Animals: The Invertebrates Chapter 23

Characteristics of Animals Multicelled heterotrophic eukaryotes that ingest or parasitize other organisms. Require oxygen for aerobic respiration Reproduce sexually, and perhaps asexually Motile at some stage Develop from embryos Almost all have tissues, organs and organ systems. Animals originate during late precambrian.

Major Animal Phyla

Symmetry Radial Bilateral

The Gut Region where food is digested and then absorbed Saclike gut –One opening for taking in food and expelling waste Complete digestive system –Opening at both ends; mouth and anus

Body Cavities - Acoelomate epidermis gut cavity no body cavity; region between gut and body wall packed with organs

Body Cavities - Pseudocoel epidermis gut cavity unlined body cavity (pseudocoel) around gut

Body Cavities - Coelom gut cavity peritoneum lined body cavity (coelom)

Segmentation Repeating series of body units Units may or may not be similar to one another Earthworms - segments appear similar Insects - segments may be fused and/or have specialized functions

Animal Origins Originated during the Precambrian (1.2 billion million years ago) From what? Two hypotheses: –Multinucleated ciliate became compartmentalized –Cells in a colonial flagellate became specialized

Phylum Placozoa One living species, Tricoplax adherens Simplest known animal Two-layer body, 3 mm across

Sponges - Phylum Porifera No symmetry No tissues No organs Reproduce sexually Microscopic swimming-larval stage

Sponge Structure central cavity water out water in flagellummicrovillinucleus glasslike structural elements amoeboid cell pore semifluid matrix flattened surface cells

Phylum Cnidaria Only animals that produce nematocysts Nerve net Hydrostatic skeleton Saclike gut

Cnidarian Diversity Scyphozoans –Jellyfish Anthozoans –Sea anemones –Corals Hydrozoans

Two Main Body Plans outer epithelium (epidermis) mesoglea (matrix) inner epithelium (gastrodermis) polyp medusa

Obelia Life Cycle (Hydrozoan) reproductive polyp female medusa male medusa sperm zygote ovum planula polyp forming feeding polyp

Flatworms: Phylum Platyhelminthes Acoelomate, bilateral, cephalized animals All have simple or complex organ systems Most are hermaphrodites

Three Classes Turbellarians (Turbellaria) Flukes (Trematoda) Tapeworms (Cestoda)

Planarian Organ Systems brainnerve cord genital pore oviduct testis ovary penis

Planarian Organ Systems pharynx protonephridia flame cell nucleus cilia fluid filters through membrane folds flame cell opening of tubule at body surface

Flukes: Class Trematoda Parasitic worms Complicated life cycle –Larval stage infects a mollusk –Adult infects a vertebrate Cilated larva Worms mate in human host Fertilized egg Asexual reproduction in intermediate host Larvae form, leave snail Larvae bore into human skin Southeast Asian blood fluke

Tapeworms: Class Cestoda Larvae encysted in muscle tissue Intermediate host Mature proglottid with fertilized eggs Scolex attaches to host intestinal wall Definitive host

Roundworms (Nematoda) False coelom Complete digestive system gonadpharynxintestine false coelom eggs in uterusanus muscularized body wall

Two Coelomate Lineages Protostomes Mollusks Annelids Arthropods Deuterostomes Echinoderms Chordates

Cleavage Patterns Protostome embryo (spiral cleavage) Deuterostome embryo (radial cleavage)

First Opening in Embryo coelom pouch will form mesoderm around coelom solid mass of mesoderm developing gut protostome deuterostome

Bilateral, soft-bodied coelomate Most have a shell or reduced version of one Mantle drapes over body and secretes shell Most have a fleshy foot Many have a radula for shredding food Mollusks: Phylum Mollusca

Gastropods Chitons Bivalves Cephalopods Molluscan Diversity

Twisting of body parts during larval development Occurs only in gastropods Before torsion: head faces forward and anus faces backward After torsion: anus is positioned over head Torsion

Body Plan of a Snail mouth anus gill anus radula foot mantle cavity digestive gland mantle heart

Body Plan of a Clam mouth retractor muscle left mantle retractor muscle foot palps left gill shell

Cephalopods Only the nautilus retains external shell Other cephalopods are streamlined, active swimmers All move by jet propulsion –Water is forced out of mantle cavity through a funnel-shaped siphon Have large brains relative to body size

Cuttlefish Body Plan Closed circulatory system with heart and accessory heart anus siphon gill heart accessory heart shell brain reproductive organ stomach digestive gland radula

Segmented, coelomate worms Class Polychaeta Class Oligochaeta Class Hirudinea Annelids: Phylum Annelida

Polychaetes Most are marine Bristles extend from paired, fleshy parapods on each segment Head end is specialized

Predators and parasites Less obvious body segmentation Most have sharp jaws Leeches - Class Hirudinea

No parapodia, few bristles per segment Earthworm - An Oligochaete Nerve cord Dorsal blood vessel Nephridium Coelom Circular muscle Longitudinal muscle Seta (retracted)

Earthworm Circulatory System Hearts

Earthworm Digestive System Pharynx Esophagus Crop Gizzard Coelomic chambers Mouth

Earthworm Nervous System Brain Nerve cord

The phylum with the greatest number of species Four lineages: –Trilobites (all extinct) –Chelicerates (spiders, mites, scorpions) –Crustaceans (crabs, shrimps, barnacles) –Uniramians (insects, centipedes, millipedes) Arthropods: Phylum Arthropoda

Adaptations for Success Hardened exoskeleton Jointed appendages Fused and modified segments Respiratory structures Specialized sensory structures Division of labor

Originated in seas A few are still marine: horseshoe crabs, sea spiders The arachnids are all terrestrial Spiders Mites Scorpions Chiggers “Daddy longlegs” Ticks Chelicerates

Body Plan of a Spider chelicera heart pedipalp book lung brain Malpighian tubule anus silk gland

Most are marine, some freshwater, a few terrestrial Head has two pairs of antenna, three pairs of food-handling appendages Crustaceans Copepods Crayfish Barnacles Lobsters Shrimps Crabs Isopods (pillbugs)

Lobster Body Plan antennae (two pairs) one of two eyes fused segments of cephalothorax segments of abdomen tail fin swimmerets five walking legs (five pairs total) first leg food-handling appendages (three pairs)

Crab Life Cycle Larval and juvenile stages molt repeatedly and grow in size

Millipedes and Centipedes Segmented bodies with many legs Millipedes –Two pairs of legs per “segment” –Scavengers Centipedes –Flattened with one pairs of legs per segment –Predators

Insect Body Plan Thorax usually has three pairs of legs and one or two pairs of wings Abdomen contains most internal organs and specialized structure for reproduction Three-part gut Malpighian tubules attach to midgut and serve in elimination of wastes

Insect Headparts antenna labrum palps maxilla labium mandible Grasshopper Butterfly Fly Mosquito

Insect Diversity Insects are the only winged invertebrates There are more than 800,000 known species Most successful species are small in size and have a great reproductive capacity

adult youngegg nymphsegg larvaeegg Growth and molting Incomplete metamorphosis Complete metamorphosis Types of Insect Development

Echinoderms Deuterostomes Almost all are marine Body wall has spines or plates of calcium carbonate No brain Adults are radial with bilateral features

Echinoderm Diversity Crinoids (sea lilies and feather stars) Sea stars Brittle stars Sea urchins, heart urchins, sand dollars Sea cucumbers

Body Plan of a Sea Star eyespot digestive gland gonad anus lower stomach upper stomach coelom sieve plate

Water Vascular System sieve plate ampulla