further adaptations to terrestrial life are appendages modified for more efficient locomotion on land, internal fertilisation, special sensory organs, water conservation enhanced by efficient excretory structures as well as a waxy layer covering the cuticle; the excretory glands of arachnids include up to four pairs of coxal glands along the side of the prosoma, one or two pairs of Malpighian tubules, emptying into the gut. Many arachnids have the other type of excretory gland, although several do have both; the primary nitrogenous waste product in arachnids is guanine. Arachnid blood is variable in composition, depending on the mode of respiration. Arachnids with an efficient tracheal system do not need to transport oxygen in the blood, may have a reduced circulatory system. In scorpions and some spiders, the blood contains haemocyanin, a copper-based pigment with a similar function to haemoglobin in vertebrates.
The heart is located in the forward part of the abdomen, may or may not be segmented. Some mites have no heart at all. Arachnids are carnivorous, feeding on the pre-digested bodies of insects and other small animals. Only in the harvestmen and among mites, such as the house dust mite, is there ingestion of solid food particles, thus exposure to internal parasites, although it is not unusual for spiders to eat their own silk. Several groups secrete venom from specialized glands to kill prey or enemies. Several mites and ticks are parasites. Arachnids produce digestive juices in their stomachs, use their pedipalps and chelicerae to pour them over their dead prey; the digestive juices turn the prey into a broth of nutrients, which the arachnid sucks into a pre-buccal cavity located in front of the mouth. Behind the mouth is a muscular, sclerotised pharynx, which acts as a pump, sucking the food through the mouth and on into the oesophagus and stomach. In some arachnids, the oesophagus a
An arthropod is an invertebrate animal having an exoskeleton, a segmented body, paired jointed appendages. Arthropods form the phylum Euarthropoda, which includes insects, arachnids and crustaceans; the term Arthropoda as proposed refers to a proposed grouping of Euarthropods and the phylum Onychophora. Arthropods are characterized by their jointed limbs and cuticle made of chitin mineralised with calcium carbonate; the arthropod body plan consists of each with a pair of appendages. The rigid cuticle inhibits growth, so arthropods replace it periodically by moulting. Arthopods are bilaterally symmetrical and their body possesses an external skeleton; some species have wings. Their versatility has enabled them to become the most species-rich members of all ecological guilds in most environments, they have over a million described species, making up more than 80 per cent of all described living animal species, some of which, unlike most other animals, are successful in dry environments. Arthropods range in size from the microscopic crustacean Stygotantulus up to the Japanese spider crab.
Arthropods' primary internal cavity is a haemocoel, which accommodates their internal organs, through which their haemolymph – analogue of blood – circulates. Like their exteriors, the internal organs of arthropods are built of repeated segments, their nervous system is "ladder-like", with paired ventral nerve cords running through all segments and forming paired ganglia in each segment. Their heads are formed by fusion of varying numbers of segments, their brains are formed by fusion of the ganglia of these segments and encircle the esophagus; the respiratory and excretory systems of arthropods vary, depending as much on their environment as on the subphylum to which they belong. Their vision relies on various combinations of compound eyes and pigment-pit ocelli: in most species the ocelli can only detect the direction from which light is coming, the compound eyes are the main source of information, but the main eyes of spiders are ocelli that can form images and, in a few cases, can swivel to track prey.
Arthropods have a wide range of chemical and mechanical sensors based on modifications of the many setae that project through their cuticles. Arthropods' methods of reproduction and development are diverse; the evolutionary ancestry of arthropods dates back to the Cambrian period. The group is regarded as monophyletic, many analyses support the placement of arthropods with cycloneuralians in a superphylum Ecdysozoa. Overall, the basal relationships of Metazoa are not yet well resolved; the relationships between various arthropod groups are still debated. Aquatic species use either external fertilization. All arthropods lay eggs, but scorpions give birth to live young after the eggs have hatched inside the mother. Arthropod hatchlings vary from miniature adults to grubs and caterpillars that lack jointed limbs and undergo a total metamorphosis to produce the adult form; the level of maternal care for hatchlings varies from nonexistent to the prolonged care provided by scorpions. Arthropods contribute to the human food supply both directly as food, more indirectly as pollinators of crops.
