Chapter 33

Lack a backbone 95% of known animal species Occupy almost every habitat on Earth

No True tissues No symmetry Suspension feeders Most are hermaphroditic

Radial symmetry All have cnidocytes Diploblastic Gastrovascular cavity (no anus) Carnivorous Body plan: Polyp Medusa Simple muscle system Simple nerve net nervous system, no brain

Hydrozoa Alternate polyp and medusa in life cycle, with polyp as dominant stage Alternate polyp and medusa in life cycle, with polyp as dominant stage Examples: colonial hydroids, hydra, Portuguese Man of War Examples: colonial hydroids, hydra, Portuguese Man of War Scyphozoa: Prominent medusa Examples jellyfish Anthozoa: Polyps are dominant Sea anemonies, and coral

Lack coelom Bilateral symmetry What evolutionary novelty comes with bilateral symmetry? Cephalization

What new novelties are seen in this phylum? Triploblastic, so has muscular system Organs Cephalization, more complex nervous system

Turbellaria: Carnivorous Moves by cilia Eyespots on head Rudimentary brain Diffusion for gas exchange Excretion through flame cells Hermaphroditic

Often called flukes All members are parasitic What makes a parasite in good standing? Become an egg machine since it is hard to find a host Use intermediate hosts Develop hooks and suckers Hermaphroditism, so that limits need to find others

Tapeworms Parasitic Scolex in adult hooks onto the host intestines Proglottids for reproduction Eggs eaten by intermediate host and larva develops Final host infected by eating intermediate host encysted with larva forms Do not eat poorly cooked meats!

Not quite a true coelom, missing the inner lining of muscle

Mostly marine 1 st to get an anus Organs lie in the pseudocoelom Parthogenesis – unfertilized eggs develop into females

Many found in soil, useful for nutrient recycling Complete digestive tract Some are parasitic, e.g. trichinella and hookworm (dogs)

Mouth develops from the blastopore Cleavage is radial and determinate ALL HAVE A TRUE COELOM!

Bilateral symmetry Open circulatory system Soft bodied, with hard shell protection Most have exoskeletons Reduced or no segmentation Radula; rasping tongue to scrape food True coelom Many internal organs Three body parts Foot Visceral mass Mantle

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 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?

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

Oligocheates Earthworms Polycheates: Fanworms Tube dwellers (marine) Hirudinea: Leeches Used to treat bruised tissues and to stimulate circulation Used to treat bruised tissues and to stimulate circulation

Coelom Serves as hydrostatic skeleton Developed complex organ system Protects internal structures Segmentation Specialization of body segments

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

Successes: Exoskeleton, lets them 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

Trilobites Extinct group Show pronounced segmentation, with little variation in appendages 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, millipedes and centipedes

Arachnids Scorpions, spiders, mites Insects 1 pair of antennae 6 legs 3 body segments Crustaceans Crabs, crayfish, lobsters, isopods (pill bugs) 2 or 3 body segments

Radial indeterminate cleavage Blastopore becomes the anus

Secondarily evolved radial symmetry Unique water vascular system Has mouth and anus Has endoskeleton

Aseroidea Sea stars Ophiuroidea Brittle stars Echinoidea Sea urchins and sand dollars Holothuroidea Sea cucumbers

Phylum Annelida

Phylum Cnidaria

Phylum Mollusca

Phylum Echinodermata

Phylum Arthropoda

Phylum Nematoda

Phylum Platyhelminthes

Phylum Porifera

... the exoskeleton

... none

... segmentation

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

... bilateral symmetry and cephalization

... radial symmetry

... the coelom

An open circulatory system limits the size of these animals

The closed circulatory system is much more efficient!