Animal Classification

Animal Classification

With over 2 million species classified into 30 phyla, Kingdom Animalia surpasses the other 4 kingdoms in terms of its species diversity.

Animals are “multicellular” (composed of many cells). In most animals, these cells are organized into tissues that make up different organs and organ systems. The exception is the sponges.

All animals are heterotrophs, meaning that they must obtain energy and nourishment by consuming other organisms. All animals require oxygen for their metabolism, can sense and respond to their environment, and have the capacity to reproduce sexually (though many reproduce asexually, as well).

The classification system consists of seven main levels, although some have sub groupings, as well:

Kingdom: A kingdom is the broadest level. It contains the most kinds of organisms. The relationships among organisms in a kingdom are extremely loose.

Phylum: Phylum is the major taxonomic group of animals and plants. Within the kingdoms, organisms are divided by general characteristics. For example, in the Animal Kingdom, animals with backbones are placed in a separate phylum from animals without backbones.

Class: Organisms in a phylum are divided into classes that further group similarities. In the Animal Kingdom, for example, birds, mammals, and fish all group in their own classes. Among plants, the angiosperm class comprises all flowering plants, and all conifers, such as pines and spruces, make up the conifer class.

Order: Scientific groupings don’t follow hard and fast rules. After you get to the “order” of a living thing, there’s disagreement about where it belongs. You may find that different scientific organizations group creatures in different orders or families.

Family: Families further divide organisms of the same class by similar characteristics. Not all scientific organizations may agree to the exact family an organization should be classified in.

Genus: Two or more species that share unique body structures or other characteristics are considered to be closely related and are placed together in a genus. Sometimes a genus may include only a single species if there’s nothing else in the world that has similarities with it.

Species: A species is the most specific level. It contains the fewest organisms. The relationship between organisms in a species is very close.

Kingdom: Animalia (Metazoa or metazoans)   Phylum: Annelida (Segmented Worms – earthworms, leeches)

The annelids include earthworms, polychaete worms, and leeches. All members of the group are to some extent made up of segments that are formed by subdivisions that partially transect the body cavity. Segments each contain elements of such body systems as circulatory, nervous, and excretory tracts. The internal organs of annelids are well developed. They include a closed, segmentally-arranged circulatory system. The digestive system is a complete tube with mouth and anus. Gases are exchanged through the skin, or sometimes through specialized gills. Annelida can be either sexual or asexual animals. Members of the Phylum Annelida can be found throughout the world, in marine, freshwater, and terrestrial environments. Ecologically, they range from passive filter feeders to voracious and active predators.

Phylum:  Arthropoda  (Arthropods:Spiders,Insects,Crabs)                                1,140,000 species

The Phylum Arthropoda is the largest phylum of animals and include the insects, arachnids, crustaceans, and others. Arthropods are characterized by the possession of a segmented body with appendages on at least one segment. They have a dorsal heart and a ventral nervous system. All arthropods are covered by a hard exoskeleton.

Phylum: Brachiopoda (Lamp Shells)                              About 350 species

The Brachiopoda, or Lampshells are an ancient phylum of filter feeding marine worms. Upon first glance, they look like clams, but they are actually quite different in their anatomy, and they are not closely related to the molluscs. The bodies of brachiopods are enclosed in a double shell. They are small animals with the largest living species having a shell length of about 10 cm (4 in) and most species are much smaller. Brachiopods often make their homes in very cold water, either in polar regions or at great depths in the ocean.

Phylum: Bryozoa (Moss Animals)                  About 5,000 species

Bryozoans are tiny colonial animals that generally build stony skeletons of calcium carbonate, superficially similar to coral. They are also known as moss animals (which is the literal Greek translation) or sea mats. They generally prefer warm, tropical waters but are known to occur worldwide. Most species of Bryozoan live in marine environments, though there are about 50 species which inhabit freshwater.

Phylum: Chordata (Animals with a notocord)                   51,000 species

Chordata contains the most familiar species, including humans. All chordates have several things in common that occur at some stage of development. They have pharyngeal slits, which are openings that connect the inside of the throat to the outside of the neck. These are often used as gills. Their main feature, what they are named after, is the notochord, which is a rod that supports the nerve cord. The nerve cord is also present in all species. This is a bundle of nerve fibers which connect the brain with the muscles and organs, and is through which messages from the brain are sent. A tail is also present, which extends past the anal opening. In most species, at least some of these features disappear with age. For example, the pharyngeal slits are only present in the human fetus.

SubPhylum: Cephalochordata (lancelets OR amphioxus)                          25 species

This is a small, very unusual subphylum of creatures. These animals are fish-like in appearance, but are invertebrates with a notochord, and a nerve cord right above it. They lack bones, a brain, eyes, and most other organs associated with the brain. There are 25 species, and they do not seem to be placed in any class. However, some experts do not call this a subphylum and they place it in a class of the same name.

