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-
Darkling beetle is the common name of the large family of beetles, Tenebrionidae. The number of species in the Tenebrionidae is estimated at more than 20,000 and the family is cosmopolitan in distribution. Tenebrio is the Latin generic name that Carl Linnaeus assigned to some flour beetles in his 10th edition of Systema Naturae 1758-59.. The word means "seeker of dark places". Numerous Tenebrionidae species do inhabit dark places, there are many species in genera such as Stenocara and Onymacris, which are active by day and inactive at night; the family covers a varied range of forms, such that classification presents great difficulties. The following list of subfamilies was accepted in 2005. Alleculinae Laporte, 1840 Cossyphodinae Wasmann, 1899 Diaperinae Latreille, 1802 Lagriinae Latreille, 1825 Nilioninae Lacordaire, 1859 Phrenapatinae Solier, 1834 Pimeliinae Latreille, 1802 Stenochiinae Kirby, 1837 Tenebrioninae Latreille, 1802 Zolodininae Watt, 1974Ongoing phylogenetic studies are showing that some taxonomic changes are needed.
For instance the tribal classification of tribe Pedinini has been altered. The misspelling "Terebrionidae" occurs enough to be overlooked; the error appears to have no particular significance, but to be the product of misreadings, mis-scans and mis-typings. The Tenebrionidae may be identified by a combination of features, including: Their 11-segmented antennae that may be filiform, moniliform or weakly clubbed First abdominal sternite is entire and not divided by the hind coxae Eyes notched by a frontal ridge The tarsi have four segments in the hind pair and five in the fore and mid legs, tarsal claws are simple Tenebrionid beetles occupy ecological niches in deserts and forests as plant scavengers. Most species are generalistic omnivores, feed on decaying leaves, rotting wood, fresh plant matter, dead insects, fungi as larvae and adults. Several genera, including Bolitotherus, are specialized fungivores. Many of the larger species are flightless, those that are capable, such as T. molitor, only do so when necessary, such as when dispersing or malnourished.
The larvae, known as mealworms or false wireworms, are fossorial armored and nocturnal. They may be an important resource for certain invertebrates and small mammals. However, the adults of many species have chemical defenses and are protected against predators. Adults of most species, except grain pests, have slow metabolisms, live long lives compared to other insects, ranging from six months to two years; some species live in intensely dry deserts such as the Namib, have evolved adaptions by which they collect droplets of fog that deposit on their elytra. As the droplets accumulate the water drains down the beetles' backs to their mouthparts, where they swallow it. Humans spread some species such that they have become cosmopolitan, such as Tribolium castaneum, the red flour beetle, spread through grain products; the larval stages of several species are cultured as feeder insects for captive insectivores or as laboratory subjects: Tenebrio molitor is used to feed terrestrial amniotes kept in terraria.
Tribolium castaneum is a laboratory animal useful as a model organism in studies of intragenomic conflict and population ecology. Zophobas morio, or superworm, is valued as a feed for captive reptiles. Alphitobius diaperinus, lesser mealworm Many tenebrionids are pests of cereal and flour silos and other storage facilities, including T. castaneum, other Tribolium species such as Tribolium confusum and Tribolium destructor, Gnathocerus cornutus. In southwestern North America, species of the genus Eleodes are well known as "pinacate beetles" or "desert stink beetles". Several genera, such as Stenocara and Onymacris, are of interest in ecological studies of arid conditions and their associated adaptations. Ulomoides dermestoides, known as "chinese weevil", "peanut beetle", "cancer beetle", or "asthma beetle", is eaten in Argentina where it is thought to be a treatment for cancer and other illnesses. Tenebrionidae.net- information and pictures about darkling beetles
Caelus or Coelus was a primal god of the sky in Roman myth and theology and literature. The deity's name appears in masculine grammatical form when he is conceived of as a male generative force, but the neuter form Caelum is found as a divine personification; the name of Caelus indicates that he was the Roman counterpart of the Greek god Uranus, of major importance in the theogonies of the Greeks. Varro couples him with Terra as pater and mater, says that they are "great deities" in the theology of the mysteries at Samothrace. Although Caelus is not known to have had a cult at Rome, not all scholars consider him a Greek import given a Latin name. Vitruvius includes him among celestial gods; as a sky god, he became identified with Jupiter, as indicated by an inscription that reads Optimus Maximus Caelus Aeternus Iup<pi>ter. According to Cicero and Hyginus, Caelus Dies. Caelus and Dies were in this tradition the parents of Mercury. With Trivia, Caelus was the father of the distinctively Roman god Janus, as well as of Saturn and Ops.
