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Animal classification [part 2]
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Animal classification [part 2]


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  • 2. TOPIC OUTLINE A) Some general features of animals B) Evolution of the animal body plan C) Cnidaria D) Platyheminthes E) Annelida F) Arthropoda G) Mollusca H) Echinodermata I) Chordata
  • 3. PHYLUM ARTHROPODA Class: Insecta/ Hexapoda bee Class: Arachnida spiders Subphylum: Crustacea water flea Daphnia, prawns, barnacles, crabs, lobsters, woodlice Daphnia Barnacles
  • 4. Phylum Arthropoda contains more species than any other phylum 80%  ~ 1 million arthropod species described  ubiquitous habitats [exist everywhere]
  • 5. Phylum Arthropoda The class insecta / hexapoda is the largest class.
  • 6. 1st major innovation in body structure among coelomates Segmentation among annelids: The development of jointed appendages : an even more profound innovation Jointed appendages mark the origin of the body plan characteristic of the most successful of all animal groups.
  • 7. include: Jointed appendages : legs antennae mouthparts are used for a variety of functions: feeding, locomotion and sensory purposes the functional flexibility provided by such a broad array of appendages has made arthropods the most successful of animal groups
  • 8. Arthropod bodies are segmented like those of annelids  the individual segments:  often exist only during early development  fuse into functional groups as adults Head: 5-7 segments Thorax: 3 segments Abdomen: 11 segments
  • 9. Specialisation of body parts: Tagmata the arthropod body has undergone various forms of regional specialisation to produce segment groups specialised for different functions these specialised body regions are called tagmata (singular, tagma) (e.g. the head, thorax and abdomen) this fusing process is known as tagmatization, is of central importance in the evolution of arthropods
  • 10. the head possesses sensory receptors:  eyes  antennae  feeding appendages  the brain is much larger than in annelids  cephalisation is much more pronounced
  • 11. Question: SEP 2013 Paper 2 Use your knowledge of biology to explain the evolutionary importance of the following: tagmatisation in insects. (5)
  • 12. Exoskeleton  is secreted by the epidermis  contains chitin, a nitrogen-containing polysaccharide which resembles cellulose
  • 13. Exoskeleton  chitin has high tensile strength (it is difficult to break by pulling from both ends)  the properties of the exoskeleton can be altered by the addition of other chemicals like in crustaceans, calcium salts makes it harder  a range of hardness, flexibility and stiffness is thus possible  flexibility is important at joints
  • 14. Advantages of the exoskeleton: 1. support, particularly on land; 2. it provides an anchor for the muscles internally; 3. protection from physical damage; 4. addition of a layer of wax from special glands in the epidermis helps prevent desiccation on land; 5. insect flight and the jumping ability of fleas and grasshoppers depends on the presence of a remarkably elastic protein in the exoskeleton; 6. it has a low density, which is important for flying animals; 7. flexible joints are possible between segments; 8. it can be modified to form hard jaws for biting, piercing, sucking or grinding; 9. it can be transparent in places allowing, for example , entry of light into eyes and camouflage in water.