SubPhylum: Urochordata (Tunicata: sea squirts, salps)                                   3,000 species

This is a large subphylum of unusual invertebrates that do not look like anything much more than a strange underwater worm or mushroom. They start off life as tadpole-like larvae with notochords and all the rest. This stage lasts only a short time, after which they anchor to the seabed and live a sedentary life. They completely change shape at this point, and it is hard to believe that they are in the same phylum as humans. The adults lack the notochord but do keep the pharyngeal slits. They have a highly-developed internal structure, with a heart and other organs. Tunicates are named for their protective covering, known as a tunic. This tunic is made up of cellulose, which is very rare in animals. Class: Appendicularia or Larvacea (free swimming tunicates)Class: Ascidiaceae (sea squirts)Class: Sorberacea (benthic tunicates)Class: Thaliacea (salps)

SubPhylum: Vertebrata                             (vertebrates – Animals with backbones)                              41,700 species

This is the largest subphylum and the focus of this website. It contains the more well-known land animals, including humans, reptiles, fish, marine mammals, and birds. Every animal with a backbone is present in this subphylum. The notochord is developed at an early age, and is replaced with vertebrate. All vertebrates have a skeleton of either bone or cartilage. Their brain is protected by a boney cranium, and consists of three parts. They all have well-developed hearts with 2-4 chambers and have a closed circulatory system.

Class: Amphibia (Amphibians – frogs, salamanders)(4,000 species)

Class: Aves (Birds – 9,090 species)

Class: Cephalaspidomorphi (Lampreys – 73 species)

Class: Chondrichthyes (Pices – cartilaginous fish)

Class: Mammalia (mammals – 4,620 species)

The mammals are the class of vertebrate animals primarily characterized by the presence of mammary glands, which in females produce milk for the nourishment of young; the presence of hair or fur; and which have endothermic or “warm blooded” bodies. The brain regulates endothermic and circulatory systems, including a four-chambered heart. Mammals encompass more than 5,000 genera, distributed in 425 families and up to 46 orders (the number depends on the classification scheme adopted).

Class: Myxini (Hagfish)

Although hagfish are sometimes called “slime eels,” they are not eels at all. Myxini is the only class in the clade Craniata that does not also belong to the subphylum Vertebrata. The hagfish is a more primitive fish than the bony or cartilaginous fish. The hagfish is known as the sea’s most disgusting creature, due to it’s ability to produce buckets of slime in a couple minutes as an escape mechanism.

Class: Osteichthyes (Pices – bony fish – 29,000 species with many more unidentified)

The Osteichthyes class is the largest in the Vertebrata sub-phylum. The Osteichthyes are a taxonomic superclass of fish, also called bony fish that includes the ray-finned fish and lobe finned fish. The vast majority of fish are osteichthyes.

Class: Reptilia (reptiles: Crocodiles, Aligators, Snakes,Turtles)            6,000 species

Reptiles are air-breathing, cold-blooded vertebrates that have skin covered in scales as opposed to hair or feathers. They are tetrapods (having or having descended from vertebrates with four limbs) and amniotes, whose embryos are surrounded by an amniotic membrane. Modern reptiles inhabit every continent with the exception of Antarctica, and are represented by four living orders.

Phylum: Cnidaria (Corals, Jellyfishes, Sea Anemones)    Phylum: Ctenophora (Comb Jellies)    Phylum: Echinodermata (Sea Urchins & Starfish)    Phylum: Mollusca (Molluscs:Snails, Clams, Squid & Octopus)                            about 80,000 species

Mollusks have three distinct divisions of their body. The head contains the sensory equipment (eyes, antennae, etc) and the primitive brain. The visceral hump, which is the main body, contains most of the organs, including a complete digestive and excretory tract as well as the reproductive organs. The visceral hump also includes the two external flaps of tissue, which are known as the mantle. The mantle excretes the material that forms the shell on some species, and it protects the mantle cavity. The mantle cavity contains the gills, which excrete waste and circulate oxygen. Most mollusks have a shell, which sits on the visceral hump and acts as a “home”, much like a turtle shell. It protects the main body from predators. The third body section is the foot, which enables locomotion. Even clams have a foot. Most mollusks have a special tongue-like organ known as the radula. The radula is composed of chitin, much like the exoskeleton of an arthropod, and is covered in pointy “teeth”. The radula can be used to scrape food off rocks and to kill larger prey.

Class: Caudofoveata (70 species) Class: Solengogastres (250 species)Class: Gastropoda snails and slugs (about 70,000 species)Class: Polyplacophora chitons (about 600 species )Class: Cephalopoda (squids, cuttlefish, octopuses, nautiloids –   about 800)Class: Monoplacophora (monoplacophorans – 12 species)Order: Bivalvia bivalves (about 8,000 species)Order: Scaphopoda tusk shells (350 species)   Phylum: Nematoda (Roundworms)   Phylum: Nemertea (Proboscis Worms)   Phylum: Phoronida (horseshoe worms)   Phylum: Platyhelminthes (Flatworms)   Phylum: Porifera (Sponges)   |–Archaeocyatha     `–+–Stromatoporoidea   |–+–Hexactinellida     |  `–Demospongiae     |   |–Ceractinomorpha     |   `–Tetractinomorpha   `–+–Calcarea      `–+–CNIDARIA      `–BILATERIA   Phylum: Onychophora (Velvet Worms)   Phylum: Rotifera (Microscopic Aquatic Animals)


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A brief explanation of how Animal Classification works( for the average guy)

Scientists never agree on much of anything, so there are several accepted Plant and Animal Classification systems. Most of us don’t even know what the names of those classification systems mean, let alone understand the structure of them, so we are just going to use a simplified dummied up system the average common man can understand.