invertebrates

• After this lecture you should be able to...
• Invertebrates


  • Account for 95% of known animal species
  • Incredibly diverse

  
• Deuterostomia


  The most ancient branch point in the animal phylogeny results in two lineages having: radial or bilateral symmetry, a well-defined head or no head, diploblastic or triploblastic embryos, true tissues or no tissues

  
• Porifera


  • Sponges
  • Basal animals
  • Lack true tissues
  • Asymmetrical
  • Sedentary
  • Live in marine or freshwater
  • Suspension feeders

  
• Ctenophora


  • Comb jellies
  • Radial symmetry
  • Diploblastic
  • Debate on their phylogeny
  • Basal eumetazoans

  
• Cnidaria


  • Jellyfish, anemones, corals and hydras
  • Corals have a symbiotic relationship with dinoflagellates
  • Radial symmetry
  • Diploblastic
  • Sessile and motile forms
  • Body plan is sac with central digestive compartment
  • Single opening as mouth and anus
  • Nerve net

  
• Cnidocytes


  Stinging cells
• Cnidarians are the sister taxa to bilaterians
• The majority of animals are Bilaterians
• Three large clades of Bilaterians


  • Lophotrochozoa
  • Ecdysozoa
  • Deuterostomia
• Acoela is the basal bilaterian clade
• Bilaterians


  • Bilateral symmetry
  • Triploblastic development
  • True coelom
  • Digestive tract with two openings
  • Central nervous system
• Lophotrochozoa


  • Platyhelminthes (flatworms)
  • Syndermata (previously Rotifera; rotifers)
  • Mollusca (molluscs)
  • Annelida (annelids)
• Platyhelminthes


  • Flatworms
  • Bilateral symmetry
  • Acoelomate
  • Aquatic and damp terrestrial habitats
  • Gastrovascular cavity with single opening
  • Some are parasitic (Trematodes, Tapeworms, Flukes)

  
• Platyhelminthes


  • Planarian
  • Fuchsia flatworm
  • Tapeworm
• Syndermata


  • Rotifers
  • Live in aquatic and damp terrestrial habitats
  • Pseudocoelomate
  • Digestive tube with separate mouth and anus
  • Can reproduce asexually by parthenogenesis (females produce offspring from unfertilized eggs)
• Mollusca


  • Gastropods, bivalves, and cephalopods
  • Most are marine
  • Ceolemate
  • Open and closed circulatory systems
  • Soft-bodied animals, some protected by a hard shell
  • Intelligence in cephalopods

  
• Mollusca


  • Clam
  • Cuttlefish
• Annelida


  • 2 main groups: Polychaetes (bristle worms) and Oligochaetes (earthworms and leeches)
  • Bodies composed of fused rings
  • Coelomate
  • Closed circulatory system
• Annelida


  • Leech
  • Bristleworm
  • Earthworm
• Ecdysozoans: most species-rich animal group

  
• Ecdysis


  Shedding of cuticle
• Cuticle


  Tough outer coat (exoskeleton) providing support and protection
• Nematoda


  • Roundworms
  • Parasitic, live in body fluids and tissues of animals
  • Reproduce sexually, by internal fertilization
  • Examples: Trichinella spp., C. elegans (a model organism)
• Arthropoda


  • Segmented body plan
  • Hard exoskeleton (cuticle)
  • Open circulatory system
  • Specialized jointed appendages (walking, feeding, sensory reception, reproduction, defense)
• 3 major subphyla of Arthropods


  • Chelicerata: horseshoe crabs, scorpions, ticks, mites and spiders
  • Myriapoda: centipedes and millipedes
  • Pancrustacea: Crustaceans (crabs, lobsters, shrimps and barnacles) and Hexapods (insects and relatives; greatest number of species)

  
• Deuterostomia


  Shared developmental characteristics: radial, indeterminate cleavage, formation of the anus from the blastopore
• Echinoderms


  • Sea stars, sea urchins, sand dollars, brittle stars, & sea cucumbers
  • Slow-moving or sessile marine animals
  • Water-vascular system and hydrostatic skeleton
  • External sexual reproduction

  
• Chordates


  • 4 defining characteristics: notochord, dorsal, hollow nerve cord, pharyngeal slits, post-anal tail