Lesson 9: Non Arthropod Ecdysozoans

Ecdysozoa

• “to strip off” → moult

• 8 subphylum 

  • nematoda

  • nematomorpha 

  • lorichifera

  • kinorhyncha 

  • priapulida 

  • onychophora 

  • tardigrada

  • arthropoda 

Nematoda

• roundworms 

• very abundant all over the world, very high human impact 

  • most important of all parasitic animal groups

  • ecto and endo parasitic

• reproduction results in 100, 000s of eggs

Nematoda structure 

• adapted mouth parks 

• thick cuticle made of collagen 

• fluid-filled pseudocoelom functions as a hydrostatic skeleton 

• no circular muscles 

Common nematoda parasites

• intestinal roundworms 

  • ~1 billion people infected

• hookworms 

  • ~650 million people infected

• pinworms 

  • dont need an intermediate host

  • most common nematode parasite of developed countries

• filarial worms 

  • arthropod transmission

  • ~200 million people infected

Caenorhabditis elegans

• free-living, non hazardous, non parasitic, non infectious nematode 

• one of the most important experimental biological models 

  • all 959 cells traced from zygote to adult 

  • entire nervous system known 

  • genome entirely mapped 

Nematomorpha 

• horsehair worms 

• pseudocoelomate 

• semi-parasitic 

  • adults are free living

  • juveniles are parasitic in arthropods

• pathenogenetic reproduction

  • a form of asexual reproduction in which a new organism develops from an unfertilized egg, without a male's contribution

    

Panarthropoda

• subsection of ecdysozoa which includes: 

  • onychophora 

  • tardigrade

  • arthropods 

• small coelom

• ventrolateral appendages: walking pairs 

• homocoel and open circulatory system 

  • blood + lymph = hemolymph 

Onychophora

• velvet worms

  • soft “velvelt-like” cuticle

  • repels water

• 14-43 pairs of unjointed legs with pad and 2 claws

Tardigrada

• water bears

• 8 unjointed legs with claws

• pair of sharp stylets and sucking pharynx 

  • used to pierce and suck plant juices/small invertebrates 

• parthenogenetic or sexual reproduction

• cryptobiosis= tun state

  • a reversible state where an organism's metabolism temporarily ceases to survive extreme environmental conditions like freezing, desiccation, or oxygen deficiency

Nematoda organization

• organ system

Nematoda symmetry

• bilateral

Nematoda body cavity

• pseudocoelomate

Nematoda development

Nematoda segmentation

• no