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LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson Chapter 33 An Introduction to Invertebrates Lectures by Erin Barley Kathleen Fitzpatrick © 2011 Pearson Education, Inc. Overview: Life Without a Backbone • Invertebrates are animals that lack a backbone • They account for 95% of known animal species • They are morphologically diverse – For example, the Christmas tree worm (Spirobranchus giganteus) has tentacles for gas exchange and feeding © 2011 Pearson Education, Inc. Figure 33.1 Figure 33.2 Porifera ANCESTRAL PROTIST Lophotrochozoa Bilateria Eumetazoa Common ancestor of all animals Cnidaria Ecdysozoa Deuterostomia Figure 33.3a Porifera (5,500 species) Placozoa (1 species) 0.5 mm A sponge Cnidaria (10,000 species) A placozoan (LM) Ctenophora (100 species) A jelly Acoela (400 species) 1.5 mm Acoel flatworms (LM) A ctenophore, or comb jelly Figure 33.3aa A sponge Figure 33.3ab A jelly Figure 33.3ac 1.5 mm Acoel flatworms (LM) Figure 33.3ad 0.5 mm A placozoan (LM) Figure 33.3ae A ctenophore, or comb jelly Figure 33.3b Platyhelminthes (20,000 species) Rotifera (1,800 species) 0.1 mm Ectoprocta (4,500 species) Ectoprocts A marine flatworm Acanthocephala (1,100 species) Nemertea (900 species) Brachiopoda (335 species) A brachiopod A rotifer (LM) Annelida (16,500 species) Cycliophora (1 species) Curved hooks 100 m An acanthocephalan (LM) Mollusca (93,000 species) A ribbon worm An octopus A cycliophoran (colorized SEM) Lophotrochozoa A marine annelid Figure 33.3ba A marine flatworm Figure 33.3bb Ectoprocts 0.1 mm Figure 33.3bc A rotifer (LM) Figure 33.3bd A brachiopod Figure 33.3be Curved hooks An acanthocephalan (LM) Figure 33.3bf A ribbon worm Figure 33.3bg 100 m A cycliophoran (colorized SEM) Figure 33.3bh A marine annelid Figure 33.3bi An octopus Figure 33.3c Loricifera (10 species) Priapula (16 species) Onychophora (110 species) 50 m A loriciferan (LM) A priapulan An onychophoran Nematoda (25,000 species) Tardigrada (800 species) Arthropoda (1,000,000 species) 100 m A roundworm (colored SEM) Ecdysozoa Tardigrades (colorized SEM) A scorpion (an arachnid) Figure 33.3ca 50 m A loriciferan (LM) Figure 33.3cb A priapulan Figure 33.3cc An onychophoran Figure 33.3cd A roundworm (colored SEM) Figure 33.3ce 100 m Tardigrades (colorized SEM) Figure 33.3cf A scorpion (an arachnid) Figure 33.3d Hemichordata (85 species) Chordata (52,000 species) A tunicate Echinodermata (7,000 species) An acorn worm Deuterostomia A sea urchin Figure 33.3da An acorn worm Figure 33.3db A tunicate Figure 33.3dc A sea urchin Concept 33.1: Sponges are basal animals that lack true tissues • Animals in the phylum Porifera are known informally as sponges • They are sedentary and live in marine waters or fresh water © 2011 Pearson Education, Inc. Figure 33.UN01 Porifera Cnidaria Lophotrochozoa Ecdysozoa Deuterostomia • Sponges are suspension feeders, capturing food particles suspended in the water that passes through their body • Water is drawn through pores into a cavity called the spongocoel and out through an opening called the osculum • Sponges lack true tissues and organs © 2011 Pearson Education, Inc. Figure 33.4 Azure vase sponge (Callyspongia plicifera) Food particles in mucus Flagellum Choanocyte Collar Choanocyte Osculum Phagocytosis of food particles Amoebocyte Spongocoel Pore Spicules Epidermis Mesohyl Water flow Amoebocytes Figure 33.4a Azure vase sponge (Callyspongia plicifera) Figure 33.4b Choanocyte Osculum Spongocoel Pore Spicules Epidermis Mesohyl Water flow Amoebocytes Figure 33.4c Food particles in mucus Flagellum Choanocyte Collar Phagocytosis of food particles Amoebocyte • Choanocytes, flagellated collar