Transcript Protostomes
The Animal Kingdom: The Protostomes Chapter 30 Learning Objective 1 • Cite specific examples of the evolutionary significance of the coelom Coelom 1 • True coelom is a fluid-filled body cavity • • completely lined by mesoderm between digestive tube and outer body wall Allows tube-within-a-tube body plan • • body wall is outer tube inner tube is digestive tube Coelom 2 • An enclosed compartment (or series of compartments) of fluid under pressure • Serve as hydrostatic skeleton • contracting muscles push against tube of fluid Coelom 3 • A space in which internal organs develop • including gonads • Helps transport materials • Protects internal organs KEY CONCEPTS • Evolution of the coelom has been associated with important innovations in body plan, including cephalization, the tube-within-a-tube body plan, compartmentalization, and segmentation Learning Objective 2 • Characterize the protostomes • Describe their two main evolutionary branches • Give examples of animals assigned to each branch Protostomes • Characterized by • • • spiral cleavage determinate cleavage development of mouth from blastopore Two Branches of Protostomes • Lophotrochozoa • • platyhelminths, nemerteans, mollusks, annelids, lophophorate phyla, rotifers Ecdysozoa • nematodes (roundworms) and arthropods KEY CONCEPTS • Protostomes are a monophyletic group that gave rise to two major clades: Lophotrochozoa and Ecdysozoa Learning Objective 3 • What are the distinguishing characteristics of phylum Nemertea and phylum Platyhelminthes? • Describe the main classes of phylum Platyhelminthes, giving examples of animals that belong to each class Phylum Nemertea (Ribbon Worms) 1 • Characterized by proboscis • • muscular tube for capturing food, defense Reduced coelom (rhynchocoel) • space surrounding proboscis Phylum Nemertea (Ribbon Worms) 2 • Nemerteans have • • • tube-within-a-tube body plan complete digestive tract with mouth and anus a circulatory system Nemerteans Phylum Platyhelminthes (Flatworms) 1 • Acoelomate animals with • • • • • bilateral symmetry cephalization 3 definite tissue layers well-developed organs Many are hermaphrodites • single animal produces both sperm and eggs Phylum Platyhelminthes (Flatworms) 2 • Ladder-type nervous system • • • • sense organs simple brain composed of two ganglia 2 nerve cords that extend the length of body Protonephridia • function in osmoregulation and disposal of metabolic wastes 3 Classes of Phylum Platyhelminthes • Class Turbellaria • • Classes Trematoda and Monogenea • • free-living flatworms, including planarians parasitic flukes Class Cestoda • parasitic tapeworms Planarian Deuterostomia Ecdysozoa Rotifera Lophophorate phyla Annelida Mollusca Nemertea Platyhelminthes Radiata Parazoa Lophotrochozoa Choanoflagellate ancestor Fig. 30-1 (1), p. 642 Ganglia Auricle Auricle Eyespot Nerve Gastrovascular cavity Pharynx Sheath surrounding pharynx Mouth 1 mm Fig. 30-1ab, p. 642 Pharyngeal sheath cavity Pharyngeal cavity Inner muscle layer of pharynx Outer muscle layer Muscle Epidermis Sperm mass Ventral nerve cords Adhesive gland Cilia Muscle layers Body wall composed of epidermis, circular muscle, and longitudinal muscle Fig. 30-1c, p. 642 Insert “Planarian organ systems” planarian_organs_v2.swf Parasitic Flukes and Tapeworms • Typically have suckers or hooks • • for holding on to their hosts Have complicated life cycles • • intermediate hosts large numbers of eggs Parasitic Fluke 2 Larvae make their way to circulatory system, where they mature. During reproduction, which takes place in veins, male holds female in a long groove. 1 Larvae burrow through skin. 1 mm 3 Eggs pass into intestine. 7 Finally, forktailed larvae (cercariae) develop and leave snail. 4 Eggs containing developing embryos are excreted with feces. 6 Larvae must enter a second host, a freshwater snail. After burrowing into tissues of snail, larvae develop into a form that reproduces asexually. 