Chapter 28 Invertebrates

• Invertebrates


  • Lack a backbone
  • Account for more than 95% of known animal species
  • Morphologically diverse and occupy almost every habitat on Earth
• Invertebrates are animals that lack a backbone
• Animal phyla

  • Porifera
  • Ctenophora
  • Cnidaria
  • Acoela
  • Platyhelminthes
  • Syndermata
  • Ectoprocta
  • Brachiopoda
  • Hemichordata
  • Echinodermata
  • Chordata
  • Mollusca
  • Annelida
  • Nematoda
  • Arthropoda
• Eumetazoa


  Clade of animals with tissues
• Bilateria


  Clade of animals with bilateral symmetry, including most invertebrates except chordates
• Protostomes


  One of the three major clades of bilaterian animals
• Deuterostomes


  One of the three major clades of bilaterian animals, including chordates
• Lophotrochozoa


  One of the three major clades of bilaterian animals
• Ecdysozoa


  One of the three major clades of bilaterian animals
• Porifera (Sponges)


  • Aquatic, mostly marine
  • Sessile as adults
  • No nervous, digestive, respiratory, circulatory, or reproductive system
  • Filter feeders
  • No true tissue or cephalization
• Spongocytes, lophocytes, collenocytes, sclerocytes

  Sponge cell types

  
• Porifera (Sponges)


  • Body supported by hard spicules and protein fibers (spongin)
  • Reproduce asexually by fragmentation or budding, and sexually as hermaphrodites

  
• Cnidaria


  • Radial symmetry
  • Aquatic, in two adult body forms: sessile polyp and drifting/free-swimming medusa
  • No cephalization
  • Sac-like body with gastrovascular cavity and single opening (mouth/anus)
  • Mesoglea as non-cellular hydrostatic skeleton
  • Simple nervous system with non-centralized nerve net
• Cnidocytes


  Specialized cells that house stinging structures (nematocysts)
• Lophotrochozoans


  • Some develop a lophophore for feeding, others pass through a trochophore larval stage, and a few have neither feature
• Platyhelminthes (Flatworms)


  • Live in marine, freshwater, and damp terrestrial habitats
  • Many are parasites like flukes and tapeworms
  • Acoelomates with a gastrovascular cavity and one opening
  • Flat shape increases surface area for gas exchange and waste elimination by diffusion

  
• Platyhelminthes (Flatworms)


  • Have cephalization, a centralized nervous system with ganglia and nerve cords, and eyespots
  • Excretory system with protonephridia and flame cells

  
• Platyhelminthes (Tapeworms)


  • Parasitic, mostly in vertebrate intestines
  • Lack a mouth or gastrovascular cavity, instead absorbing nutrients directly from the host's intestine
• Syndermata (Rotifers)


  • Free-living, aquatic
  • Microscopic, cylindrical body
  • Crown of cilia draws a vortex of water into the mouth
  • Jaws grind up food (microorganisms)
  • Pseudocoelom
  • Alimentary canal with mouth and anus
  • Parthenogenesis (asexual reproduction)
• Ectoprocts, Brachiopods


  • Have a crown of ciliated tentacles (lophophore) around their mouth used for feeding
• Mollusca (Molluscs)


  • Soft-bodied, often protected by a calcium carbonate shell
  • Most are marine, some inhabit freshwater or are terrestrial
  • Have true coeloms and complex organ systems
  • Cephalization present except in bivalves
  • Digestive system with a strap-like radula for feeding
• Molluscan body plan


  Muscular foot, visceral mass, and mantle
• Mollusca (Molluscs)


  • Have specialized gas exchange surfaces like gills or simple lungs
  • Most have open circulatory systems
  • Most have separate sexes and trochophore larvae
• Annelida (Segmented Worms)


  • Have segmentation (metamerism) with repeated external and internal features
  • Soft body with true coelom acting as hydrostatic skeleton
  • Well-developed organ systems including digestive, circulatory, excretory, and nervous systems
  • Gas exchange occurs across the moist body surface

  
• Errantia


  Mobile marine predatory annelids with fleshy parapodia and sensory cirri

  
• Sedentaria


  Less mobile annelids with elaborate tentacles
• Chitin


  Polysaccharide that makes up the exoskeleton of arthropods
• Make up


  1. Molluscs

  2. Pearl

  3. Animal group with largest number of species

  4. Extinction
• Lophotrochozoans: Annelida - segmented worms


  • Segmentation (metamerism) of external and internal features
  • Soft body with true coelom as hydrostatic skeleton
  • Well-developed organ systems - digestive, closed circulatory, excretory, nervous
  • Gas exchange across moist body surface

  
• Anatomy of an earthworm

  Benefits: allows animals to become bigger, their movement is more efficient
• Clusters of nerve cells are a type of primitive body
• Kidney


  Respiratory system is not well developed
• Recent molecular analyses indicate that the annelids can be divided into two major clades: Errantia and Sedentaria
• Errantia


  • Most mobile marine predators
  • Fleshy parapodia for locomotion and gas exchange
  • Detects prey with long sensory organs called cirri
• Sedentaria


  • Less mobile
  • Elaborate tentacles used for filter feeding and gas exchange
• Types of annelids


  • Earthworms with few bristles and no parapodia
  • Terrestrial or freshwater deposit-feeders that aerate soils
  • Leeches with no bristles and no parapodia, most live in fresh water, some are terrestrial, have anti-coagulant (hirudin)
• Sedentarians ingest soil particles (detritus)
• Leeches don't let blood clot so they can drink more
• Phyla


  • Platyhelminthes (flatworms)
  • Syndermata (rotifers and acanthocephalans)
  • Lophophorates (Ectoprocta, Brachiopoda)
  • Mollusca (clams, snails, squids)
  • Annelida (segmented worms)

  
• Ecdysozoans


  • Most species-rich animal group
  • Covered by a tough coat called a cuticle
  • Cuticle is shed or molted through a process called ecdysis
  • Two largest phyla are nematodes and arthropods