  • 15. TWO disadvantages associated with the exoskeleton: Final body size is limited:  either not be able to support its own weight  or the exoskeleton would have to be so massive that it would not be able to move An arthropod the size of an elephant would: [The other important restriction on size of insects is their breathing mechanism which works mainly by diffusion through tube called tracheae]
  • 16. It restricts growth:  so periodic moulting (ecdysis) is required if the animal is to grow  however, the arthropod is very vulnerable to attack by predators at this period
  • 17. The haemocoel
  • 18. Coelom is a reduced in : arthropods Their main body cavity is the: haemocoel molluscs
  • 19.  develops from the cavities of the blood vascular system and is therefore filled with blood  the blood is generally circulated in the haemocoel, and through several attached blood vessels  the major organs are bathed in blood The haemocoel
  • 20.  the coelom still exists but is:  small  confined to cavities of excretory organs and the reproductive ducts the high blood volume to body volume in arthropods enables them to maintain a high metabolic rate, allowing them to be very active animals
  • 21. Flight  in insects have greatly increases opportunities for: finding food escaping predators
  • 22. Cleidoic egg  egg with a relatively impermeable shell  is an adaptation to conserve water as it prevents loss of moisture  also found in birds and reptiles  shell is porous to air  shell may be flexible or calcerous  it frees the animal from returning to water to lay eggs
  • 23. Question: MAY 2012 Paper 2 Use your knowledge of biology to explain the evolutionary importance of the following: the cleidoic egg. (5)
  • 24. Main features of the Arthropoda (Arthropods) 1. Triploblastic, coelomate. 2. Metameric segmentation as in annelids but segments not separated from each other by septa, definite in number, and showing varying degrees of specialisation. 3. Bilateral symmetry. 4. Exoskeleton of chitin. 5. Each segment typically bears a pair of jointed appendages used for locomotion or feeding or sensory purposes. 6. Coelom much reduced, main body cavity a haemocoel. 7. Some groups have a compound eye for vision. 8. Cuticle shed periodically (moulting or ecdysis) to allow for growth. [diagnostic features: Exoskeleton; jointed appendages]
  • 25. Main features of the class Insecta (Insects) 1. Mainly terrestrial. 2. Well-defined head, thorax and abdomen. 3. One pair of antennae.
  • 26. Main features of the class Insecta (Insects) 4. Usually three pairs of mouthparts. 5. A pair of compound eyes and simple eyes. 6. Three pairs of legs on thorax, one pair per segment. Usually one or two pairs of wings on thorax. 7. Life cycle commonly involves metamorphosis either ‘complete’ or ‘incomplete’, with a larval stage. 8. No gills in adult. Gaseous exchange by tracheae
  • 27. Subphylum: Crustacea Spider crab Can weigh 19 kg.
  • 28. 1. Mainly aquatic. 2. Cephalothorax (head and thorax not distinctly separate). Main features of the subphylum Crustacea (Crustaceans)
  • 29. A crustacean Carcinus maenas, the shore crab. Dorsal view.
  • 30. Main features of the subphylum Crustacea (Crustaceans) 3. Two pairs of antennae. 4. At least three pairs of mouthparts. 5. A pair of compound eyes raised on stalks. 6. Appendages often modified for swimming, as they are mainly aquatic; number of legs variable, sometimes 10. 7. Larval form occurs. 8. Typical gaseous exchange by gills – outgrowths of the body wall or limbs. 9. Dorsal side of body usually protected by a shield-like carapace.
  • 31. Main features of the class Arachnida (Arachnids) 1. Terrestrial. 2. Cephalothorax; thorax separated from abdomen by a narrow waist-like constriction (pedicel). Spider pedicel
  • 32. 3. No antennae. Spider – dorsal view.
  • 33. 4. No true mouthparts but one pair of appendages used in capturing prey and one pair of sensory palps. 5. Simple eyes only (no compound eyes). 6. Four pairs of walking legs. 7. No larval forms. 8. Gaseous exchange by book lungs or tracheae.
  • 34. Question: MAY 2007 Paper 2 “Arthropods are considered to be the most successful animals on Earth”. Discuss. (25)
  • 35. Question: SEP 2002 Paper 2 Why are insects the most successful animals on Earth? Insects are successful animals as they have various adaptations to conserve water thus enabling them to inhabit a terrestrial environment. They excrete uric acid which does not require water for its elimination, from the Malpighian tubules. Their exoskeleton is covered by a thin layer of wax, making it waterproof. Their spiracles are guarded by valves, which close to reduce water loss from the tracheal system when the insect is at rest. Hairs at the spiracle have the same role. Embryos are enclosed in a relatively impermeable shell (cleidoic egg), allowing development outside the body without loss of water. They have diverse mouthparts allowing them to feed on solid or liquid food, thus reduce competing for food. Some possess wings which are an asset both to escape predators and to find a mate or new locations with bountiful resources.