Caelus was the father of one of the three forms of Jupiter, the other two fathers being Aether and Saturn. In one tradition, Caelus was the father with Tellus of the Muses, though was this a mere translation of Ouranos from a Greek source. Caelus substituted for Uranus in Latin versions of the myth of Saturn castrating his heavenly father, from whose severed genitals, cast upon the sea, the goddess Venus was born. In his work On the Nature of the Gods, Cicero presents a Stoic allegory of the myth in which the castration signifies "that the highest heavenly aether, that seed-fire which generates all things, did not require the equivalent of human genitals to proceed in its generative work." For Macrobius, the severing marks off Chaos from fixed and measured Time as determined by the revolving Heavens. The semina rerum are the elements which create the world; the divine spatial abstraction Caelum is a synonym for Olympus as a metaphorical heavenly abode of the divine, both identified with and distinguished from the mountain in ancient Greece named as the home of the gods.
Varro says that the Greeks call Caelum "Olympus." As a representation of space, Caelum is one of the components of the mundus, the "world" or cosmos, along with terra and aer. In his work on the cosmological systems of antiquity, the Dutch Renaissance humanist Gerardus Vossius deals extensively with Caelus and his duality as both a god and a place that the other gods inhabit; the ante-Nicene Christian writer Lactantius uses the Latin theonyms Caelus and Jupiter to refer to the three divine hypostases of the Neoplatonic school of Plotinus: the First God and Soul, son of the Intelligible. It is though not universally agreed that Caelus is depicted on the cuirass of the Augustus of Prima Porta, at the top above the four horses of the Sun god's quadriga, he is a mature, bearded man who holds a cloak over his head so that it billows in the form of an arch, a conventional sign of deity that "recalls the vault of the firmament." He is paired with the personification of Earth at the bottom of the cuirass.
On an altar of the Lares now held by the Vatican, Caelus in his chariot appears along with Apollo-Sol above the figure of Augustus. As Caelus Nocturnus, he was the god of the starry sky. In a passage from Plautus, Nocturnus is regarded as the opposite of the Sun god. Nocturnus appears in several inscriptions found in Dalmatia and Italy, in the company of other deities who are found in the cosmological schema of Martianus Capella, based on the Etruscan tradition. In the Etruscan discipline of divination, Caelus Nocturnus was placed in the sunless north opposite Sol to represent the polar extremities of the axis; this alignment was fundamental to the drawing of a templum for the practice of augury. The name Caelus occurs in dedicatory inscriptions in connection to the cult of Mithras; the Mithraic deity Caelus is sometimes depicted allegorically as an eagle bending over the sphere of heaven marked with symbols of the planets or the zodiac. In a Mithraic context he can appear as Caelus Aeternus. A form of Ahura-Mazda is invoked in Latin as Caelus Aeternus Iupiter.
The walls of some mithrea feature allegorical depictions of the cosmos with Caelus. The mithraeum of Dieburg represents the tripartite world with Caelus and Tellus below Phaeton-Heliodromus; some Roman writers used Caelum as a way to express the monotheistic god of Judaism. Juvenal identifies the Jewish god with Caelus as the highest heaven, saying that Jews worship the numen of Caelus. Florus has a passage describing the Holy of Holies in the Temple of Jerusalem as housing a "sky" under a golden vine. A golden vine the one mentioned, was sent by the Hasmonean king Aristobulus to Pompeius Magnus after his defeat of Jerusalem, was displayed in the Temple of Jupiter
Beetles are a group of insects that form the order Coleoptera, in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, distinguishing them from most other insects; the Coleoptera, with about 400,000 species, is the largest of all orders, constituting 40% of described insects and 25% of all known animal life-forms. The largest of all families, the Curculionidae with some 70,000 member species, belongs to this order. Found in every habitat except the sea and the polar regions, they interact with their ecosystems in several ways: beetles feed on plants and fungi, break down animal and plant debris, eat other invertebrates; some species are serious agricultural pests, such as the Colorado potato beetle, while others such as Coccinellidae eat aphids, scale insects and other plant-sucking insects that damage crops. Beetles have a hard exoskeleton including the elytra, though some such as the rove beetles have short elytra while blister beetles have softer elytra; the general anatomy of a beetle is quite uniform and typical of insects, although there are several examples of novelty, such as adaptations in water beetles which trap air bubbles under the elytra for use while diving.
