Concepts in Science - Kingdom Animalia

Kingdom Animalia

• Multicellular organisms with eukaryotic cells lacking cell walls, plastids, and photosynthetic pigments.
• Nutrient intake primarily through ingestion followed by internal digestion; some absorb nutrients without an internal digestive system.
• Exhibit sophisticated tissue differentiation and organization.
• Reproduction is primarily sexual; haploid cells are generally limited to gametes, except in some lower phyla.
• Phyla to be surveyed: Cnidaria, Platyhelminthes, Annelida, Arthropoda, and Chordata.

Phylum Cnidaria

• Includes approximately 10,000 living species.
• Named for cnidocytes, specialized cells containing nematocysts (stinging structures).
• Nematocysts are used to immobilize prey.
• Exclusively aquatic, predominantly marine.
• Includes jellyfish, sea anemones, sea fans, corals, and hydras.
• Two basic body forms:
  • Polyp: Tubular, closed at one end, with a mouth surrounded by tentacles at the other end (e.g., Hydra).
  • Medusa: Umbrella-shaped, jelly-like, free-swimming.

Phylum Platyhelminthes

• Dorso-ventrally flattened, commonly known as flatworms.

• Some species are parasites of humans (e.g., tapeworms).

• Tapeworms:

  • Inhabit the intestines of vertebrates.
  • Possess adaptations for attachment to the host, such as hooks and suckers in the head region.

• Planarians:

  • Common freshwater organisms found in ponds and streams.
  • Non-parasitic representatives of Platyhelminthes.

• Flukes:

  • Resemble planarians but are parasitic (e.g., liver flukes).
  • Complex life cycles, living in multiple hosts.
  • Oral sucker for attachment to the host.

Phylum Nematoda

• Worms with long, cylindrical bodies, commonly known as roundworms.
• One of the largest animal phyla; estimated to include around 500,000 species.
• Mostly free-living in soil; many are parasites of plants and animals.
• Ascaris lumbricoides:
  • Human parasite living in the digestive tract.
  • Males and females live in the intestines, feeding on intestinal contents.
  • Eggs are passed out with feces and can contaminate food, infecting new hosts.
  • Larvae hatch in the intestine and burrow through the walls, migrating to the lungs via the bloodstream.
  • In the lungs, they burrow through alveoli, crawl up the trachea, and down the esophagus.

Phylum Annelida

• Segmented worms, including earthworms, clamworms, and leeches.
• Body consists of a series of fused rings (segments), providing mobility and flexibility.
• Segmentation is the defining characteristic (Latin annulus = little ring).
• Diverse ecology:
  • Earthworms are herbivorous.
  • Clamworms are carnivorous.
  • Leeches consume blood.

Phylum Arthropoda

• Most biologically successful animal group.
• Largest animal phylum, including spiders, ticks, mites, scorpions, centipedes, millipedes, shrimp, crabs, and insects.
• Over one million known species, making up more than three-quarters of all known animal species.
• Found in virtually every habitat: flying, swimming, burrowing, and crawling.
• Occur in fresh and salt waters, deserts, the Arctic and Antarctic, tropical rainforests, and hot springs.
• Success attributed to:
  • Rigid external skeleton.
  • Jointed appendages (arthro = jointed; poda = foot) used for locomotion, feeding, reproduction, defense, and sensing the environment.
• Arachnids:
  • Spiders, scorpions, ticks, and mites.
• Crustaceans:
  • Predominantly aquatic, including lobsters, crabs, and barnacles.
• Insects:
  • Grasshoppers, butterflies, moths, hymenoptera (ants, bees, wasps), beetles, fleas, etc.
  • Most successful animal group and arthropod group.
  • Articulated (jointed), tracheated (tracheal tubes for gas exchange), and hexapod (six legs).

Phylum Chordata

• Defined by five major features:
  • Dorsal, hollow nerve cord (becomes the brain and spinal cord in mammals).
  • Notochord: Cartilaginous rod dorsal to the primitive gut in the embryo, acting as a cellular hydroskeleton. Persists throughout life in lower chordates; becomes the soft center of intervertebral discs in vertebrates.
  • Pharyngeal pouches: Paired pouches in the pharynx during some life stages. Form gill slits in aquatic chordates; present only during embryonic development in higher chordates.
  • Iodine-concentrating gland (or tissue).
  • Postanal tail.
• Three subphyla:
  • Tunicata (sea squirts): Larval stage resembles a tadpole; simple adult body with incurrent and excurrent siphons.
  • Cephalochordata (lancelets): Possess all chordate characteristics.
  • Vertebrata: Possess an endoskeleton of a skull and backbone (vertebral column).
• Classes within Vertebrata:
  • Agnatha (e.g., lampreys): Jawless vertebrates, parasitic on fish.
  • Pisces (fish).
  • Amphibia: Three orders: Urodela (retain tail in adulthood), Anura (no tail in adulthood), and Apoda (legless, burrowing).
  • Reptilia: Snakes, lizards, turtles, crocodiles, and dinosaurs.
  • Aves (birds): Diverse ecological roles, sizes, and behaviors; specific mating rituals.
  • Mammalia: Differentiated by external appearance, limb structure, locomotion, and teeth characteristics.
    • Unique external characteristics:
      • Hair at some time during development (though some have lost it through evolution, e.g., whales with insulating blubber).
      • Female mammals possess mammary glands with external openings for nourishing young.
    • Three major groups:
      • Monotremes: Lay eggs (e.g., echidna and platypus).
      • Marsupials: Brief gestation period followed by birth of tiny, underdeveloped offspring that complete development attached to the mother’s nipples (in a pouch - marsupium) (e.g., kangaroos).
      • Eutherians (Placental Mammals): Embryo nurtured by placenta; umbilical cord attaches fetus to placenta for gas and nutrient exchange and waste removal (e.g., humans).