Some species are known to spread severe disease to humans and crops. The word arthropod comes from the Greek ἄρθρον árthron, "joint", πούς pous, i.e. "foot" or "leg", which together mean "jointed leg". Arthropods are invertebrates with jointed limbs; the exoskeleton or cuticles consists of a polymer of glucosamine. The cuticle of many crustaceans, beetle mites, millipedes is biomineralized with calcium carbonate. Calcification of the endosternite, an internal structure used for muscle attachments occur in some opiliones. Estimates of the number of arthropod species vary between 1,170,000 and 5 to 10 million and account for over 80 per cent of all known living animal species; the number of species remains difficult to determine. This is due to the census modeling assumptions projected onto other regions in order to scale up from counts at specific locations applied to the whole world. A study in 1992 estimated that there were 500,000 species of animals and plants in Costa Rica alone, of which 365,000 were arthropods.
They are important members of marine, freshwater and air ecosystems, are one of only two major animal groups that have adapted to life in dry environments. One arthropod sub-group, insects, is the most species-rich member of all ecological guilds in land and freshwater environments; the lightest insects weigh less than 25 micrograms. Some living crustaceans are much larger; the embryos of all arthropods are segmented, built from a series of repeated modules. The last common ancestor of living arthropods consisted of a series of undifferentiated segments, each with a pair of appendages that functioned as limbs. However, all known living and fossil arthropods have grouped segments into tagmata in which segments and their limbs are specialized in various ways; the three-
Animals are multicellular eukaryotic organisms that form the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, grow from a hollow sphere of cells, the blastula, during embryonic development. Over 1.5 million living animal species have been described—of which around 1 million are insects—but it has been estimated there are over 7 million animal species in total. Animals range in length from 8.5 millionths of a metre to 33.6 metres and have complex interactions with each other and their environments, forming intricate food webs. The category includes humans, but in colloquial use the term animal refers only to non-human animals; the study of non-human animals is known as zoology. Most living animal species are in the Bilateria, a clade whose members have a bilaterally symmetric body plan; the Bilateria include the protostomes—in which many groups of invertebrates are found, such as nematodes and molluscs—and the deuterostomes, containing the echinoderms and chordates.
Life forms interpreted. Many modern animal phyla became established in the fossil record as marine species during the Cambrian explosion which began around 542 million years ago. 6,331 groups of genes common to all living animals have been identified. Aristotle divided animals into those with those without. Carl Linnaeus created the first hierarchical biological classification for animals in 1758 with his Systema Naturae, which Jean-Baptiste Lamarck expanded into 14 phyla by 1809. In 1874, Ernst Haeckel divided the animal kingdom into the multicellular Metazoa and the Protozoa, single-celled organisms no longer considered animals. In modern times, the biological classification of animals relies on advanced techniques, such as molecular phylogenetics, which are effective at demonstrating the evolutionary relationships between animal taxa. Humans make use of many other animal species for food, including meat and eggs. Dogs have been used in hunting, while many aquatic animals are hunted for sport.
Non-human animals have appeared in art from the earliest times and are featured in mythology and religion. The word "animal" comes from the Latin animalis, having soul or living being; the biological definition includes all members of the kingdom Animalia. In colloquial usage, as a consequence of anthropocentrism, the term animal is sometimes used nonscientifically to refer only to non-human animals. Animals have several characteristics. Animals are eukaryotic and multicellular, unlike bacteria, which are prokaryotic, unlike protists, which are eukaryotic but unicellular. Unlike plants and algae, which produce their own nutrients animals are heterotrophic, feeding on organic material and digesting it internally. With few exceptions, animals breathe oxygen and respire aerobically. All animals are motile during at least part of their life cycle, but some animals, such as sponges, corals and barnacles become sessile; the blastula is a stage in embryonic development, unique to most animals, allowing cells to be differentiated into specialised tissues and organs.
All animals are composed of cells, surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins. During development, the animal extracellular matrix forms a flexible framework upon which cells can move about and be reorganised, making the formation of complex structures possible; this may be calcified, forming structures such as shells and spicules. In contrast, the cells of other multicellular organisms are held in place by cell walls, so develop by progressive growth. Animal cells uniquely possess the cell junctions called tight junctions, gap junctions, desmosomes. With few exceptions—in particular, the sponges and placozoans—animal bodies are differentiated into tissues; these include muscles, which enable locomotion, nerve tissues, which transmit signals and coordinate the body. There is an internal digestive chamber with either one opening or two openings. Nearly all animals make use of some form of sexual reproduction, they produce haploid gametes by meiosis.
