BLY 122 Lecture Notes (O’Brien) 2010 XII. Chapter 33— Protostome Animals I. Key Concepts A. Monophyletic group with 2 main subgroups 1. Lophotrochozoa 2. Ecdysozoa B. Phyla with greatest diversity in species & body plans 1. Mollusca (Lophotrochozoa) 2. Arthropoda (Ecdysozoa) C. Key events in evolution 1. Several lineages independently moved from water to land 2. Diversification of appendages and mouth parts 3. Metamorphosis in both marine & terrestrial forms II. Introduction A. Arthropods are the most abundant animals on earth (Fig. 33.2 ) B. Important model organisms ( Fig. 33.1 ) 1. Fruit fly Drosophila melanogaster a. Genetics b. Cheap and easy to maintain in lab 2. Roundworm Caenorhabditis elegans a. Developmental biology b. History of all 959 adult cells known III. An Overview of Protostome Evolution (33.1 ) A. Analyzing Morphological Traits 1. All protostome embryos experience similar embryonic development: a. They have a spiral cleavage pattern. b. They develop a mouth from the first invagination during gastrulation. 2. All protostomes are triplobastic 3. Bilaterally symmetrical 4. Many protostomes are segmented : Bodies are a series of compartments with repeated structures B What is a Lophotrophozoan? (Fig. 33.4) 1. LOPHOPHORE; Feeding structure found in 3 (not all) phyla in group 2. TROCHOPHORE: Larval stage found in many (not all) phyla in group C. What is an Ecdysozoan? (Fig. 33.5) 1. Grow by molting (= ecdysis) 2. Nematodes covered with a cuticle 3. Arthropods covered with an exoskeleton IV. Themes in the Diversification of Protostomes (33.2) A. How Do Body Plans Vary among Phyla? (Fig. 33.6) 1. Platyhelminthes (flatworms) have the ACOELOMATE body plan. 34 2. Nematodes (roundwoms) have a PSEUDOCOELOM: gut not enveloped with mesoderm 3. The Arthropod Body Plan a. EXOSKELETON of CHITIN hardened by calcium carbonate (Fig.33.7a) b. Move using JOINTED APPENDAGES c. Segmentation usually obvious 4. The Molluscan Body Plan a. Muscular FOOT used for movement b. VISCERAL MASS contains the internal organs and external gills c. The MANTLE covers the visceral mass. ( Fig. 33.7b) b. Often protected by a calcium carbonate SHELL secreted by the mantle. B. The Water to Land Transition 1. Occurred many times in protostome phyla a. Arthropods (twice) b. Mollusks 2. Possession of appendages, hydrostatic skeleton & exoskeleton made transition easier for protostomes than plants 3. Gas exchange organs and prevention of desiccation were important adaptations [ADAPTATION: trait that increases the fitness of individuals relative to other individuals without that trait] C. How Do Protostomes Feed, Move & Reproduce? 1. Adaptations for Feeding a. Tremendous diversity b. Result of metamorphosis: larvae and adults feed in different habitats, thus, do not compete with one another 2. Adaptations for Moving a. Wormlike protostomes w/o limbs use hydrostatic skeleton b. About 2/3 rd multicellular species are winged insects ( Fig. 33.10b) c. Mollusks (1) Waves of muscle contractions in foot allow gliding ( Fig. 33.10c ) (2) JET PROPULSION: Contraction of muscles in mantle force water out SIPHON in squid and octopus ( Fig. 33.10d ) 3. Adaptations for Reproduction a. PARTHENOGENESIS: Offspring develop from unfertilized eggs b. Sexual reproduction most common c. Two unique reproductive innovations (1) Metamorphosis (a) Enhances dispersal of sessile marine organisms (b) Reduces intra-specific competition in terrestrial organisms (2) Eggs that do not dry out (= resist desiccation) V. Key Lineages of Lophotrochozoans (33.3) A. Lophophozoans 1. Rotifers ( Fig. 33.12 ) a. Feed with cluster of cilia whose movement resembles a rotating sphere b. Sexual reproduction has never been observed in this group 2. Platyhelminthes (Flatworms) ( Fig. 32.13a-c) a. Parasitic species with complex life-cyles involving many hosts b. Trematodes = flukes c. Tapeworms 35 C Annelida (Segmented Worms) ( Fig. 33.14) a. Earthworms b. Leeches D. Mollusca (Mollusks) 1. Bivalves (Clams, Mussels, Scallops, Oysters) ( Fig. 33.15) a. Two shells b. Filter feeders 2. Gastropoda (Snails & Slugs) a. Mouth structure called a RADULA is used to scrape algae off rocks or bore holes into shells of prey ( Fig. 33.16 ) b. Move using wavelike foot contractions. ( Fig. 33.10c) 3. Cephalopoda (Squid, Nautilus, Octopuses) ( Fig. 33.18) a. Most intelligent of the invertebrates b. Well-developed eyes c. Move via jet propulsion. ( Fig. 33.10d) d. Predators VI. Key Lineages of Ecdysozoans (33.4) A. Ecdysozoans grow by MOLTING—shedding their soft cuticle or hard exoskeletons—then they secrete a new one to fit the bigger body. ( Fig. 33.5) B. Nematoda (Roundworms) ( Fig. 33.21) 1. Unsegmented worms with a pseudocoelom. 2. Model organism Caenorhabditis elegans 3. Some are important parasites of humans a. Hookworms b. Ascaris c. Riverblindness cause C. Arthropoda 1. What do all arthropods have in common? a. Segmented bodies with reduced coeloms. b. Paired, segmented appendages 2. Chelicerates (Spiders, Ticks, Mites, Horseshoe Crabs & Scorpions) a. CHELICERAE: A pair of mouth appendages that move up and down. b. Two body regions. Fig. 33.23a ) c. Mites and ticks are ectoparasites of animals. Fig. 32.23b) 3. Insecta (Insects) ( Fig. 32.25 ) a. 3 PAIRS OF LEGS. b. Adults have 2 pairs of wings. c. Three body regions: HEAD, THORAX AND ABDOMEN d. Metamorphosis e. MANDIBLES: a pair of mouth appendages that move sideways 4. Crustaceans (Shrimp, Lobster, Crabs, Barnacles) ( Fig. 33.24) a. Barnacles use feathery appendages to capture small swimming prey. b. MANDIBLES 36 .