5 If they find their way to fresh water, the eggs hatch, releasing free-swimming larvae (miracidia). Fig. 30-2, p. 644 Tapeworm Insert “Blood fluke lifecycle” and “Tapeworm life cycle” blood_fluke.swf tapeworm.swf Watch the fluke and tapeworm life cycles by clicking on the figures in ThomsonNOW. Learning Objective 4 • What are the adaptive advantages of cephalization? Cephalization • Evolution of a head • • • concentration of sense organs and nerve cells (simple brain) at anterior end (Flatworms show beginnings of cephalization) Increases effectiveness of bilateral animal • • to actively find food, shelter, mates to detect enemies Learning Objective 5 • What are the distinguishing characteristics of phylum Mollusca and the four molluscan classes discussed? • Give examples Phylum Mollusca • Soft-bodied animals • • Ventral foot • • usually covered by a shell for locomotion Mantle • covers visceral mass (body organs) Mollusks • Most have open circulatory system • • Most have rasplike radula for feeding • • Cephalopods have closed circulatory system Bivalves are suspension feeders Most marine mollusks have freeswimming, ciliated trochophore larva Insert “Molluscan classes” mollusk_classes.swf Trochophore Larva Digestive tract Cilia Mouth Nephridium Mesodermal cells Anus Fig. 30-7, p. 648 Class Polyplacophora • • Includes marine chitons Shells consist of 8 overlapping plates Shell Digestive tract Class Polyplacophora Fig. 30-6a, p. 647 Class Gastropoda • Largest group of mollusks • • snails, slugs, and their relatives Body undergoes torsion • a twisting of the visceral mass Shell Foot Digestive tract Class Gastropoda Fig. 30-6b, p. 647 Insert “Snail body plan” snail_body_plan.swf Torsion Insert “Torsion in gastropods” torsion.swf Class Bivalvia • Includes aquatic clams, scallops, oysters • Two-part shell • • • hinged dorsally encloses bodies Suspension feeders Shell Digestive Foot tract Class Bivalva Fig. 30-6c, p. 647 Clam Heart Digestive gland Stomach DORSAL Metanephridium Intestine Esophagus Posterior adductor muscle Anus Ganglion Anterior adductor muscle Excurrent siphon Incurrent siphon Mouth Palp Pedal ganglion Gill—partially cut Mantle Foot Shell Intestine Gonad VENTRAL Fig. 30-10, p. 649 Insert “Clam body plan” clam.swf Class Cephalopoda • Includes squids, octopods, Nautilus • Active, predatory swimmers • Tentacles surround the mouth • located in the large head Tentacles (modified foot) Internal shell Digestive tract Class Cephalopoda Fig. 30-6d, p. 647 Learning Objective 6 • What are the distinguishing characteristics of phylum Annelida and the three annelid classes discussed? • Give examples Phylum Annelida (Segmented Worms) • Aquatic worms, earthworms, leeches • Conspicuously long bodies • Segmentation • • both internally and externally Large, compartmentalized coelom • serves as hydrostatic skeleton Annelids Mouth Setae Clitellum Suckers Parapodia Anus Class Polychaeta Class Oligochaeta Class Hirudinea Fig. 30-11 (a-c), p. 650 Setae Deuterostomia Ecdysozoa Rotifera Lophophorate phyla Annelida Mollusca Nemertea Platyhelminthes Radiata Parazoa Lophotrochozoa Mouth Clitellum Suckers Parapodia Choanoflagellate ancestor Anus Class Polychaeta Class Oligochaeta Class Hirudinea Stepped Art Fig. 30-11 (a-c), p. 650 Earthworm Clitellum Intestine Gizzard Crop Esophagus Pharynx Dorsal vessel Ventral vessel Muscles Longitudinal Circular Septa Nerve cord Mouth Cerebral ganglia Fig. 30-12a, p. 651 Intestine Dorsal blood vessel Metanephridia Coelom Ventral blood vessel Nerve cord Fig. 30-12b, p. 651 Insert “Earthworm body plan” earthworm_v2.swf Leeches Class Polychaeta • Marine worms with parapodia • appendages for locomotion, gas exchange • Parapodia have many setae • Well-defined head with sense organs • unlike other annelids Class Oligochaeta • Earthworms • Characterized by few short setae per segment • Body divided into > 100 segments • separated internally by septa Class Hirudinea • Leeches • Characterized by absence of setae and appendages • Parasitic leeches have suckers • for holding on to their host Learning Objective 7 • What are the distinguishing characteristics of the lophophorate phyla? The Lophophorate Phyla • Marine animals with a lophophore • • brachiopods, phoronids, bryozoans Lophophore • • ciliated ring of tentacles surround the mouth specialized to capture particles in water Lophophorates • Phylum Brachiopoda • Phylum Phoronida • Phylum Bryozoa Deuterostomia Ecdysozoa Rotifera Lophophorate phyla Annelida Mollusca Nemertea Platyhelminthes Radiata Parazoa Lophotrochozoa Choanoflagellate ancestor Fig. 30-14 (1), p. 653 Phylum Rotifera Deuterostomia Ecdysozoa Rotifera Lophophorate phyla Annelida Mollusca Nemertea Platyhelminthes Radiata Parazoa Lophotrochozoa Choanoflagellate ancestor Fig. 30-15 (1), p. 654 150 µm Fig. 30-15a, p. 654 Crown of cilla Mouth Eyespot Pharynx (grinding organ) Digestive glands Stomach Reproductive organ Protonephridium Intestine