These fuse to form zygotes, which develop via mitosis into a hollow sphere, called a blastula. In sponges, blastula larvae swim to a new location, attach to the seabed, develop into a new sponge. In most other groups, the blastula undergoes more complicated rearrangement, it first invaginates to form a gastrula with a digestive chamber and two separate germ layers, an external ectoderm and an internal endoderm. In most cases, a third germ layer, the mesoderm develops between them; these germ layers differentiate to form tissues and organs. Repeated instances of mating with a close relative during sexual reproduction leads to inbreeding depression within a population due to the increased prevalence of harmful recessive traits. Animals have evolved numerous mechanisms for avoiding close inbreeding. In some species, such as the splendid fairywren, females benefit by mating with multiple males, thus producing more offspring of higher genetic quality; some animals are capable of asexual reproduction, which results
Cannibalism involves consuming all or part of another individual of the same species as food. To consume the same species, or show cannibalistic behavior, is a common ecological interaction in the animal kingdom, has been recorded in more than 1,500 species. Human cannibalism is well-documented, both in recent times; the rate of cannibalism increases in nutritionally-poor environments as individuals turn to other conspecific individuals as an additional food-source. Cannibalism regulates population numbers, whereby resources such as food and territory become more available with the decrease of potential competition. Although it may benefit the individual, it has been shown that the presence of cannibalism decreases the expected survival rate of the whole population and increases the risk of consuming a relative. Other negative effects may include the increased risk of pathogen transmission as the encounter rate of hosts increases. Cannibalism, does not—as once believed—occur only as a result of extreme food shortage or of artificial/unnatural conditions, but may occur under natural conditions in a variety of species.
Cannibalism seems prevalent in aquatic ecosystems, in which up to 90% of the organisms engage in cannibalistic activity at some point in their life-cycle. Cannibalism is not restricted to carnivorous species: it occurs in herbivores and in detritivores. Sexual cannibalism involves the consumption of the male by the female individual before, during or after copulation. Other forms of cannibalism include intrauterine cannibalism. Behavioural and morphological adaptations have evolved to decrease the rate of cannibalism in individual species. In environments where food availability is constrained, individuals can receive extra nutrition and energy if they use other conspecific individuals as an additional food source; this would, in turn, increase the survival rate of the cannibal and thus provide an evolutionary advantage in environments where food is scarce. A study conducted on wood frog tadpoles showed that those that exhibited cannibalistic tendencies had faster growth rates and higher fitness levels than non-cannibals.
An increase of size and growth would give them the added benefit of protection from potential predators such as other cannibals and give them an advantage when competing for resources The nutritional benefits of cannibalism may allow for the more efficient conversion of a conspecific diet into reusable resources than herbaceous diet. This facilitates for faster development. Studies have shown that there is a noticeable size difference between animals fed on a high conspecific diet which were smaller compared to those fed on a low conspecific diet. Hence, individual fitness could only be increased if the balance between developmental rate and size is balanced out, with studies showing that this is achieved in low conspecific diets. Cannibalism regulates population numbers and benefits the cannibalistic individual and its kin as resources such as extra shelter and food are freed. However, this is only the case if the cannibal recognizes its own kin as this won't hinder any future chances of perpetuating its genes in future generations.
The elimination of competition can increase mating opportunities, allowing further spread of an individual's genes. Animals which have diets consisting of predominantly conspecific prey expose themselves to a greater risk of injury and expend more energy foraging for suitable prey as compared to non-cannibalistic species. In order to combat the risk of personal injury, a predator targets younger or more vulnerable prey. However, the time necessitated by such selective predation could result in a failure to meet the predator's self-set nutritional requirements. In addition, the consumption of conspecific prey may involve the ingestion of defense compounds and hormones, which have the capacity to impact the developmental growth of the cannibal's offspring Hence, predators partake in a cannibalistic diet in conditions where alternative food sources are absent or not as available. Failure to recognize kin prey is a disadvantage, provided cannibals target and consume younger individuals. For example, a male stickleback fish may mistake their own "eggs" for their competitor's eggs, hence would inadvertently eliminate some of its own genes from the available gene pool.
Kin recognition has been observed in tadpoles of the spadefoot toad, whereby cannibalistic tadpoles of the same clutch tended to avoid consuming and harming siblings, while eating other non-siblings. The act of cannibalism may facilitate trophic disease transmission within a population, though cannibalistically spread pathogens and parasites employ alternative modes of infection. Cannibalism can reduce the prevalence of parasites in the population by decreasing the number of susceptible hosts and indirectly killing the parasite in the host, it has been shown in some studies that the risk of encountering an infected victim increases when there is a higher cannibalism rate, though this risk drops as the number of available hosts decreases. However, this is only the case. Cannibalism is an ineffective method of disease spread as cannibalism in the animal kingdom is a one-on-one interaction, the spread of disease requires group cannibalism.