cells, generate a water current through the sponge and ingest suspended food • Sponges consist of a gelatinous noncellular mesohyl layer between two cell layers • Amoebocytes are found in the mesohyl and play roles in digestion and structure • Most sponges are hermaphrodites: Each individual functions as both male and female © 2011 Pearson Education, Inc. Concept 33.2: Cnidarians are an ancient phylum of eumetazoans • All animals except sponges and a few other groups belong to the clade Eumetazoa, animals with true tissues • Phylum Cnidaria is one of the oldest groups in this clade © 2011 Pearson Education, Inc. Figure 33.UN02 Eumetazoa Porifera Cnidaria Lophotrochozoa Ecdysozoa Deuterostomia • Cnidarians have diversified into a wide range of both sessile and motile forms including jellies, corals, and hydras • They exhibit a relatively simple diploblastic, radial body plan • The basic body plan of a cnidarian is a sac with a central digestive compartment, the gastrovascular cavity • A single opening functions as mouth and anus © 2011 Pearson Education, Inc. • There are two variations on the body plan: the sessile polyp and motile medusa • A polyp adheres to the substrate by the aboral end of its body • A medusa has a bell-shaped body with its mouth on the underside • Medusae do not attach to the substate but move freely © 2011 Pearson Education, Inc. Figure 33.5 Mouth/anus Tentacle Gastrovascular cavity Gastrodermis Mesoglea Body stalk Epidermis Tentacle Polyp Mouth/anus Medusa • Cnidarians are carnivores that use tentacles to capture prey • The tentacles are armed with cnidocytes, unique cells that function in defense and capture of prey • Nematocysts are specialized organelles within cnidocytes that eject a stinging thread © 2011 Pearson Education, Inc. Figure 33.6 Tentacle Cuticle of prey Thread Nematocyst “Trigger” Thread discharges Cnidocyte Thread (coiled) • Phylum Cnidaria is divided into four major classes – – – – Hydrozoa Scyphozoa Cubozoa Anthozoa © 2011 Pearson Education, Inc. Figure 33.7 (b) Scyphozoa (a) Hydrozoa (c) Cubozoa (d) Anthozoa Figure 33.7a (a) Hydrozoa Figure 33.7b (b) Scyphozoa Figure 33.7c (c) Cubozoa Figure 33.7d (d) Anthozoa Hydrozoans • Most hydrozoans alternate between polyp and medusa forms • Hydra, a freshwater cnidarian, exists only in polyp form and reproduces asexually by budding © 2011 Pearson Education, Inc. Figure 33.8-1 Feeding polyp Reproductive polyp Medusa bud Gonad Medusa 1 mm Portion of a colony of polyps Key Haploid (n) Diploid (2n) Figure 33.8-2 Feeding polyp Reproductive polyp Medusa bud MEIOSIS Gonad Medusa Egg Sperm SEXUAL REPRODUCTION 1 mm Portion of a colony of polyps FERTILIZATION Zygote Key Haploid (n) Diploid (2n) Figure 33.8-3 Feeding polyp Reproductive polyp Medusa bud MEIOSIS Gonad Medusa Egg ASEXUAL REPRODUCTION (BUDDING) Portion of a colony of polyps SEXUAL REPRODUCTION FERTILIZATION Developing polyp 1 mm Sperm Mature polyp Zygote Planula (larva) Key Haploid (n) Diploid (2n) 1 mm Figure 33.8a Scyphozoans • In the class Scyphozoa, jellies (medusae) are the prevalent form of the life cycle © 2011 Pearson Education, Inc. Cubozoans • In the class Cubozoa, which includes box jellies and sea wasps, the medusa is box-shaped and has complex eyes • Cubozoans often have highly toxic cnidocytes © 2011 Pearson Education, Inc. Anthozoans • Class Anthozoa includes the corals and sea anemones, and these cnidarians occur only as polyps • Corals often form symbioses with algae and secrete a hard external skeleton © 2011 Pearson Education, Inc. Concept 33.3: Lophotrochozoans, a clade identified by molecular data, have the widest range of animal body forms • Bilaterian animals have bilateral symmetry and