What is an animal? Kingdom Animalia divided into two major groups:– invertebrates– vertebratesWorm Snail Cockroach An invertebrate is an animal without abackbone. About 98 percent of all animals areinvertebrates.Invertebrate
Vertebrates Only about two percent of all animals are vertebrateswhich belong to the Phylum Chordata. Vertebrates include fish, amphibians, reptiles, birds, andmammals.BirdFrog RatAnimals share the following characteristics:1. Animals are multi cellular and have eukaryotic cells.2. Animal cells lack cell walls.3. Animals have a period of embryonic development.4. Animals are consumers.5. Animals can move.6. Most animals have muscle and nervous tissue.7. Animals are diploid.
Animals have different levels of organization. Some animals consist of cells with a few tissue layers. Others are complex with organ systems. All animals have sex cells that are haploid and areproduced by meiosis. All animal life cycles consist of haploid and diploid celldevelopment.
Animal body plan and Symmetry The arrangement of an animal’s body parts is called itssymmetry. Animals that do not have an orderly body plan, likesponges, are called asymmetrical. Radial symmetry means that the body parts are arrangedin a circle around a central point. In bilateral symmetry, the body consists of two similarhalves.
The gut is the digestive tract. It enables an animal to digest foodoutside of its cells. In animals without a gut (likesponges), food is digested inside oftheir cells. Complex animals also have a bodycavity that holds the gut and otherorgans. The body cavity provides an openspace for organs to grow andfunction.
As animals evolved and became more complex, theydeveloped organ systems to perform basic functions.Organ Systems Some important organ systems are:– Skeletal– Muscular– Circulatory– Digestive– Nervous– Reproductive Sponges belong to the PhylumPorifera (“pore bearing.”) They are asymmetrical and do nothave a body cavity.Sponges
Adult sponges do not move around. They feed by pulling water into thepores of their bodies and filtering outfood particles. They have specialized collar cells thatmove water and collect and digest food.Cnidarians The Phylum Cnidarians includesjellyfish, coral, sea anemones, andhydra. They have radial symmetry and donot have a body cavity. Cnidarians have differentiated cellsthat are organized into two layers oftissues and nerves that form anetwork. Many cnidarians have specializedstinging cells to capture food ordefend themselves.
Flatworms Planarians belong to the Phylum Platy helminthes—theflatworms. Flatworms are the simplest animals having bilateral symmetry. They have a sac-like gut but no body cavity. Planarians secrete digestiveenzymes onto their food and suckthe food particles through anorgan called a pharynx. They digest food in a gastrovascular cavity.Roundworms Members of the Phylum Nematode arecalled roundworms. Roundworms are the simplest animalswith a complete gut that runs frommouth to anus.
Annelids Earthworms belong to the Phylum Annelida. All annelids have bodies that are divided into individualsegments. Annelids have bilateral symmetry and a true body cavity.
Mollusks Snails, clams, and squids are allmembers of the Phylum Mollusca. Mollusks have bilateral symmetry and atrue body cavity. The body of a mollusk typically has afoot, gut, mantle, and shell.Body of a mollusk
Mollusks Clams and their relatives have a simple nervous system withnerve cords and a few ganglia. Octopi and their relatives have a more advanced nervoussystem. An octopus has a well-developed brain and eyes. Most mollusks have a sense of touch and taste.Arthropods The Phylum Arthropod includesinsects, spiders, and crustaceans suchas lobsters and crabs. Arthropods have segmentedbodies, jointed limbs, anexoskeleton, and well-developed organsystems. Like annelids, arthropod bodies are segmented. Some segments form three distinct regions: ahead, a thorax, and an abdomen.
Echinoderms The Phylum Echinodermata (meaning “spinyskin”) includes starfish, sea urchins, and seacucumbers. Echinoderms have radial symmetry, a bodycavity, an internal skeleton, and spiny skin. Echinoderms have a specialized watervascular system. The water vascular system is a network offluid-filled canals connected to hundreds oftiny, tube-like feet. The water vascular system helps them moveand capture food.
Vertebrate structure and function Humans and sea squirts are members of thePhylum Chordata (called chordates). All chordates have a structure called anotochord. A notochord is a flexible, rod-shapedstructure found in the embryos of allchordates.Characteristics of vertebrates All vertebrates have a backbone and a skull. The backbone is a segmented column ofinterlocking bones called vertebrae. All vertebrates have an internal skeleton forsupport, protection, and a place for muscles tobe attached. The bones and muscles of vertebrates worktogether to provide a structural framework formovement.
All vertebrates have a body cavity thatholds the organ systems.– The thoracic cavity holds the heart and thelungs of air-breathing vertebrates.– The abdominal cavity holds the digestiveorgans including the stomach, intestines, andliver.Vertebrate organs are made of four typesof tissues An organ is a group of tissues thatfunction together. Vertebrate organs are made of fourtypes of tissues:– nervous– epithelial– connective– muscle
Fish Fish are exothermic, aquatic vertebrates withfins, gills, and a streamlined body. They were the first vertebrates, and evolved about 500million years ago. There are three classes offish living today.– jawless fish– cartilaginous fish– bony fish
Amphibians Amphibians areectothermic, smooth-skinnedvertebrates, such as frogs andsalamanders, that usuallyhatch as an aquatic larva withgills.Birds Birds are endothermic, egg-laying vertebrates with forelimbsmodified to form wings. They have many adaptations forflight such asfeathers, wings, hollowbones, and air sacs.
Mammals are endothermic vertebrates that have mammaryglands. Mammary glands are organs that produce a nutritious fluidcalled milk.Mammals Mammals evolved from a now-extinctgroup of reptiles called therapsids. The earliest true mammals appearedover 200 million years ago.
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