textbook 102 arthropods

textbook 102 arthropods

1. most diverse phylum

   • most abundant number of animals

2. very evolutionarily successful

   • the complex and flexible 'body plan' features, make arthropods evolutionarily successful!!
     • 1. exoskeleton
       • 2. segmentation
         • 3. presence of a coelem
           • 4. cephalization
             • 5. bilateral symmetry
               • 6. jointed limbs
                 • These six characteristics all together makes them different from other invertebrates!
                   • all these characteristics makes them evolutionarily successful
                     • Annelids are restricted to aquatic or moist environments!
                       • arthropods are not restricted to aquatic or moist environments
                         • other phylum are restricted by their body plans, in ways arthropods are not
                           • 1. echnioderms: have a coelem and strong exoskeleton, but have radial symmetry and lack of cephalization limit mobility
             • key nervous tissues/ brain, as well as sensory organs and appendages are at the head/front
           • in multicellular animals, membrane between wall of gut and body wall, contains internal organs
           • annelids have this too
         • internal and external segmentation
         • annelids have this too
       • annelids dont have, protects against fluid loss
     • the body plan contributing to the ecological flexibility and evolutionary diversification
       • 1. segmented bodies
         • each segment has a pair of jointed, flexible appendages
         • segmentation is key! allows for
           • repetition of functional elements
             • diversity of function among those differentiated segments
         • segmentation allows for TAGMOSIS
           • TAGMOSIS: process- blocks of segments grouped together, become specialised for a particular function
             • (like tissue cells in organisms)
             • 1 segment: tagma
               • groups of segments: tagmatas
                 • insect body plans are three tagmatas
                   • 1. head
                     • 2. abdomen
                       • 3. thorax
                       • have groups of specialised appendages for different functions eg paddling
                         • these groups can evolve independently of eachother, so allowing for ecological flexibility, different niches
                           • appendages are jointed for rapid movement, off the substrate, don't have to slither like other invertebrates
                             • arthropod limb structures are either 2 types
                               • 1.biramous
                                 • 2. uniramous
                                   • unbranched like legs of an insect
                                     • consists of multiple jointed segments, allows flexible movement
                                 • appendage that forks in to two branches, each of which can have independent function
                     • cephalization: sensory organs and nervous tissue at front

3. more than ONE MILLION species of arthropods!!

   • four fifths of all known species!!

4. many are undescribed!! 5-10 million or up to 30 million species!!

5. origins 530 million years ago, with marine species fossil records

   • earliest common ancestor has: strong exoskeleton, pair of limbs, modular segmentation
     • the earliest fossils of land animals are arthropods !
       • diversified into many different ecological niches
         • including mites, spiders, butterflies, spiders, beetles