Animal Phyla and Characteristics Study Notes

Overview of Animal Phyla and Characteristics

General Animal Characteristics

  • Nervous system classification:
    • No nerves: Refers to primitive organisms
    • Nerves: Found in more complex organisms
  • Body Symmetry:
    • Radial symmetry: Organisms can be divided into similar halves by any longitudinal cut through the center (e.g., Echinoderms)
    • Bilateral symmetry: Organisms can only be divided into similar halves by a single longitudinal cut (e.g., Protostomes and Deuterostomes)
  • Colonial choanoflagellate ancestor: Suggests a common evolutionary ancestor for most animals

Major Animal Phyla

Phylum Porifera (Sponges)
  • Aquatic, sessile organisms
  • Lack true tissues and organs
Phylum Cnidaria (Jellyfish, Corals)
  • Simple organisms with radial symmetry
  • Possess specialized cells called cnidocytes
Phylum Platyhelminthes (Flatworms)
  • Bilateral symmetry and three tissue layers
Phylum Echinodermata (Radially Symmetrical Marine Animals)
  • Existing Species: Approximately 6,500
  • Examples: Sea stars, sea urchins, sand dollars, sea cucumbers
  • Body Plan:
    • Adults are radially symmetrical; larvae exhibit bilateral symmetry
    • Likely derived from bilaterally symmetrical ancestors that reverted to a more primitive form due to slow movement (cephalization offers no advantage)
  • Internal Structure:
    • Endoskeleton composed of calcium plates for support and protection
    • Projections through skin in some species
  • Gas Exchange:
    • Sea stars have small gills that extend from the body
    • Sea cucumbers have an internal respiratory tree
  • Reproduction and Systems:
    • Reproduce sexually
    • Possess a simple circulatory system but lack true respiratory and excretory systems
Phylum Rotifera
  • Microscopic, aquatic organisms
Phylum Mollusca
  • Includes organisms with a soft body, often protected by a hard shell (e.g., snails, clams)
Phylum Annelida (Segmented Worms)
  • Have segmented bodies and a true coelom
Protostomes vs. Deuterostomes
  • Protostomes: Organisms in which the mouth develops before the anus during embryonic development (e.g., Arthropoda, Mollusca)
  • Deuterostomes: Organisms in which the anus develops before the mouth (e.g., Echinodermata and Chordata)
Phylum Nematoda (Roundworms)
  • Unsegmented worms with a complete digestive system
Phylum Arthropoda
  • Includes insects, arachnids, and crustaceans; characterized by a chitinous exoskeleton and jointed appendages

Phylum Chordata (The Chordates)

Common Characteristics
  • Dorsal hollow nerve cord: Present at some point in life
  • Notochord: A dorsal supporting rod
  • Gill slits: Present near the throat region
  • Bilateral symmetry: With a ventral heart
  • Body extends past the anus to form a tail: Some features only appear in early embryonic development, reflecting ancestral evolutionary relationships
Early Chordates
  • Tunicates (Class Urochordata): Marine animals that display features of chordates in their larval stage
  • Lancelets (Class Cephalochordata): Small marine animals with chordate characteristics throughout their lives
Groups of Vertebrates
  • Agnatha (Jawless Vertebrates):
    • Few species remain, including lampreys and hagfish
    • Lampreys: External parasites; lack jaws and paired fins
    • Hagfish: Primarily scavengers
  • Class Chondrichthyes (Cartilaginous Fish):
    • Include sharks and rays
    • Endoskeleton: Composed of cartilage instead of bone
    • Movement: Rays and skates use enlarged pectoral fins; sharks use tail and pelvic fins for swimming
    • Reproduction: Females are ovoviviparous, retaining fertilized eggs internally
  • Class Actinopterygii (Bony Fish):
    • Over 30,000 species, skeletons start as cartilage and become bony in adults
    • Scales: Protect the body
    • Operculum: Covers and protects gills (4-5 pairs) and acts in water movement for breathing
    • Swim Bladders: Aid in depth regulation through gas concentration management
  • Class Amphibia:
    • Includes frogs, toads, and salamanders (approx. 4,000 species)
    • First vertebrates to adapt to land 300 million years ago
    • Require moist environments for egg retention; undergo metamorphosis from aquatic larvae to air-breathing adults
    • Heart: Frogs possess a three-chambered heart with mixed blood (oxygenated and deoxygenated)
    • Gab exchange can occur through skin but limits sustained activity due to oxygenation issues
  • Class Reptilia:
    • About 7,300 species, including turtles, lizards, and snakes
    • Adaptations support terrestrial living, including waterproof egg shells and tough skin
    • Need to retain moisture via concentrated kidney urine and large lung structures
    • Heart structure evolved to improve blood oxygenation separation, allowing for higher muscular activity
    • Snakes evolved from lizards and have adaptations for movement
  • Class Aves (Birds):
    • 8,700 species; share features with reptiles, such as scales on their legs
    • Endothermic, can maintain constant high body temperature; enables rapid movement
    • Wings evolved from forelimbs for flight, with specialized feathers providing insulation and lift
    • Four-chambered heart efficiently circulates gases; incubation of eggs relies on heat from parents
  • Class Mammalia:
    • Approximately 4,500 species sharing common characteristics:
    • Body covered in hair
    • Four-chambered heart
    • Mammary glands for milk production
    • Specialized teeth for varied diets
    • Endothermic organisms with long gestation periods
    • Divided into three groups:
    • Monotremes: Eggs laid (e.g., platypus)
    • Marsupials: Young complete development in a pouch (e.g., kangaroos)
    • Placentals: Young develop in utero before birth, occupying diverse environments.

Homework

  • Complete problems 1-10 on page 107 for further review of topics discussed.