CoelomatesProtostomes

• Mouth develops from the blastopore

• Cleavage is spiral and determinate

• ALL HAVE A TRUE COELOM!

Mollusca• Bilateral symmetry• Open circulatory system• Soft bodied, with hard shell protection• Reduced or no segmentation• Radula; rasping tongue to sxrape food• True coelom• Many internal organs• Three body parts

– Foot– Visceral mass– Mantle

Four Classes• Polyplacophora

– Chitons– Cling to rocks– Live on rocky shores– Use muscular foot to grip

• Gastropods– Snails, slugs, nudibranchs– Largest class– Shell protects body– Torsion leads to twisted body– Uses radula to scrape algae and graze on

plants

• Bivalves:– Clams, oysters, mussels, scallops– Possess shell divided and hinged into two halves– Filter feeders– Sedentary lifestyle

• Cephalopods– Squid and octopus and nautilus– Use jaws to bite prey– Mouth as base of foot (foot drawn into several

tentacles)– Complex brains and capable of learning and

moving fast– Mantle reduced or absent– Can get large, How?

Annelids• SEGMENTATION!• Closed circulatory system• Alimentary canal• Five pairs of hearts• Gas exchange across skin• Metanephridia for gas exchange• Nitrogenous wastes exit from each segment

through pores• Nervous system with ganglia and ventral

nerve cords

Three classes:• Oligocheates

– Earthworms

• Polycheates:– Fanworms– Tube dwellers (marine)

• Hirudinea:– Leaches– Used to treat bruised tissues and to stimulate

circulation

Evolutionary trends in Annelids

• Coelom – serves as hydrostatic skeleton– Developed complex organ system– Protects internal structures

• Segmentation– Specialization of body segments

Arthropods

• Key characteristics:– Jointed appendages– Segmentation– Hard exoskeletons– Extensive cephalization– Open circulatory system– Gas exchange gills in water, book lungs or spiracles

on land

Success vs. Limitations

• Successes:– Exoskeleton, lets the thrive on land, but

limited– Jointed appendages allowed for walking

and then flying in some– More successful organization of segments

• Limits:– Exoskeleton is shed– Limited brain size– Limited body size

Subphyla• Trilobites

– Extinct group– Show pronounced segmentation, with little

variation in appendages– Early, primitive arthropods

• Chelicerates– Includes the arachnids– 1-2 body segments with 8 legs

• Uniramia– Includes insects, milipedes and centipedes

Classes

• Arachnids– Scorpions, spiders, mites

• Insects– 1pair of antennae– 6 legs– 3 body segments

• Crustaceans– Crabs, crayfish, lobsters, isopods (pill bugs)– 2 or 3 body segments

Deuterostomes

• Radial indeterminate cleavage

• Blastopore becomes the anus

Echinoderms

• Secondarily evolved radial symmetry

• Unique water vascular system

• Has mouth and anus

• Has endoskeleton

Classes

• Aseroidea– Sea stars

• Ophiuroidea– Brittle stars

• Echinoidea– Sea urchins and sand dollars

• Holothuroidea– Sea cucumbers

To what phylum does this organism belong?

Phylum Annelida

To what phylum does this organism belong?

Phylum Cnidaria

To what phylum does this organism belong?

Phylum Mollusca

To what phylum does this organism belong?

Phylum Echinodermata

To what phylum does this organism belong?

Phylum Arthropoda

To what phylum does this organism belong?

Phylum Nematoda

To what phylum does this organism belong?

Phylum Platyhelminthes

To what phylum does this organism belong?

Phylum Porifera

What evolutionary innovation both led to and limited the success of the

phylum to which this organism belongs?

. . . the exoskeleton

What type of symmetry does this organism exhibit?

. . . none

What evolutionary innovation does the phylum to which this organism

belongs have over Nematoda?

. . . segmentation

What is unique about the digestive system of this organism, and others

that belong to the same phylum?

. . . it is one way; having both a mouth and an anus

What two evolutionary innovations are common to the phylum to which

this organism belongs?

. . . bilateral symmetry and celphalization

What type of symmetry does this organism, and others belonging to

the same phylum, exhibit?

. . . radial symmetry

What evolutionary innovation is first exhibited by the phylum to which this

organism (a giant squid) belongs?

. . . the coelom

                   

                         

                                                                             

                                                                                                     

                                      

                                      

An open circulatory

system limits the size of these

animals

The closed circulatory system is

much more efficient!