Annelida (segmented worms, leachs)

Annelida (segmented worms, leachs)

1. Leaches (Hirudinea)

   • Reproduction
     • Monoecious — cross-fertilize Internal fertilization – an ancestral character within Annelida Eggs deposited in a cocoon
     • Internal fertilization-ancestral traint in the annelida but usually not in other phylums Either semi-teresural, or aquadic
   • Feeding
     • Types of leaches will only go for certain prey
     • feeds, or preys, on the fluids
   • Sensory system
     • Thermoreceptors- can sense heat
   • Body pllan
     • Suckers for attachments (like in flat worms) Very muscular phyrax
       • the part of the alimentary canal immediately behind the mouth in invertebrates
     • Produce anti coagulant( thins your blood so they get a contain stream to drink)
     • Mimicry
       • some can look like leaves
   • THEY ARE NOT PARASITES
   • Predator Transitory relationship with their host NOT PARASITES They usually don’ kill
   • They can be used in medical proceeders to reduces pockets of liquid

2. Segmented worms/ polychaet

   • Body structure/
     • Bilateral symmetry
       • When you can split an animal in half into right and left sides that mirror each other.
     • Complete digestive tract and an anus
     • Have segmented parts, each segmented part is Metamerism-repeated sutures (multiple segments each having it’s own organ like a heart or something
       • Some metamerism in nervous system, circulatory system, osmoregulatory system, muscular system
       • Each segment has a Coelom cavity
         • Advantages to Metamerism: It means that the body is composed of repeating segments attached to make a whole.
           • Greater body length Better response to damage Regional specialization in body plan - tagmosis
       • Segments are separated from each other by mesodermal septa
     • Has ectoderm endoderm and mesoderm
       • Anatomical terminology. Ectoderm is one of the three primary germ layers in the very early embryo. The other two layers are the mesoderm (middle layer) and endoderm (most proximal layer), with the ectoderm as the most exterior (or distal) layer. It emerges and originates from the outer layer of germ cells.
   • Semi terrestrial- more moist environments
   • Reproduction
     • They have egg cases so that they stay moist
     • Hermaphrodites Each one delivers sperm each one given some
     • Some when they become older they add these segments called epitokys that are modified for either producing sperm or eggs, and they break off and release their sperm or eggs in the water.
   • Spiral, determinant cleavage
   • Nervous system
     • They have metameric segmentation(replication)- The repetition of organs and tissues at intervals along the body of an animal, thus dividing the body into a linear series of similar parts or segments
     • anterior ganglia (‘brain’) leads to ventral nerve cord nerve cord runs length of body with branchesin each segment
   • Circulatory system:(closed)
     • metameric closed anterior vessels muscularized and act as pumping “hearts” blood pumped from heart posteriorly in ventral vein, returns in dorsal vein each segment has branching vessel that loops from ventral to dorsal
       • Closed circulatory helps increase in movement
       • Each segement has a heart and blood vesals.
   • Excretion system:
     • Some osmoregulation occurs across body wall Most have paired metanephridia A ciliated funnel in coelom of one segment that leads to an exterior opening in adjacent segment
       • A metanephridium (meta = "after") is a type of excretory gland 
       • we see a simlar structure in flame cells (act like kindneys) in flat worms
   • Muscular system
     • metameric In each segment mesoderm has outer layer of circular muscle & inner layer of longitudinal muscle muscles act in opposition to fluid-filled coloem – a hydrostatic skeleton (seen in jelly fish as well
       •         Metameric A lott of muscles, longitudinal and circular can change the shape of the segments and help it’s movement     
   • Polychaet
     • Each Segment in polychaet has parapodia help it move
       • parapodia-each of a number of paired muscular bristle-bearing appendages used in locomotion, sensation, or respiration.
     • Move by means of paired appendages on each segment called parapodia – a defining characteristic Flap-like extensions of body wall supported by chitinous rods called setae Gas exchange through parapodia
       •        Move using their parapodia, which are like little fins on each segment (like a paddle )     
     • Fast swimmers 2 long antennae & agile parapodia propel them & catch zooplankton prey
     • Carnivarous feeders
     • They have Chemoreceptors to sense prey and potoceptors for light
     • Some polychaetes live in calcareous tubes, some in parchment tubes, some in tubes made out of sand grains
   • Digestion
     • Gut is a straight tube that runs the length of the body Mouth in an anterior segment: the prostomium Anus in a posterior segment: the pygidium
       • Alot of specilization
     • Mouth (may have muscularized, eversible pharynx)
       • Pharynx-the part of the alimentary canal immediately behind the mouth in invertebrates
     • Crop and gizzard- crunching and breaking up the food.
   • Lack parapodia - have spike-like setae instead
   • Feeding:
     • Terrestrial forms feed on vegetation / marine and fresh water types are deposit feeders
   • Other types
     • Some polychaetes are suspension feeders – let water flow passively Use mucous/cilia on radioles surrounding mouth to capture prey (These produce mucas and have cilia and can form nets tocapture, they are suspension feeders
     • Some polychates are filter feeders – actively pumping water Use mucous nets to capture prey
     • Blood warms (not a leach)- will suck the blood of fishes (some have tenticles
       • Can tolerate low oxygen conditions.