Beetles are endopterygotes, which means that they undergo complete metamorphosis, with a series of conspicuous and abrupt changes in body structure between hatching and becoming adult after a immobile pupal stage. Some, such as stag beetles, have a marked sexual dimorphism, the males possessing enormously enlarged mandibles which they use to fight other males. Many beetles are aposematic, with bright colours and patterns warning of their toxicity, while others are harmless Batesian mimics of such insects. Many beetles, including those that live in sandy places, have effective camouflage. Beetles are prominent in human culture, from the sacred scarabs of ancient Egypt to beetlewing art and use as pets or fighting insects for entertainment and gambling. Many beetle groups are brightly and attractively coloured making them objects of collection and decorative displays. Over 300 species are used as food as larvae. However, the major impact of beetles on human life is as agricultural and horticultural pests.
Serious pests include the boll weevil of cotton, the Colorado potato beetle, the coconut hispine beetle, the mountain pine beetle. Most beetles, however, do not cause economic damage and many, such as the lady beetles and dung beetles are beneficial by helping to control insect pests; the name of the taxonomic order, comes from the Greek koleopteros, given to the group by Aristotle for their elytra, hardened shield-like forewings, from koleos and pteron, wing. The English name beetle comes from the Old English word bitela, little biter, related to bītan, leading to Middle English betylle. Another Old English name for beetle is ċeafor, used in names such as cockchafer, from the Proto-Germanic *kebrô. Beetles are by far the largest order of insects: the 400,000 species make up about 40% of all insect species so far described, about 25% of all animals. A 2015 study provided four independent estimates of the total number of beetle species, giving a mean estimate of some 1.5 million with a "surprisingly narrow range" spanning all four estimates from a minimum of 0.9 to a maximum of 2.1 million beetle species.
The four estimates made use of host-specificity relationships, ratios with other taxa, plant:beetle ratios, extrapolations based on body size by year of description. Beetles are found in nearly all habitats, including freshwater and coastal habitats, wherever vegetative foliage is found, from trees and their bark to flowers and underground near roots - inside plants in galls, in every plant tissue, including dead or decaying ones; the heaviest beetle, indeed the heaviest insect stage, is the larva of the goliath beetle, Goliathus goliatus, which can attain a mass of at least 115 g and a length of 11.5 cm. Adult male goliath beetles are the heaviest beetle in its adult stage, weighing 70–100 g and measuring up to 11 cm. Adult elephant beetles, Megasoma elephas and Megasoma actaeon reach 50 g and 10 cm; the longest beetle is the Hercules beetle Dynastes hercules, with a maximum overall length of at least 16.7 cm including the long pronotal horn. The smallest recorded beetle and the smallest free-living insect, is the featherwing beetle Scydosella musawasensis which may measure as little as 325 µm in length.
The oldest known fossil insect that unequivocally resembles a Coleopteran is from the Lower Permian Period about 270 million years ago, though these members of the family Tshekardocoleidae have 13-segmented antennae, elytra with more developed venation and more irregular longitudinal ribbing, abdomen and ovipositor extending beyond the apex of the elytra. In the Permian–Triassic extinction event at the end of the Permian, some 30% of all insect species became extinct, so the fossil record of insects only includes beetles from the Lower Triassic 220 mya. Around this time, during the Late Triassic, fungus-feeding species such as Cupedidae appear in the fossil record. In the stages of the Upper Triassic, alga-feeding insects such as Triaplidae and Hydrophilidae begin to appear, alongside predatory water beetles; the first weevils, including the Obrienidae, appear alongside the first rove beetles, which resemb
Insects or Insecta are hexapod invertebrates and the largest group within the arthropod phylum. Definitions and circumscriptions vary; as used here, the term Insecta is synonymous with Ectognatha. Insects have a chitinous exoskeleton, a three-part body, three pairs of jointed legs, compound eyes and one pair of antennae. Insects are the most diverse group of animals; the total number of extant species is estimated at between ten million. Insects may be found in nearly all environments, although only a small number of species reside in the oceans, which are dominated by another arthropod group, crustaceans. Nearly all insects hatch from eggs. Insect growth is constrained by the inelastic exoskeleton and development involves a series of molts; the immature stages differ from the adults in structure and habitat, can include a passive pupal stage in those groups that undergo four-stage metamorphosis. Insects that undergo three-stage metamorphosis lack a pupal stage and adults develop through a series of nymphal stages.
The higher level relationship of the insects is unclear. Fossilized insects of enormous size have been found from the Paleozoic Era, including giant dragonflies with wingspans of 55 to 70 cm; the most diverse insect groups appear to have coevolved with flowering plants. Adult insects move about by walking, flying, or sometimes swimming; as it allows for rapid yet stable movement, many insects adopt a tripedal gait in which they walk with their legs touching the ground in alternating triangles, composed of the front & rear on one side with the middle on the other side. Insects are the only invertebrates to have evolved flight, all flying insects derive from one common ancestor. Many insects spend at least part of their lives under water, with larval adaptations that include gills, some adult insects are aquatic and have adaptations for swimming; some species, such as water striders, are capable of walking on the surface of water. Insects are solitary, but some, such as certain bees and termites, are social and live in large, well-organized colonies.
