Chapter 12: Smaller Ecdysozoans

<<Protostomes<<

Ecdysozoans

  • Possess a cuticle
      * Nonliving external layer secreted by epidermis
      * If firm: restricts growth
        * Ecdysis required to grow
          * Molted

 Clade Panarthropoda with Phyla

<<Clade Panarthropoda<<

  • Phyla
      * Onychophora
      * Tardigrada
      * Arthropoda

  * All have a hemocoel
    * Fusion of main coelomic cavity and blastocoel
    * Blood from the open circulatory system enters
      * Surrounds internal organs
      * Blood + lymphatic fluid = hemolymph

<<Phylum Onychophora<<

  • Velvet worms
      * ~200 extant species
      * Found in rainforests, other tropical and semitropical leafy habitats
        * All terrestrial
        * Nocturnal
        * Require air saturated with moisture
      * Most are predators
        * Entangle and immobilize prey in slime
        * Prey digested by salivary enzymes
          * Velvet worms consume only liquid portion
  • Covered with soft cuticle
      * Contains chitin and protein and is molted in patches
  • Head
      * Pair of flexible antennae
        * Pigment-cup ocelli at the base (nearly blind)
  • 14-43 pairs of legs
      * Each ends with a flexible pad and two claws
  • Tracheal System
      * Enables them to breathe air
      * System of tubes that bring in air from pores scattered all over the body
  • Reproduction
      * Nearly all species are dioecious
      * In some species: viviparity
        * Placental attachment between mother and offspring
        * Live birth (offspring born as juveniles)
      * Other species: ovoviviparity
        * Young develop in eggs inside the mother
          * Hatch from eggs while in the uterus
          * Live birth
      * 2 Australian genera: oviparity
        * Females lay shell-covered eggs in moist places

<<Phylum Tardigrada<<

Video Notes

  • Eights legs
  • Not closely related to anything else on Earth
  • Clade Tactopoda
  • Found in three major aquatic environments: marine/brackish, freshwater, and films of water clinging to moss, etc.
  • Each tardigrade eye is a single photoreceptive cell
  • Covered in a cuticle (shed as tardigrade grows)
  • Have digestive systems, salivary glands, and even tiny brains
  • Life span from a few weeks to over 100 years
  • Cryptobyosis - metabolism lowers when conditions are bad, then replenishes, and roll into a tun to avoid being dried up
  • Anoxybiosis occurs when there is insufficient oxygen