A report on Animal

Animals are unique in having the ball of cells of the early embryo (1) develop into a hollow ball or blastula (2).
Sexual reproduction is nearly universal in animals, such as these dragonflies.
Predators, such as this ultramarine flycatcher (Ficedula superciliaris), feed on other animals.
Hydrothermal vent mussels and shrimps
The blue whale is the largest animal that has ever lived.
Dickinsonia costata from the Ediacaran biota (c. 635–542 MYA) is one of the earliest animal species known.
Anomalocaris canadensis is one of the many animal species that emerged in the Cambrian explosion, starting some 539 million years ago, and found in the fossil beds of the Burgess shale.
Non-bilaterians include sponges (centre) and corals (background).
Idealised bilaterian body plan. With an elongated body and a direction of movement the animal has head and tail ends. Sense organs and mouth form the basis of the head. Opposed circular and longitudinal muscles enable peristaltic motion.
The bilaterian gut develops in two ways. In many protostomes, the blastopore develops into the mouth, while in deuterostomes it becomes the anus.
Ecdysis: a dragonfly has emerged from its dry exuviae and is expanding its wings. Like other arthropods, its body is divided into segments.
Spiral cleavage in a sea snail embryo
Jean-Baptiste de Lamarck led the creation of a modern classification of invertebrates, breaking up Linnaeus's "Vermes" into 9 phyla by 1809.
Sides of beef in a slaughterhouse
A gun dog retrieving a duck during a hunt
Artistic vision: Still Life with Lobster and Oysters by Alexander Coosemans, c. 1660
Auroralumina attenboroughii, an Ediacaran predator (c. 560 mya)

Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia.

- Animal
Animals are unique in having the ball of cells of the early embryo (1) develop into a hollow ball or blastula (2).

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Cnidaria

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Pacific sea nettles, Chrysaora fuscescens
Oral end of actinodiscus polyp
Firing sequence of the cnida in a hydra's nematocyst Operculum (lid) "Finger" that turns inside out / / / Barbs  Venom  Victim's skin  Victim's tissues
A hydra's nematocyst, before firing. "trigger" cilium
Stranded scyphozoans on a Cambrian tidal flat in Blackberry Hill, Wisconsin.
The fossil coral Cladocora from Pliocene rocks in Cyprus
Illustrated tree of cnidarians and their closest relatives
The dangerous Carukia barnesi, one of the known species of box jellyfish which can cause Irukandji syndrome.
Cerianthus filiformis (Ceriantharia)
Sea anemones (Actinaria, part of Hexacorallia)
Coral Acropora muricata (Scleractinia, part of Hexacorallia)
Sea fan Gorgonia ventalina (Alcyonacea, part of Octocorallia)
Box jellyfishCarybdea branchi (Cubozoa)
Siphonophore Physalia physalis (Hydrozoa)
Myxobolus cerebralis (Myxozoa)
Polypodium hydriforme (Polypodiozoa)
Jellyfish Phyllorhiza punctata (Scyphozoa)
Stalked jelly Haliclystus antarcticus (Staurozoa)

Cnidaria is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter.

Sponge

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Sponges, the members of the phylum Porifera (meaning 'pore bearer'), are a basal animal clade as a sister of the Diploblasts.

Sponges, the members of the phylum Porifera (meaning 'pore bearer'), are a basal animal clade as a sister of the Diploblasts.

Sponge biodiversity and morphotypes at the lip of a wall site in 60 ft of water. Included are the yellow tube sponge, Aplysina fistularis, the purple vase sponge, Niphates digitalis, the red encrusting sponge, Spirastrella coccinea, and the gray rope sponge, Callyspongia sp.
Cells of the protist choanoflagellate clade closely resemble sponge choanocyte cells. Beating of choanocyte flagella draws water through the sponge so that nutrients can be extracted and waste removed.
Spongia officinalis, "the kitchen sponge", is dark grey when alive.
Euplectella aspergillum, a glass sponge known as "Venus' flower basket"
The carnivorous ping-pong tree sponge, Chondrocladia lampadiglobus
The freshwater sponge Spongilla lacustris
Euplectella aspergillum is a deep ocean glass sponge; seen here at a depth of 2572 m off the coast of California
Holes made by clionaid sponge (producing the trace Entobia) after the death of a modern bivalve shell of species Mercenaria mercenaria, from North Carolina
Close-up of the sponge boring Entobia in a modern oyster valve. Note the chambers which are connected by short tunnels.
Demosponge Samus anonymus (up to 50 m), hexactinellid Scleroplegma lanterna (~100–600 m), hexactinellid Aulocalyx irregularis (~550–915 m), lithistid demosponge Neoaulaxinia persicum (~500–1,700 m)
Steps of the sponge loop pathway: (1) corals and algae release exudates as dissolved organic matter (DOM), (2) sponges take up DOM, (3) sponges release detrital particulate organic matter (POM), (4) sponge detritus (POM) is taken up by sponge-associated and free-living detritivores.
The sponge holobiont is an example of the concept of nested ecosystems. Key functions carried out by the microbiome (colored arrows) influence holobiont functioning and, through cascading effects, subsequently influence community structure and ecosystem functioning. Environmental factors act at multiple scales to alter microbiome, holobiont, community, and ecosystem scale processes. Thus, factors that alter microbiome functioning can lead to changes at the holobiont, community, or even ecosystem level and vice versa, illustrating the necessity of considering multiple scales when evaluating functioning in nested ecosystems.
Raphidonema faringdonense, a fossil sponge from the Cretaceous of England
Oxygen content of the atmosphere over the last billion years. If confirmed, the discovery of fossilized sponges dating to 890 million years ago would predate the Neoproterozoic Oxygenation Event (800-500 million years BP).
A choanoflagellate
A comb jelly
Sponges made of sponge gourd for sale alongside sponges of animal origin (Spice Bazaar at Istanbul, Turkey).
Natural sponges in Tarpon Springs, Florida
Display of natural sponges for sale on Kalymnos in Greece
Halichondria produces the eribulin precursor halichondrin B