Some insects, such as earwigs, show maternal care, guarding their eggs and young. Insects can communicate with each other in a variety of ways. Male moths can sense the pheromones of female moths over great distances. Other species communicate with sounds: crickets stridulate, or rub their wings together, to attract a mate and repel other males. Lampyrid beetles communicate with light. Humans regard certain insects as pests, attempt to control them using insecticides, a host of other techniques; some insects damage crops by feeding on sap, fruits, or wood. Some species are parasitic, may vector diseases; some insects perform complex ecological roles. Insect pollinators are essential to the life cycle of many flowering plant species on which most organisms, including humans, are at least dependent. Many insects are considered ecologically beneficial as predators and a few provide direct economic benefit. Silkworms produce silk and honey bees produce honey and both have been domesticated by humans.
Insects are consumed as food in 80% of the world's nations, by people in 3000 ethnic groups. Human activities have effects on insect biodiversity; the word "insect" comes from the Latin word insectum, meaning "with a notched or divided body", or "cut into", from the neuter singular perfect passive participle of insectare, "to cut into, to cut up", from in- "into" and secare "to cut". A calque of Greek ἔντομον, "cut into sections", Pliny the Elder introduced the Latin designation as a loan-translation of the Greek word ἔντομος or "insect", Aristotle's term for this class of life in reference to their "notched" bodies. "Insect" first appears documented in English in 1601 in Holland's translation of Pliny. Translations of Aristotle's term form the usual word for "insect" in Welsh, Serbo-Croatian, etc; the precise definition of the taxon Insecta and the equivalent English name "insect" varies. In the broadest circumscription, Insecta sensu lato consists of all hexapods. Traditionally, insects defined in this way were divided into "Apterygota" —the wingless insects—and Pterygota—the winged insects.
However, modern phylogenetic studies have shown that "Apterygota" is not monophyletic, so does not form a good taxon. A narrower circumscription restricts insects to those hexapods with external mouthparts, comprises only the last three groups in the table. In this sense, Insecta sensu stricto is equivalent to Ectognatha. In the narrowest circumscription, insects are restricted to hexapods that are either winged or descended from winged ancestors. Insecta sensu strictissimo is equivalent to Pterygota. For the purposes of this article, the middle definition is used; the evolutionary relationship of insects to other animal groups remains unclear. Although traditionally grouped with millipedes and centiped
Polyphaga is the largest and most diverse suborder of beetles. It comprises 144 families in 16 superfamilies, displays an enormous variety of specialization and adaptation, with over 300,000 described species, or 90% of the beetle species so far discovered. Key characteristics of Polyphaga are that the hind coxa, does not divide the first and second abdominal/ventral plates which are known as sternites; the notopleural suture is not present. The name of polyphaga is derived from two Greek words: poly-, meaning'many', phagein, meaning'to eat', so the suborder is called the “eaters of many things”; the five infraorders are: Bostrichiformia — including furniture beetles and skin beetles Cucujiformia — includes lady beetles, longhorn beetles, checkered beetles and leaf beetles Elateriformia — includes click beetles and fireflies Scarabaeiformia — includes scarab beetles, stag beetles, dung beetles Staphyliniformia — includes rove beetles and water scavenger beetlesThe internal classification of Polyphaga involves several superfamilies or series, whose constituents are stable, although some smaller families are allocated to different clades by different authors.
Large superfamilies include Hydrophiloidea, Scarabaeoidea, Byrrhoidea and Bostrichoidea. The infraorder Cucujiformia includes the vast majority of phytophagous beetles, united by cryptonephric Malpighian tubules of the normal type, a cone ommatidium with open rhabdom, lack of functional spiracles on the eighth abdominal segment. Constituent superfamilies of Cucujiformia are Cleroidea, Tenebrionoidea and Curculionoidea. Evidently adoption of a phytophagous lifestyle correlates with taxon diversity in beetles, with Cucujiformia weevils, forming a major radiation. List of subgroups of the order Coleoptera Peter S. Cranston and Penny J. Gullan, University of California,Phylogeny of Insects, page 893. Phylogeny of Insects Site devoted to Staphyliniformia Project devoted to studying rove beetles Image of a click beetle site devoted to stag beetles news article highlighting the damage caused by Longhorn beetles "Polyphaga". Atlas of Living Australia
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