triploblastic development • Most have a coelom and a digestive tract with two openings • The clade Bilateria contains Lophotrochozoa, Ecdysozoa, and Deuterostomia © 2011 Pearson Education, Inc. Figure 33.UN03 Bilateria Porifera Cnidaria Lophotrochozoa Ecdysozoa Deuterostomia • The clade Lophotrochozoa was identified by molecular data • Some develop a lophophore for feeding, others pass through a trochophore larval stage, and a few have neither feature • Lophotrochozoa includes the flatworms, rotifers, ectoprocts, brachiopods, molluscs, and annelids © 2011 Pearson Education, Inc. Flatworms • Members of phylum Platyhelminthes live in marine, freshwater, and damp terrestrial habitats • Although flatworms undergo triploblastic development, they are acoelomates • They are flattened dorsoventrally and have a gastrovascular cavity with one opening • Gas exchange takes place across the surface, and protonephridia regulate the osmotic balance © 2011 Pearson Education, Inc. • Flatworms are divided into two lineages – Catenulida, or “chain worms,” reproduce asexually by budding – Rhabditophora are more diverse and include both free-living and parasitic species © 2011 Pearson Education, Inc. Figure 33.9 5 mm Free-Living Species • The best-known rhabditophorans are planarians • Planarians live in fresh water and prey on smaller animals • Planarians have light-sensitive eyespots and centralized nerve nets © 2011 Pearson Education, Inc. • The planarian nervous system is more complex and centralized than the nerve nets of cnidarians • Planarians are hermaphrodites and can reproduce sexually, or asexually through fission © 2011 Pearson Education, Inc. Figure 33.10 Gastrovascular cavity Pharynx Gastrovascular cavity Mouth Eyespots Ventral nerve cords Ganglia Parasitic Species • Parasitic rhabditophorans live in or on other animals • Two important groups of parasitic rhabditophorans are the trematodes and the tapeworms © 2011 Pearson Education, Inc. Trematodes • Trematodes parasitize a wide range of hosts, and most have complex life cycles with alternating sexual and asexual stages • Trematodes that parasitize humans spend part of their lives in snail hosts • They produce surface proteins that mimic their host and release molecules that manipulate the host’s immune system © 2011 Pearson Education, Inc. Figure 33.11 Male Human host Female 1 mm Mature flukes Ciliated larva Motile larva Snail host Figure 33.11a Male Female 1 mm Mature flukes Tapeworms • Tapeworms are parasites of vertebrates and lack a digestive system • Tapeworms absorb nutrients from the host’s intestine © 2011 Pearson Education, Inc. • The scolex contains suckers and hooks for attaching to the host • Proglottids are units that contain sex organs and form a ribbon behind the scolex • Fertilized eggs, produced by sexual reproduction, leave the host’s body in feces © 2011 Pearson Education, Inc. Figure 33.12 100 m Hooks Sucker Proglottids with reproductive structures Scolex Figure 33.12a 100 m Hooks Sucker Rotifers • Rotifers, phylum Rotifera, are tiny animals that inhabit fresh water, the ocean, and damp soil • Rotifers are smaller than many protists but are truly multicellular and have specialized organ systems © 2011 Pearson Education, Inc. Figure 33.13 Jaws Anus Stomach Crown of cilia 0.1 mm • Rotifers have an alimentary canal, a digestive tube with a separate mouth and anus that lies within a fluid-filled pseudocoelom • Rotifers reproduce by parthenogenesis, in which females produce offspring from unfertilized eggs • Some species are unusual in that they lack males entirely © 2011 Pearson Education, Inc. Lophophorates: Ectoprocts and Brachiopods • Lophophorates have a lophophore, a crown of ciliated