• Animals are?multicellular,?eukaryotic?organisms
• They are?heterotrophs?and most have a?nervous system?that enables responses to the surrounding environment
• There are over?30 animal phyla, some of which are?vertebrates?and some of which are?invertebrates
  • Vertebrates have a backbone, or spinal column, while invertebrates do not
• Some of the major animal phyla include:
  • Porifera
  • Cnidaria
  • Platyhelminthes
  • Annelida
  • Mollusca
  • Arthropoda
  • Chordata

Porifera

• Simple?aquatic organisms?consisting of a?colony of cells
  • Commonly known as the?sponges
  • Once thought to be plants
• Two?layers of cells surround an internal cavity
  • They?do not have a mouth?for taking in food,?or an anus?for egestion
• Water is drawn in through?pores?in the outer layer of cells, before?suspended particles from the water?are filtered out and taken up by surrounding cells?for food
  • Porifera are?filter feeders
• There is?no symmetry?in the body plan of the porifera
• The?structure?of poriferans is supported by calcium or silica formations known as?spicules

Porifera take in water through pores for filter feeding

Cnidaria

• Aquatic organisms?also known as the coelenterates
• Their body cavity is surrounded by?two layers of cells?and has a?single opening for both ingestion and egestion
• There are?two distinct body forms?present in the cnidaria phylum
  • Polyps, or hydroids are?sessile?e.g. coral and anemones
  • Medusae?(singular?medusa)?float in the water e.g. jellyfish
  • Some cnidaria go through?both the polyp and medusa?body form during their?life cycle
• Polyps are?filter feeders, while medusae?catch prey?using?stinging cells?on their tentacles
• There is?radial?symmetry?in the body plan of the cnidaria
• Most cnidaria have?soft bodies?that rely on the surrounding water for support, but?corals secrete an exoskeleton?made of calcium carbonate

Cnidaria have two distinct body forms; polyps and medusae

Platyhelminthes

• Flat-bodied, unsegmented?worms that include the?flatworms, tapeworms,?and?flukes
• Three layers of cells?surround a branched gut with?one opening for both ingestion and egestion
• Platyhelminthes can be?free-living predators?or?scavengers, or?parasites?that feed on their hosts
• The flat body shape of platyhelminthes means that the?diffusion distance?to all cells is?short, and?no circulatory system?is present
• There is?bilateral?symmetry?in the body plan of the?platyhelminthes
• Platyhelminthes have?soft bodies?with?no skeletal support

The body structure of a member of the phylum Platyhelminthes

Annelida

• Round-bodied, segmented?worms that include the?earthworms?and the?leeches
• Each?ring-shaped body segment?contains a repetition of the structures of blood vessels and nerves
• The?gut?has separate openings for the?mouth?and?anus
• Annelida can be?free-living predators?or?scavengers, or?parasites?that feed on their hosts
• Annelida have a?closed circulatory system
• There is?bilateral?symmetry?in the body plan of the?annelida
• Annelida have?soft bodies?which are supported by a?hydroskeleton
  • The hydroskeleton is an internal fluid-filled cavity called the coelom, against which the muscles of the body wall exert pressure

The annelida have a segmented body structure

Mollusca

• A diverse group of animals that includes the?snails, slugs,?mussels,?limpets, and?octopuses
  • It is the second-largest phylum (i.e. it contains a higher number of recorded species than any other phylum, except for Arthropoda)
• Most molluscs are?aquatic, with?some terrestrial species
• The body structure contains a?muscular foot?and a?visceral?mass
  • The foot is used for?motion?and/or?anchorage?e.g. as in limpets
  • The visceral mass is located above the foot and?contains the internal organs?(i.e. it is the soft, metabolic region that contains the digestive, excretory and reproductive organs)
• The?gut?has separate openings for the?mouth?and?anus
• Mollusca have several feeding methods, including:
  • Filter feeding?e.g. in bivalves such as mussels
  • Scraping at food sources such as leaves or algae on rocks using a rough, tongue-like organ called a?radula?e.g. snails and limpets
  • Active?predation?e.g. sea slugs
• Most mollusca have an?open?circulatory system?in which the transport fluid bathes the internal organs
  • The cephalopods, which include squid and octopuses have a closed circulatory system
• There is?bilateral?symmetry?in the body plan of the?mollusca
• Mollusca have?soft bodies?that sometimes secrete a?calcium carbonate shell?from a mantle e.g. snails

The body structure of snails; members of phylum Mollusca

Arthropoda

• Animals with?segmented bodies, a?hard exoskeleton, and?jointed limbs
  • It is the?largest phylum?(i.e. it contains a higher number of recorded species than any other phylum)
  • It includes?insects, arachnids, crustaceans, centipedes, and?millipedes
• There is usually?one pair of jointed limbs per body segment, though this is not always the case
• The?gut?has separate openings for the?mouth?and?anus
• Arthropoda have an?open?circulatory system
• There is?bilateral?symmetry?in the body plan of the?arthropoda
• Arthropoda have a?hard exoskeleton?made of?chitin
  • The exoskeleton is shed as the animal grows