  • 36. Question: SEP 2005 Paper 2 Use your knowledge of biology to explain the following statement. Scorpions and woodlice have very different appearances, yet are classified in the same phylum. (5)
  • 37. TOPIC OUTLINE A) Some general features of animals B) Evolution of the animal body plan C) Cnidaria D) Platyheminthes E) Annelida F) Arthropoda G) Mollusca H) Echinodermata I) Chordata
  • 38. Slow-moving snails and slugs Relatively sedentary bivalves such as clams Highly active cephalopods (cuttlefish, squid, octopus)Types of molluscs
  • 39. PHYLUM MOLLUSCA Class: Gastropoda slugs snails limpets
  • 40. Mollusca: 2nd largest animal phylum  with almost 100 000 species the giant squid is the largest non-vertebrate animal:  weighs several tonnes  measures 16 m in length
  • 41. Molluscs were able to colonise : aquatic & terrestrial environments by : The more active molluscs show a reduction or loss of the shell because: 2. The formation of a protective shell 1. The use of gills for gaseous exchange A shell hinders locomotion.
  • 42. Body plan of the Mollusca bilateral symmetry Visceral mass:  is covered with a soft epithelium  contains the organs of:  digestion  excretion  reproduction A muscular foot that is used in locomotion
  • 43. Molluscs may have a differentiated head at the anterior end of the body: octopus The muscular foot may be adapted for:  locomotion  attachment  food capture (in squids & octopuses)
  • 44. The mantle :  is a thick epidermal sheet that covers the dorsal side of the body  bounds the mantle cavity
  • 45. The mantle : Secretes the calcium carbonate of the shell in those molluscs with a shell
  • 46. The mantle cavity has a role in breathing: Terrestrial molluscs: the mantle cavity forms a lung sac Aquatic molluscs: the gills or ctenidia project into the mantle cavity
  • 47. Ctenidia consist of filaments rich in blood vessels:  greatly increase the surface area  capacity for gas exchange mollusc gills are very efficient  can extract 50% or more of the dissolved oxygen from the water that passes through the mantle cavity
  • 48. this water:  brings in oxygen and, in the case of the bivalves, food;  carries waste materials and gametes in aquatic molluscs, a continuous stream of water passes into and out of the mantle cavity, drawn in by the cilia on the gills
  • 49. Locomotion some molluscs e.g. slugs secrete mucus, forming a path that they glide along on their foot in cephalopods (squids and octopuses) the foot is divided into arms, also called tentacles  in some pelagic forms (molluscs that are perpetually free- swimming), the foot is modified into wing-like projections or thin fins
  • 50. Feeding the radula:  a rasping, tongue-like organ used for feeding  one of the most characteristic features of all the molluscs except the bivalves radula food Scraps of food
  • 51.  dozens of microscopic, chitinous teeth arranged in rows The radula consists primarily of : gastropods use their radula to: Scrape algae & other food materials off their substrates … then to convey this food to the gut
  • 52. Circulation the circulatory system of all molluscs except cephalopods consists of:  a heart  an open circulation Cephalopods: a closed circulatory system aids their active form of life
  • 53. The coelom is primarily represented by a small cavity around the heart Coelom
  • 54. Main features of the Mollusca 1. Bilaterally symmetrical. 2. Unsegmented, triploblastic coelomates. 3. Body soft and fleshy and divided into a head, ventral muscular foot and dorsal visceral hump. 4. The mantle secretes a calcereous shell. 5. Main body cavity is the haemocoel. 6. No limbs. 7. Gaseous exchange effected by one or more pair/s of ctenedial gills housed in the mantle cavity. [Diagnostic feature: Body soft and fleshy and divided into a head, ventral muscular foot and dorsal visceral hump.]
