Invertebrates 3 Nematoda and Annelida

Phylum Nematoda: The roundworms

Evolutionary relationships

Nematode body cavity: pseudocoelom  Mesoderm on inside of body wall, but not surrounding gut

Body plan  Feeding/digestive system  Nematodes suck!  Complete digestive system  Gas exchange  Body surface  Intestinal surface (minimal)  Body cavity (pseudocoelom)  No circulatory system  Excretory system/osmotic regulation  Exists, not well-understood  Locomotion:  Have only longitudinal muscles  Demo: The nematode swim!

Body plan (cont.)  Nervous system  “Brain”: nerve ring  Four nerve cords (where?)  Ganglia along ventral cord  Unique connection of muscles and nerves  Sensory structures

Reproduction, etc…  Reproduction  Sexes usually separate, but some hermaphrodites  Internal fertilization  Many parasitic forms  Trichina worms  Heartworms  River blindness  Elephantiasis  Also parasitic in plants

Phylum Annelida: The segmented worms

Evolutionary relationships

Aceolomates, Pseudocoelomates and Coelomates

PseudocoelomCoelom  Surface area for nutrient absorption and gas exchange ++ Larger organs ++ Fluid cushions/ protects organs ++ Hydrostatic skeleton is possible ++ Completely lined by mesoderm -+ Mesenteries suspend internal organs -+ Independent movement of gut -+

Basic Annelida features  Have all features of protostomes (know!)  Have body segmentation (new feature)  Repetition of body parts  Similar structures found in each region  Some specialization of regions  Some continuous parts (digestive system)

Annelid diversity Class Polychaeta Class Oligochaeta Class Hirudinea

Body Plan (earthworm)  Digestive system  Complete  Specialized regions  Circulation  Closed system  Multiple hearts  Gas exchange  Body surface  Coelom  Parapodia (Polychaetes)  Excretory  Metanephridia

Body Plan (cont.)  Nervous system  Brain (=cerebral ganglia)  Ventral nerve cord (fused pair of cords)  One ganglion per segment  Movement  Peristalsis  Setae

Feeding in different classes  Class Oligochaeta: Earthworms   Earth suckers (create vacuum by expanding muscular pharnyx)   Why important in ecosystem?  Class Polychaeta: Marine segmented worms   Many are tentacle feeders   Many other feeding modes  Class Hirudinea: Leeches   Food suckers (create vacuum by expanding pharynx, digestive tract)   How do blood sucking leeches feed?.   What three substances do blood sucking leeches secrete to aid in the process?   NOTE: Not all leeches are blood suckers!