Mollusks and Annelids Chapter 23+ 1
Annelids and Mollusks Coelomates Trochophore larvae Bilateral symmetry More complex organ systems 2
Moving On Up 3
Coelom Coelomates Evolutionary milestone True body cavity Forms within mesoderm Internal body organs cushioned by fluids in cavity 4
Trochophore Larva Larval stage Most Mollusks and Annelids Suggests related? Develops from fertilized egg Ciliated In some species free-swimming 5
The Mollusks Second largest animal phylum Widespread More species of terrestrial mollusks than all terrestrial vertebrates 7 classes 6
Mollusk Characteristics Body cavity True coelom Small area around heart Bilateral symmetry Three part body plan Foot Muscular Locomotion Visceral mass Contains organs Mantle Fold of tissue Outer layer of body Cape-like 7
Characteristics- Continued More organ systems Excretion, circulation, respiration, digestion, and reproduction Shell Many mollusks One or two Protein + CaCO 3 Protection Radula All, except bivalves Tongue-like Rasping Feeding 8
Mollusk Classification Domain = Eukarya Kingdom = Animalia Phylum = Molluska Three major classes: Gastropoda Bivalvia Cephalopoda Nemo Mollusk joke 1:15 9
Mollusks Only coelomates w/out segmented body 10
Mollusk Digestion Complete digestive system One-way Two openings Varies in mollusk groups More complex than roundworms 11
Mollusk Excretion Removal of metabolic wastes Wastes in body fluids collect in coelom Fluid pulled into nephridia by cilia Tiny tubes Recover water, sugars, and salts 12
Excretion Useful molecules reabsorbed Waste fluid leaves through pore in mantle cavity All coelomates have nephridia except Arthropods Chordates 13
Mollusk Circulation Circulatory system! Diffusion won t work Most: 3 chambered heart Open system Blood sloshes in hemocoel Exception: Octopi and squid 14
Mollusk Respiration Most have gills: In mantle cavity Cilia beat and move water Gills extract >50% of dissolved O 2 15
Mollusk Respiration Terrestrial snails Membrane lines mantle cavity Primitive lung Must be moist Active at night and after rain Sea snails No gills Gas exchange thru skin 16
Mollusk Reproduction Most = distinct sexes Some snails and slugs are hermaphrodites Some sea slugs and oysters can change back and forth between sexes! 17
Reproduction Larval forms Many marine mollusks have trochophore Ciliated and moves Squid, octopi, and freshwater snails and some freshwater mussels No free swimming larva Larva form within egg 18
Just to really keep your interest! Celtic Mollusk presentation 3:30 19
Gastropods 20
Gastropods Largest mollusk class 40,000 species Snails, nudibranches, and slugs Single or no shell 21
Gastropoda Muscular foot - locomotion Mostly marine Size Microscopic to 1 meter Nudibranch clip - 27 sec Nudibranchs California Academy of Sciences (Low) 4 min.mp4 22
Gastropod Feeding Habits Some herbivores Radula Scrape algae off rocks Some are predators Radula Drill into other mollusks Ex: Cone shell Uses poison Swallow prey 23
Gastropods and Humans Can be pests Garden and agricultural Can be eaten Genus Helix raised on snail farms Conchs are considered delicacies 24
Bivalvia 25
Bivalves All aquatic Most marine Two hinged shells Secreted by mantle Ligaments and muscles hold shells together Adductor muscles 26
Bivalves Head is reduced Radula absent Most are filter feeders Most are sessile 27
Bivalve Nervous System Nerve ganglion Simple brain Simple sense organs Sense organs on edge of mantle Sensitive to light and touch Giant Clam 6:47 28
Bivalve Reproductive System Most have distinct sexes Few hermaphrodites Reproduce sexually Release gametes into water 29
Bivalve Reproductive System Fertilized egg develops into free swimming trochophore larva Few brooded in pouches Then complete life cycle as parasite on fish gills 30
Bivalve Filter Feeding Slow moving creatures Cilia on gills Create water flow Siphons Hollow tubes Inlet and outlet Gills Mucus covered Trap microorganisms Cilia move mucus to mouth 31
Bivalve and Humans Human food resource Oysters, clams, scallops, mussels Over 6.5 billion lbs/yr Demand increasing 32
Bivalve and Pearls Many bivalves produce pearls: Foreign object trapped between shell and mantle Coat irritant with sheets of nacre Mother-of pearl Like the inner layer of shell 33