Sponges constitute the phylum Porifera, and have been defined as sessile metazoans (multicelled immobile animals) that have water intake and outlet openings connected by chambers lined with choanocytes, cells with whip-like flagella.

Bilateria

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Idealised wormlike nephrozoan body plan. With a cylindrical body and a direction of movement the animal has head and tail ends. Sense organs and mouth form the basis of the head. Opposed circular and longitudinal muscles enable peristaltic motion.
Ikaria wariootia, living 571-539 million years ago is one of the oldest bilaterians identified

The Bilateria or bilaterians are animals with bilateral symmetry as an embryo, i.e. having a left and a right side that are mirror images of each other.

Clockwise from top left: Blepharisma japonicum, a ciliate; Giardia muris, a parasitic flagellate; Centropyxis aculeata, a testate (shelled) amoeba; Peridinium willei, a dinoflagellate; Chaos carolinense, a naked amoebozoan; Desmarella moniliformis, a choanoflagellate

Protozoa

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Informal term for a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris.

Informal term for a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris.

Clockwise from top left: Blepharisma japonicum, a ciliate; Giardia muris, a parasitic flagellate; Centropyxis aculeata, a testate (shelled) amoeba; Peridinium willei, a dinoflagellate; Chaos carolinense, a naked amoebozoan; Desmarella moniliformis, a choanoflagellate
Class Protozoa, order Infusoria, family Monades by Georg August Goldfuss, c. 1844
John Hogg's illustration of the Four Kingdoms of Nature, showing "Primigenal" as a greenish haze at the base of the Animals and Plants, 1860
The ciliate Spirostomum ambiguum can attain 3 mm in length
Isotricha intestinalis, a ciliate present in the rumen of sheep.
Paramecium bursaria, is one example of a variety of freshwater ciliates that host endosymbiont chlorophyte algae from the genus Chlorella
Resting cyst of ciliated protozoan Dileptus viridis.
Life cycle of parasitic protozoan, Toxoplasma gondii
Trophozoites of the amoebic dysentery pathogen Entamoeba histolytica with ingested human red blood cells (dark circles)

Historically, protozoans were regarded as "one-celled animals", because they often possess animal-like behaviours, such as motility and predation, and lack a cell wall, as found in plants and many algae.

Eukaryote

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Eukaryotes are organisms whose cells have a nucleus enclosed within a nuclear envelope.

Eukaryotes are organisms whose cells have a nucleus enclosed within a nuclear envelope.

The endomembrane system and its components
Simplified structure of a mitochondrion
Longitudinal section through the flagellum of Chlamydomonas reinhardtii
Structure of a typical animal cell
Structure of a typical plant cell
Fungal Hyphae cells: 1 – hyphal wall, 2 – septum, 3 – mitochondrion, 4 – vacuole, 5 – ergosterol crystal, 6 – ribosome, 7 – nucleus, 8 – endoplasmic reticulum, 9 – lipid body, 10 – plasma membrane, 11 – spitzenkörper, 12 – Golgi apparatus
This diagram illustrates the twofold cost of sex. If each individual were to contribute the same number of offspring (two), (a) the sexual population remains the same size each generation, where the (b) asexual population doubles in size each generation.
Phylogenetic and symbiogenetic tree of living organisms, showing a view of the origins of eukaryotes and prokaryotes
One hypothesis of eukaryotic relationships – the Opisthokonta group includes both animals (Metazoa) and fungi, plants (Plantae) are placed in Archaeplastida.
A pie chart of described eukaryote species (except for Excavata), together with a tree showing possible relationships between the groups
The three-domains tree and the Eocyte hypothesis
Phylogenetic tree showing a possible relationship between the eukaryotes and other forms of life; eukaryotes are colored red, archaea green and bacteria blue
Eocyte tree.
Diagram of the origin of life with the Eukaryotes appearing early, not derived from Prokaryotes, as proposed by Richard Egel in 2012. This view implies that the UCA was relatively large and complex.

Animals, plants, and fungi are the most familiar eukaryotes; other eukaryotes are sometimes called protists.

A Caenorhabditis elegans stained to highlight the nuclei of its cells

Multicellular organism

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Organism that consists of more than one cell, in contrast to a unicellular organism.