  • 55. Main features of the class Gastropoda 1. Terrestrial, marine and freshwater. 2. Asymmetrical. 3. Shell of one piece, usually coiled due to rotation of hump during growth.
  • 56. Main features of the class Gastropoda 4. Large flat foot used in locomotion. 5. Head, eyes and sensory tentacles. 6. Radula, a rasping tongue-like structure used in feeding. 7. Anus at anterior.
  • 57. Operculum :  a plate present in most marine gastropods that the animal can pull to close the shell  most adult land gastropods  most gastropods have a pair of tentacles with eyes  these tentacles have been lost in some of the more advanced forms of the class EYE
  • 58. TOPIC OUTLINE A) Some general features of animals B) Evolution of the animal body plan C) Cnidaria D) Platyheminthes E) Annelida F) Arthropoda G) Mollusca H) Echinodermata I) Chordata
  • 59. Phylum: Echinodermata deuterostomate, triploblastic animals have no proper circulatory system Class: Asteroidea (starfish e.g. Asterias) Class: Echinoidea (sea urchins e.g. Echinocardium
  • 60. all marine are largely bottom-dwellers (benthic) inhabiting shorelines and shallow seas
  • 61. Echinoderm body plan  undergoes a fundamental shift during development  all echinoderms have secondary radial symmetry:  larvae are bilaterally symmetrical but adults become radially symmetrical
  • 62. Question: SEP 2012 paper 2 Use your knowledge of biology to explain the following statements echinoderms exhibit secondary radial symmetry. (5)
  • 63.  show pentamerous symmetry (a form of radial symmetry) Adult echinoderms have a five-part body plan
  • 64. Endoskeleton  ‘echinoderm’ means spiny skin  refers to an endoskeleton composed of hard calcium-rich plates just beneath the delicate skin  in adults, the plates frequently fuse, forming a hard shell
  • 65. The plates in certain portions of the body of some echinoderms are perforated:  tube feet, part of the water vascular system [a unique feature of this phylum] extend TS arm of starfish Tube feet
  • 66. Ossicles in the skin provide sessile animals with: support protection from predators + wave action Ossicles in starfish
  • 67. The water vascular system is a hydraulic system which aids in: Movement Respiration Excretion Feeding the water vascular system radiates from a ring canal that encircles the oesophagus
  • 68. Five radial canals extend into each of the five parts of the body and determine the basic symmetry Madreporite:  a sieve-like plate on the animal’s surface  location through which water enters the water vascular system and flows to the ring canal through a tube, or stone canal The five radial canals in turn extend out through short side branches into the hollow tube feet
  • 69. Suckers may be present at the end of each tube foot Modified tube feet around the mouth cavity of certain echinoderms are used in feeding
  • 70. Body cavity the coelom:  is connected with a complicated system of tubes  helps provide circulation & respiration the digestive system is simple but usually complete, consisting of : gut mouth anus coelom
  • 71. Reproduction many echinoderms are able to regenerate the lost part some echinoderms, especially starfish, drop various parts when under attack
  • 72. Reproduction in a few echinoderms, asexual reproduction takes place by splitting [Fragmentation]  the broken parts of sea stars can sometimes regenerate whole animals
  • 73. Reproduction most reproduction in the phylum is:  sexual  external sexes are separate [free-swimming – form part of plankton] Metamorphose into sedentary adults Male Female Fertilised egg Bilaterally symmetrical larva
  • 74. Main features of Echinoderms 1. Triploblastic, coelomate. 2. Skin contains calcareous ossicles (endoskeleton) and spines. 3. Exclusively marine. 4. Adult with five-rayed symmetry, but larva is bilaterally symmetrical. 5. Mouth generally on lower (oral) side; anus on upper (aboral) side. 6. A coelomic water vascular system which contains and is in direct contact with sea water and which operates hydraulically the locomotory tube feet (podia).
