zoology module 3

• Vertebrates


  Animals with backbones
• Subphylum of chordata


  One of the best known groups of animals, includes classes like Agnatha, Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves, and Mammalia
• The vertebral column was not present in the first vertebrates, which probably had only a notochord
• Notochord


  Flexible rodlike structure of mesodermal cells
• Vertebrate


  • Distinct head, with a differentiated tubular brain and three pairs of sense organs (nasal, optic, and otic)
  • Adapted to life underground, on the surface, and in the air
  • Feed upon plants, invertebrate animals, and one another
• Major groups of vertebrates based on morphology

  • Cyclostomes (jawless fishes)
  • Chondrichthyes (cartilaginous fishes)
  • Teleostomes (bony fishes)
  • Tetrapods
• Cyclostomes


  Include two classes of living, jawless fishes (agnathous) - Petromyzontiformes (lamprey eels) and Myxiniformes (hagfishes)
• Cyclostomes


  • Hagfishes are totally marine, often living in deep waters associated with muddy bottoms
  • Lampreys may be marine as adults but spawn in fresh waters, where the larvae spend some time before metamorphosing to the adult
  • Without lateral fins, lampreys swim by undulations of the body and can control direction only for short distances
• Chondrichthyes


  Class of jawed fish that contains the cartilaginous fish or chondrichthyians, which all have skeletons primarily composed of cartilage
• Chondrichthyes


  • Aquatic vertebrates with paired fins, paired nares, placoid scales, conus arteriosus in the heart, and a lack of opecula and swim bladders
• Teleostomi


  Obsolete taxon of jawed vertebrates that supposedly includes the tetrapods, bony fish, and the wholly extinct acanthodian fish
• Teleostomes


  • Key characters include an operculum and a single pair of respiratory openings, features which were lost or modified in some later representatives
  • Include all jawed vertebrates except the chondrichthyans and the extinct class Placodermi
• Agnaths


  • Predatory, the lampreys being well known for attacking salmonoid fishes
  • Lamprey attaches to its prey using its round, suctorial mouth, and it rasps a hole through the outer tissues using a tongue armed with keratinized teeth
  • Hagfishes feed somewhat similarly, but on a variety of prey—invertebrates (worms and soft-bodied forms) and dead fishes
• Chondrichthyans


  Include sharks, skates, rays, and chimaeras
• Chondrichthyans


  • Usually marine, but some sharks have entered fresh waters (the Amazon) or even live there permanently (Lake Nicaragua)
  • Herbivorous sharks are unknown
  • Sharks swim by undulations of the tail, but rays "fly" through the water by undulations of the pectoral fins
  • Most species occur in near-shore waters, but some range widely throughout the oceans
  • A few are found in deep water
• Teleostomes


  Osteichthyian fishes (those having an internal bony skeleton), can be divided into two groups: the subclasses Actinopterygii (ray-finned fishes) and Sarcopterygii (lobe-finned fishes)
• Sarcopterygii


  • Include the lungfishes, which live in marshes, ponds, or streams, and are frequent air breathers
  • Lay fairly large eggs, with a limited amount of yolk, that are enclosed in jelly coats like those of an amphibian
  • Larvae have external gills to supplement oxygen intake
• Actinopterygian fishes


  The common bony fishes of modern aquatic environments
• Actinopterygian fishes


  • Large species (sturgeons) are found in fresh waters (several other large species are found in the Amazon) as well as in marine environments
  • Diet may include plants, animals, and carrion
  • Most species are midwater swimmers, but many spend much time lying on the bottom
  • Tail, pectoral, and even dorsal fins are used in swimming
  • Reproduction is by way of large numbers of small eggs, which produce small larvae or develop directly to the adult
• Tetrapods


  Any four-limbed vertebrate animal of the superclass Tetrapoda, including all extant and extinct amphibians and amniotes
• Tetrapods


  • Live primarily on land and are rather similar in habit
  • Members include the amphibians, reptiles, birds, and mammals
  • Amphibians are widespread in the warmer parts of the continents, being absent only in the far north and in the Antarctic
  • Three orders are recognized: Candata (the salamanders), the frogs and toads (Anura, or Salientia), and the Apoda or Gymnophiona (caecilians)
  • Modification takes many forms, from the moist glandular skin (some scale remnants persist in apodans) to the loss of many of the bones of the skull
  • Like their ancestors, amphibians are cold-blooded and tend to be aquatic or limited to moist surroundings
  • Salamanders are seemingly the least modified in body form, do not actively pursue prey and at best are only marginal swimmers
  • Frogs and toads hop using hind-limb propulsion and the forelimbs as body props
  • Burrowing, wormlike apodans are without limbs
• Vertebrate evolution


  • Evolution of the notochord, dorsal nerve tube, and pharyngeal slits in chordate structure suggests improved swimming capability and probably greater ability to capture prey
  • Specialization in the vertebrate for the active capture of larger prey is evident both in the structure of the mouth and in the relatively simple structure of the pharynx, with its strong gill development
• Vertebrate skeletal system