Organism that consists of more than one cell, in contrast to a unicellular organism.

A Caenorhabditis elegans stained to highlight the nuclei of its cells
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All species of animals, land plants and most fungi are multicellular, as are many algae, whereas a few organisms are partially uni- and partially multicellular, like slime molds and social amoebae such as the genus Dictyostelium.

Arthropod

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Arthropods (, (gen.

Arthropods (, (gen.

Structure of a biramous appendage.
Alignment of anterior body segments and appendages across various arthropod taxa, based on the observations until mid 2010s. Head regions in black.
Illustration of an idealized arthropod exoskeleton.
Cicada climbing out of its exoskeleton while attached to tree
Arthropod eyes
Head of a wasp with three ocelli (center), and compound eyes at the left and right
Compsobuthus werneri female with young (white)
The nauplius larva of a penaeid shrimp
Marrella, one of the puzzling arthropods from the Burgess Shale
Kylinxia
The velvet worm (Onychophora) is closely related to arthropods
Insects and scorpions on sale in a food stall in Bangkok, Thailand

ποδός)) are invertebrate animals having an exoskeleton, a segmented body, and paired jointed appendages.

Opabinia made the largest single contribution to modern interest in the Cambrian explosion.

Cambrian explosion

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Opabinia made the largest single contribution to modern interest in the Cambrian explosion.
This Marrella specimen illustrates how clear and detailed the fossils from the Burgess Shale Lagerstätte are.
Rusophycus and other trace fossils from the Gog Group, Middle Cambrian, Lake Louise, Alberta, Canada
Stem groups
Stromatolites (Pika Formation, Middle Cambrian) near Helen Lake, Banff National Park, Canada
Modern stromatolites in Hamelin Pool Marine Nature Reserve, Western Australia
An Ediacaran trace fossil, made when an organism burrowed below a microbial mat.
Dickinsonia costata, an Ediacaran organism of unknown affinity, with a quilted appearance
Fossil of Kimberella, a triploblastic bilaterian, and possibly a mollusc
A fossilized trilobite, an ancient type of arthropod: This specimen, from the Burgess Shale, preserves "soft parts" – the antennae and legs.

The Cambrian explosion, Cambrian radiation, Cambrian diversification, or the Biological Big Bang refers to an interval of time approximately in the Cambrian Period when practically all major animal phyla started appearing in the fossil record.

Cross-section of an oligochaete worm. The worm's body cavity surrounds the central typhlosole.

Coelom

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Main body cavity in most animals and is positioned inside the body to surround and contain the digestive tract and other organs.

Main body cavity in most animals and is positioned inside the body to surround and contain the digestive tract and other organs.

Cross-section of an oligochaete worm. The worm's body cavity surrounds the central typhlosole.
Classification of tripoblasts based on body cavities

In some animals, it is lined with mesothelium.

A selection of animals showing a range of possible body symmetries, including asymmetry, radial, and bilateral body plans

Symmetry in biology

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Symmetry in biology refers to the symmetry observed in organisms, including plants, animals, fungi, and bacteria.

Symmetry in biology refers to the symmetry observed in organisms, including plants, animals, fungi, and bacteria.

A selection of animals showing a range of possible body symmetries, including asymmetry, radial, and bilateral body plans
Illustration depicting the difference between bilateral (Drosophila), radial (actinomorphic flowers) and spherical (coccus bacteria) symmetry
Lilium bulbiferum displays hexamerism with repeated parts arranged around the axis of the flower.
Apple cut horizontally showing that pentamerism also occurs in fruit
Gastroenteritis viruses have icosahedral symmetry
Volvox is a microscopic green freshwater alga with spherical symmetry. Young colonies can be seen inside the larger ones.
The small emperor moth, Saturnia pavonia, displays a deimatic pattern with bilateral symmetry.
Flower of bee orchid (Ophrys apifera) is bilaterally symmetrical (zygomorphic). The lip of the flower resembles the (bilaterally symmetric) abdomen of a female bee; pollination occurs when a male bee attempts to mate with it.
Schematic diagram of signalling pathways on the left and right side of a chick embryo, ultimately leading to the development of asymmetry
Head of a male crossbill showing asymmetrical upper and lower beak
A winter flounder, a type of flatfish, with both eyes on the same side of its head
Hermit crabs have different sized claws
A Roman snail and its helical shell
Chicoreus palmarosae, a sea snail, illustrating asymmetry, which is seen in all gastropods in the form of a helical shell
A red slug, clearly showing the pneumostome
alt=Illustration of adult caribou in profile.|Male caribou usually possess one brow tine flattened into a shovel shape<ref>{{Cite journal|last=Goss|first=Richard J.|date=1990-06-01|title=Interactions between asymmetric brow tines in caribou and reindeer antlers|url=https://www.nrcresearchpress.com/doi/abs/10.1139/z90-165|journal=Canadian Journal of Zoology|volume=68|issue=6|pages=1115–1119|doi=10.1139/z90-165|issn=0008-4301}}</ref>

The Radiata, animals with radial symmetry, formed one of the four branches of Georges Cuvier's classification of the animal kingdom.