The Scorpionidae make up the superfamily Scorpionoidea. The family was established by Pierre André Latreille, 1802. According to The Scorpion Files and Prendini & Francke: Scorpioninae Latreille, 1802 Heterometrus Ehrenberg, 1828 Opistophthalmus Koch, 1837 Pandinus Thorell, 1876 Scorpio Linnaeus, 1758 †Mioscorpio Kjellesvig-Waering, 1986 †Sinoscorpius Hong, 1983 Diplocentrinae Karsch, 1880 Diplocentrini Karsch, 1880 Bioculus Stahnke, 1968 Cazierius Francke, 1978 Cryptoiclus Teruel & Kovařík, 2012 Didymocentrus Kraepelin, 1905 Diplocentrus Peters, 1861D. Peloncillensis D. spitzeri Heteronebo Pocock, 1899 Oiclus Simon, 1880 Tarsoporosus Francke, 1978 Nebini Kraepelin, 1905 Nebo Simon, 1878 Rugodentinae Bastawade, Sureshan & Radhakrishnan, 2005 Rugodentus Bastawade, Sureshan & Radhakrishnan, 2005 Urodacinae Pocock, 1893 Urodacus Peters, 1861 Aops Volschenk & Prendini, 2008
Binomial nomenclature called binominal nomenclature or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, although they can be based on words from other languages. Such a name is called a binomen, binominal name or a scientific name; the first part of the name – the generic name – identifies the genus to which the species belongs, while the second part – the specific name or specific epithet – identifies the species within the genus. For example, humans belong within this genus to the species Homo sapiens. Tyrannosaurus rex is the most known binomial; the formal introduction of this system of naming species is credited to Carl Linnaeus beginning with his work Species Plantarum in 1753. But Gaspard Bauhin, in as early as 1623, had introduced in his book Pinax theatri botanici many names of genera that were adopted by Linnaeus; the application of binomial nomenclature is now governed by various internationally agreed codes of rules, of which the two most important are the International Code of Zoological Nomenclature for animals and the International Code of Nomenclature for algae and plants.
Although the general principles underlying binomial nomenclature are common to these two codes, there are some differences, both in the terminology they use and in their precise rules. In modern usage, the first letter of the first part of the name, the genus, is always capitalized in writing, while that of the second part is not when derived from a proper noun such as the name of a person or place. Both parts are italicized when a binomial name occurs in normal text, thus the binomial name of the annual phlox is now written as Phlox drummondii. In scientific works, the authority for a binomial name is given, at least when it is first mentioned, the date of publication may be specified. In zoology "Patella vulgata Linnaeus, 1758"; the name "Linnaeus" tells the reader who it was that first published a description and name for this species of limpet. "Passer domesticus". The original name given by Linnaeus was Fringilla domestica; the ICZN does not require that the name of the person who changed the genus be given, nor the date on which the change was made, although nomenclatorial catalogs include such information.
In botany "Amaranthus retroflexus L." – "L." is the standard abbreviation used in botany for "Linnaeus". "Hyacinthoides italica Rothm. – Linnaeus first named this bluebell species Scilla italica. The name is composed of two word-forming elements: "bi", a Latin prefix for two, "-nomial", relating to a term or terms; the word "binomium" was used in Medieval Latin to mean a two-term expression in mathematics. Prior to the adoption of the modern binomial system of naming species, a scientific name consisted of a generic name combined with a specific name, from one to several words long. Together they formed a system of polynomial nomenclature; these names had two separate functions. First, to designate or label the species, second, to be a diagnosis or description. In a simple genus, containing only two species, it was easy to tell them apart with a one-word genus and a one-word specific name; such "polynomial names" may sometimes look like binomials, but are different. For example, Gerard's herbal describes various kinds of spiderwort: "The first is called Phalangium ramosum, Branched Spiderwort.
The other... is aptly termed Phalangium Ephemerum Virginianum, Soon-Fading Spiderwort of Virginia". The Latin phrases are short descriptions, rather than identifying labels; the Bauhins, in particular Caspar Bauhin, took some important steps towards the binomial system, by pruning the Latin descriptions, in many cases to two words. The adoption by biologists of a system of binomial nomenclature is due to Swedish botanist and physician Carl von Linné, more known by his Latinized name Carl Linnaeus, it was in his 1753 Species Plantarum that he first began using a one-word "trivial name" together with a generic name in a system of binomial nomenclature. This trivial name is what is now known as specific name; the Bauhins' genus names were retained in many of these, but the descriptive part was reduced to a single word. Linnaeus's trivial names introduced an important new idea, namely that the function of a name could be to give a species a unique label; this meant. Thus Gerard's Phalangium ephemerum virginianum became Tradescantia virgi