  • Support and protection are provided by the exoskeletal and endoskeletal divisions
  • The exoskeleton, when present, is basically protective but functions in tooth support in the mouth region
  • The endoskeleton protects the brain and spinal cord and assists primarily with locomotion in the trunk and tail regions
  • The endoskeleton begins as cartilage and may remain so or may develop into bone
  • The cartilaginous endoskeleton, found in the shark or chimaerid, is usually calcified so as to be stiffer and stronger
  • Bone is distinctive but highly variable; some types of bone contain cells, others do not, or the bone may be laminar, spongy, or arranged in sheathing layers around blood channels
• Vertebrate tissues and muscles

  • Tissue development in the vertebrate is unique in its complexity; tissues in the strict sense (defined as a mass or sheet of similar cells with a similar function), however, do not exist
  • The simplest situation is seen in the epidermis, but even here there is a layered system in which different cell types provide different functions (such as protection and secretion)
  • The stratified epithelium of the vertebrate is highly characteristic of that group (a similar one is seen in only one invertebrate group, the class Chaetognatha)
• Vertebrate nervous system and organs of sensation

  • The dorsal position, tubular structure, and epidermal origin of the central nervous system are definitive of the chordates
  • The sensory structures are distinctive of the chordates and include the paired nasal, optic, and otic organs (along with the strongly differentiated head)
• Vertebrate digestive system


  • The mouth and pharynx can be considered as parts of this system; the latter as an expanded cavity in the head is unmatched in any other group
  • The stomach and gut have distinctive structures
• Vertebrate excretory system


  • The excretory system is unique in its nephrons, which filter the blood in the glomeruli and remove a variety of wastes from the body through selective secretion and reabsorption
  • In the shark or the coelacanth Latimeria, urea is used to raise the osmotic pressure of the blood to that of the marine habitat, thus saving these organisms considerable metabolic energy
  • The large intestine (sometimes centred in a rectal gland) acts as an auxiliary excretory organ, as do also the gills of fishes or the sweat glands of mammals
• Vertebrate respiration and gas exchange

  • Respiration involves specialized body structures, such as lungs or gills, but also can involve other areas, such as the skin itself
  • Respiration involves exchange of gases both between the body of the organism and the environment and between the blood system and the body tissues
  • It also involves cellular respiration where oxygen is used and carbon dioxide is produced
  • There is nothing characteristic of the vertebrate in this functional area; even the hemoglobin of the blood is suggested in the respiratory pigments of other animals
• Vertebrate circulatory system


  • The circulatory system of vertebrates is closed in that fluids course through vessels, but there is free movement of cells in and out of blood
  • Some leukocyte (white blood cell) movement out of the capillaries and fluid leakage are observed in all tissues
  • Blood tissues are distinctive in the range of specialized cells, although these vary in detail among animals
  • The immune function of the blood is best developed in the vertebrate
• Vertebrate endocrine system


  • Characterized by its separate organs
  • The occurrence of a pituitary or a thyroid gland is suggestive of the evolutionary change and specialization that took place within this group
  • The relatively unspecialized nature of some parts of this system is seen in certain scattered cells in the gut wall or even the clumps of islet cells of the pancreas
• The ancestral vertebrate (protovertebrate) has been sought for more than 100 years, and the likelihood of finding it today is not much greater than in the past
• It can be assumed that the protovertebrate was small and soft-bodied, two factors that suggest the improbability of finding a fossilized form in a recognizable condition
• There are Cambrian fossils that have been suggested to be fossil cephalochordates and there are scales of agnath fishes, but the first type of fossil is too simple and the second already too complex to explain the transition
• Biodiversity loss is a decrease in biodiversity within a species, an ecosystem, a given geographic area, or Earth as a whole
• the nervous system is made up of the central nervous system (CNS) which includes the brain and spinal cord, and the peripheral nervous system (PNS)
• SUBPHYLUM VERTEBRATA (OR CRANIATA)

  • Bilaterally symmetrical
  • Internal skeletal support with skull enclosing a highly developed brain and a vertebral column and nerve cord
  • Paired, jointed appendages
  • Skin
  • Advanced organ systems
  • Sense organs concentrated in head
• Class Agnatha (hagfishes, lampreys)


  • Primitive
  • Jawless
  • Paired fins are poorly developed or lacking
  • Rasping tongue
  • Notochord without bone
  • Skin is soft, glandular, and slimy
  • True gill arches absent
  • Marine habitat
• Class Placodermi (placoderms)


  • Extinct
  • Fishlike
  • Jaws supported by both cranium and hyoid arch (amphistylic)
  • Partly ossified cranium
  • Primitive
  • Head and trunk have armour that is jointed at the neck
  • Pelvic fins present or absent
  • Pectoral fins or finlike structures often present
  • Gill arches
• Class Chondrichthyes (sharks, rays, and skates)

  • Cartilaginous fishes
  • Jaws
  • Paired fins
  • No swim bladder
  • Pelvic fins in males often modified to form claspers
  • Gill arches internal to gills
  • Reduced notochord
  • Lateral-line system
  • Paired nostrils
  • Internal nares absent
  • Separate sexes
  • Internal fertilization and direct development
  • Oviparous, ovoviviparous, or viviparous
• Subclass Elasmobranchii (sharks and rays)

  • Numerous teeth derived of placoid scales
  • 5 to 7 gill clefts
  • Operculum absent
  • Cloaca
  • Upper jaw not fused with braincase
  • Dorsal fin nonerectile
  • With spiracles
  • Worldwide distribution