Kingdom Animalia Part I

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10 Questions

How do nematodes rely on respiration, circulation, and excretion due to their small size?

diffusion of gases and wastes through their body wall

Which of the following is true about the nervous system of nematodes?

Consists of several ganglia but no brain

Which of the following nematodes is a human parasite that causes trichinosis?

Trichinosis Worms

Annelids have a closed circulatory system.

False

Molluscs have __________ inside the mantle cavity for respiration.

gills

Match the following mollusc classes with their characteristics:

Gastropods = Move by a single muscular foot and feed by a radula Bivalves = Filter feed through siphon and have two shells Cephalopods = May have a shell or not and feed with a powerful beak

What are the defining characteristics of all members of Kingdom Animalia?

Eukaryotic, multicellular, heterotrophic, lack cell walls

What is the largest kingdom in terms of number of species?

Animalia

What is the first type of symmetry observed in animals?

Radial symmetry

Flatworms are acoelomate organisms.

True

Study Notes

Kingdom Animalia

  • Members of Kingdom Animalia are eukaryotic, multicellular, heterotrophic, and lack cell walls
  • Largest kingdom, with 95% of species being invertebrates (lack a backbone) and 5% being vertebrates (have a backbone)
  • Cell specialization: cells become more specialized to perform specific functions
  • Development: growth of a single celled zygote into a complete organism
  • Three types of germ tissues form after gastrulation:
    • Ectoderm: becomes nerves, sense organs, and skin
    • Mesoderm: becomes muscles, circulatory, reproductive, and excretory systems
    • Endoderm: becomes digestive tract and respiratory system
  • Body symmetry:
    • Early animals have no symmetry
    • Radial symmetry appears first, with infinite lines of symmetry
    • Pentaradial symmetry has 5 lines of symmetry
    • Bilateral symmetry has only 1 line of symmetry and is the most advanced
  • Body cavity formation:
    • Early animals are solid with no body cavity (acoelom)
    • More advanced animals have a tube within a tube (pseudocoelom)
    • The most advanced animals have the inner tube suspended within the outer tube (coelom)

Phylum Porifera (Sponges)

  • Asymmetrical, sessile filter feeders with specialized cells:
    • Epidermal cells cover the outside of the sponge
    • Pore cells allow water to flow through the body wall
    • Choanocytes are flagellated cells that create water flow
    • Archaeocytes are amoeba-like cells that wander through the sponge and distribute nutrients and make spicules
  • Feeding, respiration, circulation, and excretion are all accomplished by water flow through the body wall and out the osculum
  • No nervous system, so minimal response to the environment
  • Can reproduce asexually or sexually

Phylum Cnidaria

  • Soft-bodied carnivores with radial symmetry, stinging tentacles, and only one opening (mouth/anus)
  • Have cnidocytes (stinging cells) with nematocysts (harpoon-like poison-filled structure)
  • Three layers:
    • Ectoderm (outer layer)
    • Mesoglea (jelly-like with neural network)
    • Gastroderm (where digestion takes place in gastrovascular cavity)
  • Two life stages:
    • Polyp: sessile with tentacles up
    • Medusa: motile with tentacles down

Feeding, Respiration, Circulation, and Excretion in Cnidarians

  • Catches prey with tentacles and pulls into the gastrovascular cavity
  • Digestion takes place and nutrients are absorbed through the gastroderm
  • Waste materials are released back out the mouth
  • All occurs by diffusion through the body wall
  • Loose association of nerves creates a neural network in mesoglea
  • Statocysts enable the cnidarian to detect gravity
  • Ocelli are light-detecting organs

Movement and Reproduction in Cnidarians

  • Circular and longitudinal muscles enable movement
  • Asexually: polyps can bud off new organisms
  • Sexually: separate medusa sexes release eggs and sperm into water (external fertilization)
  • Three classes of Cnidaria:
    • Scyphozoa (jellyfish)
    • Hydrozoa (branching polyp colonies, hydra, and Portuguese man-o-war)
    • Anthozoa (anemones and corals)

Phylum Platyhelminthes (Flatworms)