Insects are members of the phylum Arthropoda; they have three body segments, each with a pair of jointed limbs

Chordata

• The phylum?chordata?includes?all of the vertebrates, as well as?some invertebrates?such as the tunicates; commonly known as sea squirts
• To be classified as a chordate, an organism must have the following features?at?some stage during its development:
  • A rod-like structure along the?dorsal?length of the body known as a?notochord
    • Dorsal refers to the?back?of an organism
  • A?hollow nerve cord?located in the?dorsal?region
  • A series of slits behind the mouth known as?pharyngeal slits
  • A?tail?that extends?beyond the anus, known as a?post-anal tail
• Some chordates only have these features during the?embryonic stages?of development, e.g.
  • In vertebrates, the notochord is replaced with the spinal column in fully developed individuals
  • The dorsal hollow nerve cord develops into the brain and spinal cord in most species of chordate
  • The pharyngeal slits are only retained into adulthood in some types of chordate e.g. in the gills of fish
  • The post-anal tail has become a vestigial structure in the great apes
    • Vestigial structures are those that have lost their function, and are sometimes known as 'evolutionary leftovers'

Human embryos have all of the features of phylum chordata

Phyla Features Table

• The vertebrates are organisms that have a?spinal column?made up of?vertebrae
• There are 5?major classes?of vertebrate
  • Bony ray-finned fish (27 000 species)
    • There are other classes of fish, e.g. the bony lobe-finned fish (6 species), and the cartilaginous fish, whose skeletons are made of cartilage rather than bone (around 900 species)

     

  • Amphibians (6000 species)
  • Reptiles (9000 species)
  • Birds (10 000 species)
  • Mammals (5 700 species)
• The 5 classes can be recognised by their features

Bony ray-finned fish

• The?ray-finned fish, also known as class Actinopterygii, have?skeletons made of bone, and?fins supported by rays, or spines, of?bone
• The?scales?covering the bodies of the ray-finned fish vary in shape and composition
• Oxygen is gained via?diffusion from the water into the gills, which are covered by a gill flap called the?operculum
• During reproduction, eggs and sperm are released into the water and?fertilisation?takes place outside the body; this is?external fertilisation
• Their entire?life cycle?is?aquatic
• Body temperature is not regulated?but changes with the surrounding environmental temperatures
• Buoyancy is regulated by inflating and deflating an internal air sac called a?swim bladder

Ray-finned fish have a skeleton of bone, fins with bone rays, a swim bladder, and a gill operculum

Amphibians

• This class includes animals such as?frogs, toads, and?salamanders
• Amphibians have?soft, moist skin
• Amphibian skin is?permeable, enabling exchange of gases while under the water
  • Simple lungs are also present for gas exchange on land

   

• During reproduction, fertilisation is?external
• Jelly-like eggs?must be laid in water, and the?larval stage of the life-cycle is aquatic?e.g. frog tadpoles
  • Larvae such as tadpoles mature into an adult body form
  • Adult amphibians often leave the water and spend most of their time on land
  • There are a few exceptions to this; some frog and toad species can lay eggs on land which hatch into tiny adults rather than tadpoles
• Body temperature is?not regulated

The amphibian life-cycle includes an aquatic larval stage, and a terrestrial adult stage

Reptiles

• This class includes animals such as?lizards,?snakes, and?turtles
• Reptiles have?impermeable, scaly skin?made of keratin protein
• Reptiles are mainly?terrestrial, gaining their oxygen through highly folded surfaces in their?lungs
• During reproduction, male sperm is deposited inside the female's body, so fertilisation is?internal
• The eggs of reptiles are?soft-shelled
• Reptile body temperature is?not regulated

Reptiles have a body covering of scales, and breathe using highly folded lungs

Birds

• This class includes animals such as?chickens?and?ostriches
• Skin is covered with?feathers?made of keratin
• The front limbs of birds are modified into?wings, and?skeletons are lightweight, both adaptations for?flight
• Birds gain oxygen via a pair of?lungs?and connected?air sacs
• Fertilisation is?internal
• The eggs of birds are?hard-shelled
  • Shells contain calcium carbonate
• Bird?body temperature is?regulated, so is often warmer than the surrounding environment

Birds are usually highly adapted for flight and reproduce using internal fertilisation

Mammals

• This class includes animals such as?elephants,?humans,?and?whales
• Skin is covered with?hair?made of keratin
  • In some mammals body hair is lost in adulthood, e.g. in aquatic mammals
• Mammals gain oxygen via a pair of?lungs
• Fertilisation is?internal
• The young of mammals develops?inside the body?of the mother, and?live young?are born
  • There are some unusual exceptions to this e.g. the duck-billed platypus and the echidna
• Young mammals are fed on?milk?produced in?mammary glands
• Mammal?body temperature is regulated

Vertebrate Features Table