Invertebrates

• Porifera examples


  Sponges
• Cnidaria examples


  jellyfish and sea anemones
• when and from what did invertebrates evolve?

  Cambrian explosion from choanoflagellete-like organelles
• what are the earliest invertebrate fossils found?

  ediacaran biota
• describe the ediacaran biota

  quilted, leaf like, no internal organes but some had shells
• describe choanoflagellates


  single celled eukaryotes, flagellum for movement, actin collar for prey, can be colonial
• why are choanoflaggelates thought to be ancestor of animals?

  similar stucture to sponge choanocyte
• Sponge reproduction?

  HermaphroditismHermaphroditism

  -males broadcast spawn

  -asexual reproduction > regeneration
• porifera key features


  • no tissue layers
  • asymmetrical
  • Sessile
  • Filter feeder, carbon cycling
  • Broadcast spawning and internal fertilization, also regeneration
  • indirect development
• Ctenophora


  • comb jellies
  • radially symmetrical
  • Active swim- 8 cilia
  • Neural control (sensory organ)
  • Tentacles with toxic cells (sourced from jellyfish)
  • Protosome
  • Invasive
  • Simultaneous hermaphrodites- broadcast spawning or self-fertilisation (maybe fragmentation or regeneration)
  • Diploblastic
  • Direct development
• Cnidaria

  • corals, anemones, jellyfish etc
  • radially symmetrical
  • sessile and swimming phases
  • symbiotic photosynthetic microbes
  • colonial- zooids
  • polyps- sessile mouth upwards
  • medusae- mobile mouth downwards
  • blind gut
  • nerve network
  • sensory systems
  • cnidocytes are cells that contain nematocysts which release toxins
  • alternate between medusae (sexual) and polyp (asexual, regen) phases synchronised broadcast spawning
  • diploblastic
  • flurecent GFPs
• Lophotrochozoa


  • complete guts
  • Protosome blastopore

  contains many groups:

  • mollusc
  • Annelida
  • Ectoprocta
  • Platyhelminthes
• Mollusca


  • octopi, squid, clams, snails, slugs
  • flexible body plan (head-radula tooth, foot and visceral mass)
  • psuedocoelemic cavity has open circulation
  • Mantle cover visceral mass
  • Mantle cavity houses gills
  • Sexual reproduction, broadcast spawning, semelparity
  • Direct development in cephalopods and snails
  • Indirect development, ciliated trochophore larva
• three types of mollusc

  • bivalves (clams muscles)
  • filter feeders
  • foot burrows
  • gastropods (snails)
  • crawling grazing lifestyle
  • sensory tenacles
  • cephalopods (octopus, squids)
  • fast swimming predatory
  • shell internalised
  • beak, slicing radula, large brain
  • convergent evolution with human eyes
  • very intelligent
• Annelida


  • segmented worms
  • head, trunk, pygidium
  • Cephalised head
  • Trunk is further divided, some have appendages
  • Pygidium is the tail
  • Coelomic cavity is separated by septa
  • Each segment has its own hydrostatic skeleton
  • New segments can be added or modified
  • sexual reproduction is typical or epitokes (small adults filled with gametes) are produced
  • protosome
  • indirect via trochophore
  • sometimes direct development
• Vermicomposting


  Use of worms to produce compost
• Ectoprocta


  • small aquatic filter feeder (uses tentacular locophore)
  • Colonies of zooids
  • Exoskeleton
  • Reduced cephilisation
  • Bioconstructors
  • Hermaphroditic > broadcast spawning internal fertilization and brooding
  • Indirect development
• biofouling


  colonies growing on manmade things and causing damage
• Platyhelminthes


  • flatworms
  • triploblastic but lack a coelom (acoelmate)
  • two types
  • tubellarian
  • neodermata parasitic
  • monogeneans
  • trematodes (flukes)
  • cestodes (tapeworms)
• turbellarian (platyhelminths)


  • free-living
  • blind gut
  • lack circulatory and respiratory systems
  • coordinated waves of muscle action
  • asexual reproduction regeneration
  • sexual reproduction > widespread simultaneous hermaphrodites
  • penis fencing
  • dispersive cleavage early cells become unconnected then reunite and differentiate
  • direct and indirect
  • use toxins
• neodermata Platyhelminthes 


  Monogeneans- external parisite (direct single host species) non segmented

  Trematodes- internal parasite (indirect multiple hosts) non-segmented, complex halters (attachment structures)

  Cestodes (tapeworms)- internal parasite (indirect), pseudosegmented body plan, hermaphroditic egments (proglottids)
• ecdysozoan cuticle

  • body covering, exoskeleton
  • secreted proteins or polysaccarides
  • biomineralized or scleortized (proteins croslinked)
  • moulting (ecdysis)
  • periodically shed
  • energetic and ecological costs
  • leaves animal vulnerable
• Nematoda


  • roundworms
  • Cephalised
  • Pseudocoelomates with complete gut
  • Gas exchannge across cuticle
  • Pseudocoelom acts as a Hydrostatic skeleton
  • Longitudinal muscles
  • Most abundant animal group
  • Hermaphroditism (self-fertilization)
  • Cell consistency (eutely)
  • Alternative developmentsl pathways
  • Dauer stage- long term survival
  • Phenotypic plasticity
  • C.Elegans
  • Can parasitize anything
• C Elegans


  Deeply studied animal of all time

  • genomics
  • Senescence (genes regulating agin)
  • Molecular genetics
• anthropod


  Insect-lobster (jointed legs)
• Arthropod haplodiploidy


  Pominent in Hymenoptera (bees, wasps ants)

  • females borne of sexual reproduction have diploid genome
  • Males born of asexual parthenogenisis have haploid genome
  • Increased levels of relatedness between sisters
• arthopod development

  Requires moulting

  holometabolous- body plan change during pupal stage

  hemimetabolous- subtle changes with no pupal stage
• Echinodermata


  • sea stars, sea urchin and sea cucumbers
  • Radially symmetrical
  • Tube feet > water vascular system > locomotion and respiration
  • Complete gut mouth on bottom > stomach branches into legs
  • Most are motile some are sessile and attach
  • Sea Cucumber: bilateral, three rows of tube feet
  • Many different feeding styles- mostly benthic
  • Broadcast spawning- asexual reproduction
  • Indirect development