  • Soft-bodied, flattened worms with bilateral symmetry and cephalization
  • Flatworms can be free-living or parasitic
  • Feeding:
    • Free-living flatworms: carnivore scavengers that suck up material through a pharynx into a gastrovascular cavity
    • Parasitic flatworms: do not have a complex digestive system, rather just absorb nutrients through body by diffusion
  • Respiration, circulation, and excretion:
    • Bodies are thin and flat, relying on diffusion of materials through the body wall
    • Some free-living flatworms have flame cells that act to filter metabolic waste and remove it
  • Response:
    • Cephalized with an aggregation of neurons (ganglia) and sense organs
    • Two nerve cords run down the body
    • May have eyespots to detect light
    • Parasitic flatworms have a much simpler nervous system
  • Movement:
    • Free-living flatworms have cilia that allow them to glide through the water and muscles to wiggle
    • Parasitic flatworms are usually non-motile
  • Reproduction:
    • Asexual: fragmentation (fission) by splitting into 2 pieces
    • Sexual: most are hermaphrodites (male and female)
    • Parasitic: complex lifecycles with more than one host
  • Three classes of flatworms:
    • Turbellaria (free-living marine or freshwater)
    • Trematoda (Flukes, parasitic infecting internal organs of the host)
    • Cestoda (parasitic tapeworms infecting the digestive system of the host)

Phylum Nematoda (Roundworms)

  • Slender, unsegmented worms with a pseudocoelom
  • Feeding:
    • Most nematodes are free-living (carnivores or decomposers)
    • Some are internal parasites
  • Respiration, circulation, and excretion:
    • Due to small size, they rely on diffusion of gases and waste through their body wall
  • Response:
    • Simple nervous system consisting of several ganglia (groups of neurons), but no brain
  • Movement:
    • Longitudinal muscles as well as a pseudocoelom filled with fluid acts as a hydrostatic skeleton
    • Contraction of the muscles allows movement
  • Reproduction:
    • All sexual
    • Most have separate sexes
    • Internal fertilization
  • Many species of nematodes are human parasites, including Trichinosis Worms, Filarial Worms, and Ascarid Worms

Phylum Annelida

  • Segmented worms with a true coelom
  • Each segment has its own set of external appendages called setae
  • Feeding:
    • Can be carnivores, decomposers, or filter feeders
    • Pharynx has specialized feeding structures
    • Food moves through an esophagus, then a crop (storage), and a gizzard (grinding)
    • Nutrients are absorbed into each segment through the intestine
    • Waste is removed out the anus
  • Circulation:
    • Closed circulatory system (blood never leaves a vessel)
    • Blood moves toward head in the dorsal blood vessel
    • A set of 5 pairs of ring vessels act as hearts to pump blood
    • Ventral blood vessel carries blood towards rear of worm
  • Respiration:
    • Aquatic annelids have gills
    • Terrestrial annelids require moist skin to allow transport across it
  • Excretion:
    • Each segment has a pair of nephridia that remove waste
  • Response:
    • Cephalized (brain and sense organs at anterior)
    • Ventral nerve cord runs length of worm
  • Movement:
    • Hydrostatic skeleton
    • Setae evolve to aid movement
  • Reproduction:
    • Sexual (separate sexes and hermaphrodites)
    • External fertilization
  • Three classes of Annelids:
    • Oligochaetes (mostly terrestrial or freshwater, relatively small or reduced number of setae)
    • Polychaetes (mostly marine, many setae that have evolved into paddle-like structures)
    • Hirudinea (leeches, external parasites)

Phylum Mollusca

  • Soft-bodied animals with a free-swimming trochophore larvae stage
  • Four basic body parts:
    • Muscular foot: locomotion
    • Mantle: thin layer of tissue that covers body
    • Visceral mass: internal organs
    • Shell: may or may not be present
  • Feeding:
    • Snails have a rasp-like tongue called a radula to scrape
    • Octopi have a beak for ripping and tearing
    • Clams have a siphon that draws water in to be filtered
  • Respiration:
    • Aquatic molluscs have gills inside the mantle cavity
    • Terrestrial molluscs maintain a moist mantle to exchange gases
  • Circulation:
    • Snails and clams have an open system (blood flows through a few vessels and a heart, but also leaves a vessel and is free to slosh around the body cavity)
    • Octopi have a closed system as it is more efficient
  • Excretion:
    • Nephridia release waste outside body
  • Response:
    • Clams do not have a brain or complex nervous system
    • Snails have a simple brain and senses
    • Octopi have a well-developed brain and senses
  • Movement:
    • Clams dig with their foot
    • Snails glide on mucus and muscular contractions of the foot
    • Octopi have their foot divided into tentacles as well as can shoot water out of their siphon
  • Reproduction:
    • Many different strategies
    • Separate sexes or hermaphrodites

Understanding the characteristics of Kingdom Animalia, including eukaryotic, multicellular, heterotrophic, and lack of cell walls. Learn about the trends in animal evolution, such as cell specialization.

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