tentacles around their mouth • Lophophorates have a true coelom • Lophophorates include two phyla: Ectoprocta and Brachiopoda © 2011 Pearson Education, Inc. • Ectoprocts (also called bryozoans) are sessile colonial animals that superficially resemble plants • A hard exoskeleton encases the colony, and some species are reef builders © 2011 Pearson Education, Inc. Figure 33.14 Lophophore (a) Ectoprocts, colonial lophophorates Lophophore (b) Lampshell, a brachiopod Figure 33.14a Lophophore (a) Ectoprocts, colonial lophophorates • Brachiopods superficially resemble clams and other hinge-shelled molluscs, but the two halves of the shell are dorsal and ventral rather than lateral as in clams • Brachiopods are marine and attach to the seafloor by a stalk © 2011 Pearson Education, Inc. Figure 33.14b Lophophore (b) Lampshell, a brachiopod Molluscs • Phylum Mollusca includes snails and slugs, oysters and clams, and octopuses and squids • Most molluscs are marine, though some inhabit fresh water and some snails and slugs are terrestrial • Molluscs are soft-bodied animals, but most are protected by a hard shell © 2011 Pearson Education, Inc. • All molluscs have a similar body plan with three main parts – Muscular foot – Visceral mass – Mantle • Many molluscs also have a water-filled mantle cavity and feed using a rasplike radula © 2011 Pearson Education, Inc. Figure 33.15 Nephridium Heart Visceral mass Coelom Digestive tract Intestine Gonads Mantle Stomach Shell Radula Mantle cavity Mouth Anus Gill Foot Nerve cords Esophagus Mouth Radula • Most molluscs have separate sexes with gonads located in the visceral mass, but many snails are hermaphrodites • The life cycle of many molluscs includes a ciliated larval stage called a trochophore © 2011 Pearson Education, Inc. • Four of the major classes of molluscs are – – – – Polyplacophora (chitons) Gastropoda (snails and slugs) Bivalvia (clams, oysters, and other bivalves) Cephalopoda (squids, octopuses, cuttlefish, and chambered nautiluses) © 2011 Pearson Education, Inc. Chitons • Chitons are oval-shaped marine animals encased in an armor of eight dorsal plates • They use their foot like a suction cup to grip rock, and their radula to scrape algae off the rock surface © 2011 Pearson Education, Inc. Figure 33.16 Gastropods • About three-quarters of all living species of molluscs are gastropods © 2011 Pearson Education, Inc. Figure 33.17 (a) A land snail (b) A sea slug (nudibranch) Figure 33.17a (a) A land snail Figure 33.17b (b) A sea slug (nudibranch) • Most gastropods are marine, but many are freshwater and terrestrial species • The most distinctive characteristic of gastropods is torsion, which causes the animal’s anus and mantle to end up above its head; torsion is different from the coiling of a shell • Most have a single, spiraled shell • Slugs lack a shell or have a reduced shell © 2011 Pearson Education, Inc. Figure 33.18 Mantle cavity Anus Mouth Stomach Intestine Bivalves • Bivalves are marine and include many species of clams, oysters, mussels, and scallops • They have a shell divided into two halves drawn together by adductor muscles • Some bivalves have eyes and sensory tentacles along the edge of their mantle © 2011 Pearson Education, Inc. Figure 33.19 • The mantle cavity of a bivalve contains gills that are used for feeding as well as gas exchange © 2011 Pearson Education, Inc. Figure 33.20 Mantle Hinge area Coelom Gut Heart Digestive gland Adductor muscle (one or two) Anus Mouth Excurrent siphon Shell Palp Foot Mantle cavity Gonad Gill Water flow Incurrent siphon Cephalopods • Cephalopods are carnivores with beak-like jaws surrounded by tentacles of their modified foot • Most octopuses creep along the sea