Animal Evolution The Invertebrates

Animal Evolution The Invertebrates

More than 500 predatory mollusks live in the sea Use conotoxins to paralyze their prey Conotoxins interest biologists as potential sources for new drugs

C. geographicus secretes a toxin that one day might help epileptics The gene that codes for the enzyme gammaglutamyl carboxylase (GGC) catalyzes a step in the conotoxin synthesis pathway

GGC is present in insects and humans, but functions in blood clotting in our bodies GGC gene must have been around for at least the past 500 million years in a common ancestor

Multicelled heterotrophic eukaryotes Require oxygen for aerobic respiration Reproduce sexually, and perhaps asexually Motile at some stage Develop from embryos

Fig. 25-2a, p.404

Fig. 25-2c, p.405

Chordate s Echinoderms Arthropods Annelids CoelomateAncestry Mollusks Rotifers Bilateral Ancestry Roundworms Flatworms Multicelled Ancestry Radial Ancestry Cnidarians Sponges Single-celled, protistanlike ancestors

Ectoderm Endoderm Epithelium

Originated during the Precambrian (1.2 billion - 670 million years ago) From what? Two hypotheses: Multinucleated ciliate became compartmentalized Cells in a colonial flagellate became specialized

Animal Origins Fig. 25-4b, p.405

Symmetry Fig. 25-5, p.406

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

epidermis gut cavity no body cavity; region between gut and body wall packed with organs Fig. 25-6, p.406

epidermis gut cavity unlined body cavity (pseudocoel) around gut Fig. 25-6, p.406

gut cavity lined body cavity (coelom) peritoneum Fig. 25-6, p.406

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

Segmentation sponges cnidarians flatworms annelids mollusks roundworms arthropods echinoderms chordates coelom lost coelom reduced pseudocoel coelom reduced molting radial ancestry, two germ layers PROTOSTOMES mouth from blastopore DEUTEROSOMES anus from blastopore multicelled body true tissues bilateral, coelomate ancestry, three germ layers Fig. 25-7, p.407

One living species, Tricoplax adherens Simplest known animal Two-layer body, 3 mm across Fig. 25-11, p.409

No symmetry No tissues No organs Reproduce sexually Microscopic swimming larval stage

water out glasslike structural elements central cavity amoeboid cell pore semifluid matrix flattene d surface cells water in flagellum microvilli nucleus Stepped Art Fig. 25-10, p.409

Fig. 25-9c, p.408

Fig. 25-9d, p.408

Only animals that produce nematocysts Nerve net Hydrostatic skeleton Saclike gut capsule s lid at free surface of epidermal cell trigger barbed thread inside capsule nematocyst Fig. 25-13, p.410

Scyphozoans Jellyfish Anthozoans Sea anemones Corals Hydrozoans

outer epithelium (epidermis) Polyp mesoglea (matrix) Medusa inner epithelium (gastrodermis) Fig. 25-12, p.410

Fig. 25-14a2, p.411

Fig. 25-14b, p.411

Acoelomate, bilateral, cephalized animals All have simple or complex organ systems Most are hermaphrodites

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

Fig. 25-16, p.412

proglottids scolex a Larvae, each with inverted scolex of future tapeworm, become encysted in intermediate host tissues (e.g., skeletal muscle) b A human, a definitive host, eats infected, undercooked beef which is mainly skeletal muscle d Inside each fertilized egg, an embryonic, larval form develops. Cattle may ingest embryonated eggs or ripe proglottids, and so become intermediate hosts c Each sexually mature proglottid has female and male organs. Ripe proglottids containing fertilized eggs leave host in feces, which may contaminate water and vegetation. Fig. 25-18, p.413

proglottids scolex Fig. 25-18e, p.413

Segmented, coelomate worms Class Polychaeta Class Oligochaeta Class Hirudinea

jaws Most are marine Bristles extend from paired, fleshy parapods on each segment Head end is specialized toothlike structures pharynx (everted ) antenna palp (food handling) tentacle eyes chemicalsensing pit parapod

Predators and parasites Less obvious body segmentation Most have sharp jaws

before feeding Fig. 25-20a, p.414

No parapodia, few bristles per segment Dorsal blood vessel Circular muscle Longitudinal muscle Nerve cord Coelom Nephridium Nerve cord Seta (retracted) Fig. 25-21, p.415

bladderlike storage region of nephridium nephridium s thin loop reabsorbs some solutes, relinquishes them to blood blood vessels body wall funnel (coelomic fluid external pore (fluid containing with waste enters here) wastes discharged here) Fig. 25-21, p.415

Hearts Fig. 25-21, p.415

Coelomic chambers Pharynx Esophagus Crop Gizzard Mouth Fig. 25-21, p.415

Brain Nerve cord Fig. 25-21, p.415

head end Fig. 25-21g, p.415

Bilateral Cephalized False coelom Crown of cilia at head end Complete gut

Protostomes Deuterostomes Mollusks Annelids Arthropods Echinoderms Chordates

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

pouch will form mesoderm around coelom protostome developing gut coelom solid mass of mesoderm deuterostome developing gut

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

Gastropods Chitins Bivalves Cephalopods

Twisting of body parts during larval development Occurs only in gastropods mouth gill anus Fig. 25-23a, p.416

mantle cavity heart anus gill mantle digestive gland foot radula Fig. 25-23, p.416

mouth left mantle retractor muscle retractor muscle foot palps left gill shell Figure 25.25 Page 417

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

Fig. 25-26c, p.418

False coelom Complete digestive system pharynx intestine eggs in uterus gonad anus false coelom muscularized body wall Fig. 25-27, p.419

Fig. 25-28a, p.419

Fig. 25-28c, p.419

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

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)

Hardened exoskeleton Jointed appendages Fused and modified segments Respiratory structures Specialized sensory structures Division of labor Figure 25.29 Page 420

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

Chelicerates Fig. 25-30a, p.421

Chelicerates Fig. 25-30b, p.421

eye brain hear t digestive gland Malpighian tubule poison gland pedipalp chelicera mouth book lung sperm receptacle ovary silk gland spinners anus Fig. 25-30, p.421

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

antennae (two pairs) one of two eyes fused segments of cephalothorax segments of abdomen food-handling appendages (three pairs) first leg swimmerets tail fin five walking legs (five pairs total) Fig. 25-32, p.422

Segmented bodies with many legs Millipedes Two pairs of legs per segment Scavengers Centipedes Flattened, with one pair of legs per segment Predators

Fig. 25-34a, p.423

Fig. 25-34b, p.423

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

The only winged invertebrates More than 800,000 known species Most successful species are small in size and have a great reproductive capacity

Fig. 25-37a, p.425

Fig. 25-37c, p.425

Fig. 25-37g, p.425

Poisonous spiders Disease-carrying ticks Venomous scorpions Agricultural pests Corn rootworm (Diabrotica virgifera) Fig. 25-41, p.427

Harmful Spiders Fig. 25-38b, p.426

Fig. 25-39b, p.426

Bark Scorpion Fig. 25-40, p.427

Mosquito Fig. 25-42, p.427

Deuterostomes Body wall has spines or plates No brain Adults are radial with bilateral features Sea urchin Sea cucumber Brittle star

Fig. 25-43, p.428

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

Fig. 25-44a, p.429

Body plan of a sea star

sieve plate ampulla Figure 25.44f Page 429