Invertebrates 3 Phylum Annelida and Phylum Mollusca

Branchpoints: Pseudocoelomate vs. coelomate Protostomes vs. deuterostomes

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? -+

Protostomes vs. deuterostomes Fig 32.7

Major Protostome Phyla (traditional phylogeny)  Phylum Annelida  Phylum Mollusca  Phylum Arthropoda

Phylum Annelida: The segmented worms

Basic Annelida features  Have all features of coelomates and 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)

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

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

Annelid diversity  Earthworms  Marine segmented worms  Leeches See previous diagrams

Feeding in different classes  Earthworms  Earth suckers (create vacuum by expanding muscular pharnyx); lots left undigested  Process 40 tons of soil/acre of earth/year!  improve aeration/drainage  Leeches  Create vacuum by expanding pharynx, digestive tract  Blood suckers hang on with suckers, feed with jaws or have pharynx they stick into prey, suck out blood.  Secrete anticoagulants, vasodilators and numbing agents  Marine segmented worms  Wide variety of feeding modes

Phylum Mollusca: The “soft-bodied” animals

Evolutionary relationships  Protostomes, same branch as annelids.

Molluscan body plan (HAM)  Shell  Mantle  Visceral mass  Mantle cavity  With ctenidia  Head and assocated sensory structures  Radula  Foot and epipodial tentacles

Molluscan body plan (HAM)  Digestive system  complete  note position of anus  Circulation/Respiration  ctenidium  open circulatory system  coelom=pericardial cavity.  True coelom, but reduced.  Water/ion balance and ammonia excretion  Has paired nephridia: kidney-like in function

Molluscan body plan (HAM)  Nervous system  few ganglia at key locations, connected by paired ventral nerve cords.  have brain  several sensory structures (see description of HAM)

Major Molluscan Classes  LEARN!: How is HAM modified for each of the major classes? ?

Class Polyplacophora: “many plates”  The chitons  Differences from HAM  8 shell plates  Expanded mantle cav.  Multiple ctenidia  Mantle grows over shell  Reduced head

Class Gastropoda: “stomach-foot”  Representative members: Snails, limpets, abalone, nudibranchs, sea and land slugs  Differences from HAM  Undergo torsion (sketch)  What is torsion  Advantages of torsion  Disadvantages of torsion

Class Bivalvia: “two valves”  Representative members: Clams, mussels and scallops  Differences from HAM  Two shells  Expanded mantle cavity  Enlarged ctenidia  Respiration AND feeding  Reduced head  Foot more elongate

Class Cephalopoda: “Head-footed”  Representative members: Nautilus, squid, octopus  Differences from HAM  Shell reduced (pen in squid)  Foot gives rise to  tentacles  funnel  Mantle  Thickened and protective  Functions in movement  Nervous system highly developed  Great brain!  Eyes similar to vertebrates  Circulatory system closed!  Other features