floor in search of prey © 2011 Pearson Education, Inc. Figure 33.21 Squid Octopus Chambered nautilus Figure 33.21a Squid • Squids use their siphon to fire a jet of water, which allows them to swim very quickly © 2011 Pearson Education, Inc. Figure 33.21b Octopus • One small group of shelled cephalopods, the nautiluses, survives today © 2011 Pearson Education, Inc. Figure 33.21c Chambered nautilus • Cephalopods have a closed circulatory system, well-developed sense organs, and a complex brain • Shelled cephalopods called ammonites were common but went extinct at the end of the Cretaceous 65.5 million years ago © 2011 Pearson Education, Inc. Protecting Freshwater and Terrestrial Molluscs • Molluscs are the animal group with the largest number of recent extinctions • The most threatened groups are – Freshwater bivalves, including pearl mussels – Terrestrial gastropods, including Pacific island land snails • These molluscs are threatened by habitat loss, pollution, and non-native species © 2011 Pearson Education, Inc. Figure 33.22 Other invertebrates Molluscs Amphibians Insects Birds Fishes Mammals An endangered Pacific island land snail, Partula suturalis Recorded extinctions of animal species (Data: International Union for Reptiles (excluding birds) Conservation of Nature, 2008) Workers on a mound of pearl mussels killed to make buttons (ca. 1919) Figure 33.22a An endangered Pacific island land snail, Partula suturalis Figure 33.22b Molluscs Other invertebrates Amphibians Insects Fishes Mammals Recorded extinctions of animal species (Data: International Union for Conservation of Nature, 2008) Birds Reptiles (excluding birds) Figure 33.22c Workers on a mound of pearl mussels killed to make buttons (ca. 1919) Annelids • Annelids have bodies composed of a series of fused rings • Annelids are coelomates • The phylum Annelida is divided into two groups – Polychaeta (polychaetes) – Oligochaeta (earthworms and their relatives, and leeches) © 2011 Pearson Education, Inc. Polychaetes • Members of class Polychaetes have paddle-like parapodia that work as gills and aid in locomotion • Most polychaetes are marine © 2011 Pearson Education, Inc. Figure 33.23 Parapodia Oligochaetes • Oligochaetes (class Oligochaeta) are named for relatively sparse chaetae, bristles made of chitin © 2011 Pearson Education, Inc. Earthworms • Earthworms eat through soil, extracting nutrients as the soil moves through the alimentary canal • Earthworms are hermaphrodites but cross-fertilize • Some reproduce asexually by fragmentation © 2011 Pearson Education, Inc. Figure 33.24 Cuticle Coelom Epidermis Septum (partition between segments) Circular muscle Metanephridium Longitudinal muscle Anus Dorsal vessel Chaetae Intestine Skin Ventral vessel Fused nerve cords Nephrostome Metanephridium Clitellum Esophagus Crop Pharynx Intestine Giant Australian earthworm Gizzard Cerebral ganglia Mouth Subpharyngeal ganglion Circulatory system vessels Ventral nerve cords with segmental ganglia Figure 33.24a Giant Australian earthworm Figure 33.24b Cuticle Epidermis Circular muscle Coelom Septum (partition between segments) Metanephridium Longitudinal muscle Anus Dorsal vessel Chaetae Intestine Fused Ventral vessel nerve cords Nephrostome Figure 33.24c Anus Skin Metanephridium Clitellum Esophagus Crop Pharynx Gizzard Cerebral ganglia Mouth Intestine Subpharyngeal Circulatory ganglion system vessels Ventral nerve cords with segmental ganglia Leeches • Most species of leeches live in fresh water; some are marine or terrestrial • Leeches include predators of invertebrates, and parasites that suck blood • Leeches secrete a chemical called hirudin to prevent blood from coagulating © 2011 Pearson Education, Inc.