• 1.08k likes • 1.09k Views
Learn about coelom's evolutionary importance, protostomes, and distinguishing features of nemerteans and flatworms, with examples from Mollusca and class Turbellaria.
E N D
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-tubebody 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
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 ofPhylum Platyhelminthes • Class Turbellaria • free-living flatworms, including planarians • Classes Trematoda and Monogenea • parasitic flukes • Class Cestoda • parasitic tapeworms
Lophotrochozoa Lophophorate phyla Platyhelminthes Deuterostomia Ecdysozoa Nemertea Mollusca Annelida Parazoa Rotifera Radiata 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 Inner muscle layer of pharynx Pharyngeal cavity Outer muscle layer Muscle Epidermis Adhesive gland Sperm mass Ventral nerve cords Cilia Body wall composed of epidermis, circular muscle, and longitudinal muscle Muscle layers 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
Larvae make their way to circulatory system, where they mature. During reproduction, which takes place in veins, male holds female in a long groove. 2 1 Larvae burrow through skin. 1 mm 3 Eggs pass into intestine. 7 Finally, fork-tailed 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
Insert “Blood fluke life-cycle” 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
PhylumMollusca • Soft-bodied animals • usually covered by a shell • Ventral foot • for locomotion • Mantle • covers visceral mass (body organs)
Mollusks • Most have open circulatory system • Cephalopods have closed circulatory system • Most have rasplike radula for feeding • Bivalves are suspension feeders • Most marine mollusks have free-swimming, ciliated trochophore larva
Insert “Molluscan classes” mollusk_classes.swf
Digestive tract Cilia Mouth Nephridium Mesodermal cells Anus Fig. 30-7, p. 648
ClassPolyplacophora • Includes marine chitons • Shells consist of 8 overlapping plates
Shell Digestive tract Class Polyplacophora Fig. 30-6a, p. 647
ClassGastropoda • Largest group of mollusks • snails, slugs, and their relatives • Body undergoes torsion • a twisting of the visceral mass
Shell Digestive tract Foot Class Gastropoda Fig. 30-6b, p. 647
Insert “Snail body plan” snail_body_plan.swf
Insert “Torsion in gastropods” torsion.swf
ClassBivalvia • Includes aquatic clams, scallops, oysters • Two-part shell • hinged dorsally • encloses bodies • Suspension feeders
Shell Digestive tract Foot Class Bivalva Fig. 30-6c, p. 647
Heart Digestive gland DORSAL Metanephridium Stomach Intestine Esophagus Posterior adductor muscle Ganglion Anus Anterior adductor muscle Excurrent siphon Mouth Incurrent siphon Palp Gill—partially cut Pedal ganglion Mantle Foot Shell Intestine Gonad VENTRAL Fig. 30-10, p. 649
Insert “Clam body plan” clam.swf
ClassCephalopoda • 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