Bivalve and Pearls Only a few species Gem-quality pearls Pearls Thin sheets of nacre Over-lapping mineral crystals Act-like prisms Makes pearls iridescent Cultured pearls 34
Clam Structure 35
Clam Structure 36
Cephalopods 37
Cephalopods Shell is reduced or absent Nautilus is the only living cephalopod with an external shell Small internal shell of cuttlefish Bird cages for calcium Active marine predators Closed circulatory system Beak-like jaws Large head Foot divided into tentacles Suckers or hooks 38
Shark vs Octopus showdown 39
Cephalopods Most advanced group of mollusks Most intelligent of all invertebrates Complex nervous system Well developed brain Eye structure similar to vertebrate eye Exhibit complex behaviors Cephalopod character 3:40 40
Cephalopod Movement Jet propelled Draw water into mantle cavity When threatened Close mantle cavity quickly Force water out of siphon 41
Cephalopod Escape Squids and octopuses Release dark fluid Clouds water Confuses predators Conceals escape route Cuttlefish ink Sepia Used by artists Many famous paintings Cephalopod Defense 2:30 42
Cephalopod Feeding Marine predators Eat Fish Crustaceans Worms Use: Tentacles Beak-like jaws Radula pulls in food Feeding video 2 min 43
Moving On Up 44
The Segmented Worms Phylum annelida Anellus Latin - Little rings Segmented bodies Also known as metamerism All coelomate animals except mollusks Evolutionary milestone 45
Body Segments Series of ring-like structures Each segment contains organs: Digestive, excretory, circulatory, muscular Some segments modified Special function: Reproduction, feeding, sensation Septa Internal body walls that separate segments 46
General Characteristics 1) Coelom Larger than mollusks 2) Most have bristles Setae - external bristles Parapodia - fleshy appendages 3) Organ Systems Highly specialized Closed circulatory system Nephridia Digestive system Primitive brain = cerebral ganglion 47
Annelid Classification Domain Eukarya Kingdom Animalia Phylum Annelida Classes: 1) Polychaeta 2) Oligochaeta 3) Hirudinea Differ in # of setae/segment Presence/absence of parapodia 48
Class Polychaeta Poly = many Chaeta = seta Marine worms Largest group of annelids Live in all oceans Often have setae Feather duster worm 49
Class Polychaeta Unusual forms and colors Pair of parapodia on most segments Swim, crawl, burrow Increase surface area Gas exchange 50
Class Polychaeta Tube worms Form Protective tubes Secretions and sand Ex: Feather duster Filterfeeder 51
Class Polychaeta Nereis Predataor Free swimming 52
Class Oligochaeta Oligo = few Chaeta = seta Earthworms & freshwater worms No parapodia Few setae/segment Size varies mm to 3 meters 53
Earthworms Lack distinct head region Specialized scavengers Eat their weight in soil each day Thousands of earthworms per acre No eyes Have light sensitive organs Hydrostatic skeleton 54
Earthworm Humor 55
Earthworm Gas Exchange No respiratory system Gas exchange through its skin Diffuses into blood capillaries Skin must be moist Covered in a watery mucus 56
Earthworm Digestive System Complete digestive tract One way street Mouth Pharynx Esophagus Crop Thin walled storage chamber Gizzard Muscular grinding chamber Intestine Anus Castings 57
Earthworm Circulatory System Closed circulatory system Blood stays in vessels Dorsal blood vessel Aortic arches (hearts) Ventral blood vessel 58
Earthworm Nervous System Primitive brain Cerebral ganglion Ventral nerve cord Segmental nerves 59
Earthworm Reproduction All hermaphrodites Two worms mate Each exchanges sperm Clitellum Enlarged band-like structure Secretes the cocoon (w/ fertilized eggs) Deposited in soil 60
Internal Structure 61
Internal Structure 62
Ventral Surface 63
Earthworm Basic Structure 64
Cross-Section of Earthworm 65
Cross-Section of Earthworm 66
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Review Anatomy 68
Dissection Overview 69
Earthworm Dissection Pharynx Esophagus Crop Gizzard Intestine Dorsal BV Septa Mouth 70
Earthworm Dissection 71
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Class Hirudinea Leeches No setae No parapodia Flattened bodies Segments not separated internally Most predators or scavengers Some are parasites 73
Class Hirudinea (Leeches) Suckers on both ends Used in medical field Medicinal Leaches 2:00 74