  • 75. 7. No proper circulatory system. 8. No differentiated head. 9. No excretory organs. 10. A through gut. 11. Sexes are separate. 12. Nervous system diffuse, decentralised, allowing them to engage in their environment equally from all sides. [Diagnostic features: pentamerous radial symmetry; tube feet]
  • 76. Characteristics of the Class Asteroidea (starfish) characterised by a flattened body which grades into 5 or sometimes more (up to 40) arms the animals are not attached and freely mobile few calcareous plates in body wall; movable spines
  • 77. Characteristics of the Class Asteroidea (starfish) Pedicellariae:  modified spines which act as scissors or forceps to remove organisms that try to settle down on their body surface
  • 78. Characteristics of the Class Asteroidea (starfish) starfish are mostly carnivorous digestion is mostly extracellular  anus has little function
  • 79. Main features of the Class Echinoidea (sea urchin) spherical, free-living echinoderms which lack arms numerous calcareous plates in the body wall, attached to each other to form a rigid test the test bears: pedicellariae movable spines
  • 80. Main features of the Class Echinoidea (sea urchin) the mouth bears a distinctive grazing apparatus, called Aristotle’s lantern used for chewing Teeth of Aristotle’s lantern
  • 81. Question: SEP 2005 Paper 2 Use your knowledge of biology to explain the following statement. Starfish and sea-urchins have very different appearances, yet are classified in the same phylum. (5)
  • 82. TOPIC OUTLINE A) Some general features of animals B) Evolution of the animal body plan C) Cnidaria D) Platyheminthes E) Annelida F) Arthropoda G) Mollusca H) Echinodermata I) Chordata
  • 83. Phylum: CHORDATA [Chordates] Sub phylum: Vertebrata Class: Osteichthyes / Teleosta (bony fish - teleosts) Class: Amphibia (amphibians: newts, salamanders, frogs and toads) Class: Reptilia (reptiles) Class: Aves (birds) Class: Mammalia (only this class in syllabus)
  • 84. Four principal features characterise chordates: • Notochord • Dorsal hollow nerve cord •Pharyngeal slits •Muscular, postanal tail.
  • 85.  runs just beneath the dorsal surface of the animal  hollow means it is filled with fluid  in vertebrates, the dorsal nerve cord differentiates into the: 1. A single, hollow nerve cord  brain  spinal cord
  • 86. 2. A flexible rod, the notochord is present at some stage in the life cycle in all chordates  forms on the dorsal side of the primitive gut in the early embryo
  • 87. during embryological development in most vertebrates by the vertebral column that runs around the nerve cord. The notochord becomes surrounded and then replaced
  • 88.  connect the pharynx, a muscular tube that links the mouth cavity and the gullet, with the outside  in most vertebrates, the slits do not actually connect to the outside and are better termed pharyngeal pouches 3. Pharyngeal slits
  • 89. pharyngeal pouches are:  present in the embryos of all vertebrates  but are lost later in the development of terrestrial vertebrates the presence of these structures in all vertebrate embryos provides a clue to the aquatic ancestry of the group.
  • 90. extends beyond the anus, at least during their embryonic development nearly all other animals have a terminal anus 4. The postanal tail
  • 91. All chordates have all four of these characteristics at some stage in their lives e.g. Human adults retain only the:  nerve cord  one pair of pharyngeal slits which are the Eustachian tubes that connect the throat to the middle ear Human embryos have all four features
  • 92. In addition to these four principal features, a number of other characteristics distinguish the chordates fundamentally from other animals:  chordates have a more or less segmented body plan, and distinct blocks of muscles can often be clearly seen in embryos of this phylum  most chordates have an internal skeleton against which the muscles work  either this internal skeleton or the notochord makes possible the extraordinary powers of locomotion that characterise the members of the group
  • 93. Main features of Chordates 1. Notochord present at some stage in the life history. 2. Post-anal tail (tail starts posterior to anus). 3. Bilateral symmetry. 4. Pharyngeal (visceral) clefts present (slits in the pharynx). 5. Dorsal, hollow nerve cord. 6. Triploblastic coelomate. 7. Segmental muscle blocks (myotomes) on either side of the body. 8. Limbs formed from more than one body segment. [diagnostic features : 1-4]
  • 94. Main features of the subphylum Vertebrata 1. Notochord replaced in adult by a vertebral column (backbone), a series of vertebrae made either of bone or cartilage. 2. Well-developed central nervous system including brain. Skull protects the brain. A high degree of cephalisation. 3. A living endoskeleton. 4. Pharyngeal clefts (gill slits) few in number. 5. Two pairs of fins or limbs. These are attached to the rest of the skeleton by girdles, pectoral and pelvic. 6. Closed circulatory system.
