C8 Part 1

• Learning Objectives


  • Explain about animal's origin
  • List out animal's general characteristics
  • Describe the phyla of invertebrates, by explaining and differentiating their characteristics besides discussing their life cycle
• Origins of animals


  Many biologists agree that animals evolve from protists (protistan) about 900 million years ago
• Hypothesized lineages that animals may originate from

  • Choanoflagellates
  • Ciliates
  • Spherical Colonies
  • Placozoans

  
• Choanoflagellates


  A group of protists that are suspension feeder and possess collar cells
• Ciliates


  Unicellular ciliates - Paramecium that possess two types of nucleus
• Colonies


  Spherical colonies - Volvox colony that becomes mutated
• Placozoan


  The placozoan Trichoplax adhaerens that is a plate-shaped, two layered animal with no symmetry and no organs
• General characteristics of animals

  • Multicellular eukaryotes with tissues arranged in organs and organ systems
  • Heterotrophic - obtaining carbon compound and energy by ingesting other animals/by absorbing nutrients from them
  • Require oxygen for aerobic respiration
  • Reproduce sexually and in some cases asexually or both
  • Most are motile during at least part of their life
  • Life cycles include a period of embryonic development
• Variations in animal body plans

  • Existence of Backbone
  • Body Symmetry and Cephalization
  • Type of guts
  • Body Tissues
  • Coelom
  • Segmentation
• Vertebrates


  Animals with backbones
• Invertebrates


  Animals without backbones
• Radial symmetry


  Body parts arranged regularly around a central axis
• Radial animals live in water because their body plan is adapted to receive food drifting/swimming towards them from any direction
• Bilateral symmetry


  Body axis passing from an anterior end (front) to a posterior end (back), with right and left sides along this main axis, and a dorsal surface (backside) and ventral surface (underside)
• Cephalization


  Concentration of the nervous system and feeding features at the head end
• Saclike gut


  One opening only, the mouth, where food is digested and absorbed into the internal environment
• Tubular gut


  A "complete" digestive tract, with two openings (mouth and anus) for continuous food processing, often through specialized regions
• Tripoblastic


  Possessing three germ layers: ectoderm, mesoderm, and endoderm
• Coelom


  Fluid-filled space in between the gut and the body wall of most bilateral animals
• Coelomate


  Animals with a coelom lined with peritoneum
• Pseudocoelom


  A "false" coelom not lined with peritoneum, with direct contact with the wall of the digestive tract
• Acoelomate


  Animals without a coelom, with tissues filling the region between the gut and body wall
• Segmentation


  Composed of repeating body units that may or may not be similar to one another
• Sponges (Phylum Porifera) are different from other animals because they have an asymmetric body, lack true tissues and organs
• Sponges are mostly marine animals, of widely varying size and shape, while only a few are freshwater species
• Pores (ostia)


  Hundreds of tiny pores in sponges, through which water enters and flows out
• Cell types in sponges

  • Flattened pinacocyte cells
  • Tubelike porocyte cells
  • Collar cells (choanocyte)
  • Amoeboid amoebocyte cells
• Suspension feeding


  Sponges filter a large amount of water for food, trapping suspended particles in the collars of choanocyte cells
• Mesohyl


  Semifluid matrix between the two cell layers, containing skeletal spicules
• Reasons for sponge survival

  • Most predators dislike their taste due to the spicules
  • Most sponges are smelly
• Sexual reproduction in sponges

  1. Sperm released into water, picked up by nearby sponge and directed to egg

  2. Zygote develops into free-swimming flagellated larva that attaches and settles
• Asexual reproduction in sponges

  1. Fragmentation - small fragments break off and grow

  2. Gemmule formation - clusters of spore-like cells that can survive harsh conditions
• Cnidarians are diploblastic, possessing only two germ layers (ectoderm and endoderm)
• Cnidarians have diversified into a wide range of both sessile and motile forms including jellies, corals, and hydras
• Most cnidarians live in the seas, only a few species live in freshwater
• Radial symmetry


  The symmetry possessed by adult cnidarians
• Nematocyst


  The unique stinging devices possessed by cnidarians
• Fragmentation


  Small fragments break away from the parent and grow into new sponges
• Gemmules


  Clusters of spore-like collection of sponge cells that can survive until living conditions improve
• Phylum Cnidaria


  • Diploblastic, where they possess only two germ layers/tissue layers
  • Body lack the mesoderm layer
  • Diversified into a wide range of both sessile and motile forms including jellies, corals, and hydras
  • Most cnidarians live in the seas; only a few species live in freshwater