Bladder Anus Cuticle and epidermis Fig. 30-15b, p. 654 Learning Objective 8 • What are the distinguishing characteristics of phylum Nematoda? Phylum Nematoda (Roundworms) • Highly successful ecdysozoans • Pseudocoelom • Body covered by tough cuticle • helps prevent desiccation Phylum Nematoda (Roundworms) • Parasitic nematodes in humans • • • • Ascaris hookworms trichina worms pinworms Ascaris Mouth Pharynx Dorsal nerve Excretory canal Excretory gland Pharynx Muscle of pharynx wall Pseudocoelom Uterus Ovary Intestine Excretory canal Vulva Muscle layer Ventral nerve Epidermis Cuticle (b) Cross section Anus (a) Longitudinal section Fig. 30-17, p. 656 Learning Objective 9 • What are the distinguishing characteristics of phylum Arthropoda? • Distinguish among the subphyla and classes of this phylum • Give examples of animals that belong to each group Phylum Arthropoda 1 • Segmented animals with paired, jointed appendages • Armorlike exoskeleton of chitin • Molting necessary for arthropod to grow Phylum Arthropoda 2 • Open circulatory system • dorsal heart, pumps hemolymph • Aquatic forms have gills for gas exchange • Terrestrial forms have either tracheae or book lungs KEY CONCEPTS • The most biologically successful protostomes in terms of diversity and numbers are the mollusks and the arthropods Trilobites • Extinct marine arthropods • • covered by hard, segmented shell Each segment had a pair of biramous appendages with two jointed branches • • inner walking leg outer gill branch Trilobites Deuterostomia Arthropoda Nematoda Lophotrochozoa Radiata Parazoa Ecdysozoa Choanoflagellate ancestor Fig. 30-19 (1), p. 658 Antenna Head Eye Gill Lateral lobe Median lobe (a) Dorsal view of a trilobite. (b) Ventral view. Fig. 30-19ab, p. 658 Subphylum Myriapoda • 2 Classes • • Chilopoda (centipedes) Diplopoda (millipedes) • Uniramous (unbranched) appendages • Single pair of antennae Myriapods Subphylum Chelicerata 1 • Merostomes (horseshoe crabs) and Arachnids (spiders, mites, and relatives) • Body with cephalothorax and abdomen • 6 pairs of uniramous, jointed appendages • 4 pairs serve as legs Subphylum Chelicerata 2 • First appendages are chelicerae • second are pedipalps • Appendages adapted for manipulation of food, locomotion, defense, copulation • No antennae, no mandibles Chelicerates Subphylum Crustacea 1 • Lobsters, crabs, shrimp, pill bugs, barnacles • Body with cephalothorax and abdomen • Most have five pairs of walking legs • Appendages are biramous Subphylum Crustacea 2 • Two pairs of antennae • • Third appendages are mandibles • • sense taste and touch for chewing Two pairs of maxillae • • posterior to mandibles manipulate and hold food Crustaceans Lobster Cephalothorax Abdomen Thorax Head Eye Fifth walking leg Fig. 30-23a, p. 661 Tail fan Fifth walking leg Second walking leg Mouth Third maxilliped Cheliped First antenna Second antenna Swimmerets First swimmeret (used by male in copulation) Fig. 30-23b, p. 661 Subphylum Hexapoda • Includes class Insecta • articulated, tracheated hexapods Head Thorax Abdomen Forewing Antenna Simple eye Compound eye Sound receptor Spiracles Hindwing (a) External structure. Note the three pairs of segmented legs. Fig. 30-24a, p. 661 Insects • • • • • Body with head, thorax, and abdomen Uniramous appendages Single pair of antennae Tracheae for gas exchange Malpighian tubules for excretion Grasshopper Ovary Digestive gland Heart Anus Brain Nerve cord Malpighian tubules (b) Internal Anatomy. Intestine Genital opening Learning Objective 10 • What adaptations have contributed to the biological success of insects? Insect Adaptations 1 • • • • • Versatile exoskeleton Segmentation Specialized jointed appendages Highly developed sense organs Ability to fly Insert “Insect head parts” insect_heads.swf Insect Adaptations 2 • Metamorphosis • • transition from one developmental form to another reduces intraspecific competition Metamorphosis Insert “Insect development” insect_devt.swf Insect Adaptations 3 • Insects have developed • • • effective reproductive strategies effective mechanisms for defense, offense ability to communicate KEY CONCEPTS • The remarkable biological success of the insects can be attributed to the evolution of complex body plans and life cycles, for example, their exoskeleton, segmentation, specialized jointed appendages, ability to fly, and metamorphosis Explore the body plans of the protostomes by clicking on the figures in ThomsonNOW.