  • 95. Reptiles, birds and mammals: the amniotes possess extraembryonic membranes, including an amnion, during development Wastes are discharged into another sac called the allantois. The embryo obtains food from a yolk sac attached to its gut.
  • 96. Within the shell are several extraembryonic membranes that protect the embryo from drying and assist gas exchange and excretion of nitrogen.
  • 97. The pentadactyl limb  has five digits on the hand & foot  has a specific pattern of bones Penta = 5 Dactyl = Fingers
  • 98. The structure of a human arm includes A bone between the shoulder and the elbow: humerus. Below the elbow, are two other bones:  radius  ulna A set of wrist bones and then the five-digit fingers, follow. 1 2 3
  • 99. The pentadactyl limb is found in all classes of tetrapods The fundamental structures of pentadactyl limbs are the same in all tetrapods indicating that they originated from a common ancestor.
  • 100. But in the course of evolution these fundamental structures have been modified  they have become:  superficially different  unrelated structures  this phenomenon is shown in the forelimbs of mammals to serve different functions in adaptation to different environments & modes of life
  • 101. The pentadactyl limb is a homologous structure Homologous structures have the same basic plan but are adapted for different functions Basic pentadactyl pattern WalkingRunning Flying Swimming
  • 102. Question: MAY 2003 Write brief notes on the evolutionary significance of each of the following structures: [five marks] The pentadactyl limb Typical limb of the mammals, birds, reptiles, and amphibians. The limb has three parts a hand/foot with five digits (fingers/toes), a lower limb containing two bones, and an upper limb containing one bone. This basic pattern has persisted in all the terrestrial vertebrates, and those aquatic vertebrates (such as seals) which are descended from them. Natural selection has modified the pattern to fit different ways of life. In flying animals (birds and bats) it is greatly altered and in some vertebrates, such as whales and snakes, the limbs are greatly reduced or lost. Pentadactyl limbs of different species are an example of homologous organs.
  • 103. Main features of Mammalia 1. Skin bears hair with two types of glands, sebaceous and sweat. 2. Bony skeleton. 3. Two pairs of pentadactyl limbs. 4. Visceral clefts never develop gills. 5. External ear. 6. Only two genera lay eggs, the spiny anteater and the duck-billed platypus. 7. Embryo develops in mother. Young born in a more mature state, i.e. mammals are viviparous. 8. Mother has mammary glands which produce milk for the newborn. Internal fertilisation. 9. Muscular diaphragm. 10. Well-developed sense organs. 11. A highly developed brain and intelligent behaviour involving learning and memory. 12. Heterodont dentition (various types and sizes of teeth) 13. A bony roof to the mouth called the palate. 14. Endothermic.
  • 104. Question: MAY 2008 Paper 2 Use your knowledge of biology to describe the selective advantage of each of the following adaptations: viviparity (live birth) in mammals. (5)
  • 105. Evolutionary trends shown in vertebrates towards adaptation to a terrestrial mode of life Creatures that make the transition from life in water to life on land, must come to terms with FOUR new exigencies: they must 1. find ways to cope with gravity; 2. breathe air; 3. avoid desiccation; 4. evolve senses that are appropriate to air rather than water