Animal Evolution and Invertebrates

Learning objectives Parazoa 1. From a diagram, identify the parts of a sponge (including the spongocoel, porocyte, epidermis, choanocyte, mesohyl, amoebocyte, osculum, and spicule) and describe the function of each. Radiata 2. List the characteristics of the phylum Cnidaria that distinguish it from the other animal phyla. 3. Describe the two basic body plans in Cnidaria and their role in Cnidarian life cycles. 4. List the three classes of Cnidaria and distinguish among them based on life cycle and morphological characteristics. 5. List the characteristics of the phylum Ctenophora that distinguish it from the other animal phyla. Lophotrochozoa 6. Distinguish between the following pairs: bilateria and urbilateria, acoelomates and coelomates, protostomes and deuterostomes, and Lophotrochozoa and Ecdysozoa. 7. List the characteristics of the phylum Platyhelminthes that distinguish it from the other animal phyla. 8. Distinguish among the four classes of Platyhelminthes and give examples of each. 9. Describe the generalized life cycle of a trematode and give an example of one fluke that parasitizes humans. 10. Describe the anatomy and generalized life cycle of a tapeworm. 11. Describe unique features of rotifers that distinguish them from other pseudocoelomates. 12. Define parthenogenesis and describe alternative forms of rotifer reproduction 13. Define lophophore and list three lophophorate phyla. 14. List the distinguishing characteristics of the phylum Nemertea. 15. Explain the relationship between proboscis worms and flatworms. 16. List the characteristics that distinguish the phylum Mollusca from the other animal phyla. 17. Describe the basic body plan of a mollusk and explain how it has been modified in the Bivalvia, Cephalopoda, Gastropoda, and Polyplacophora. 18. Distinguish among the following four molluscan classes and give examples of each: a. Bivalvia b. Cephalopoda c. Gastropoda d. Polyplacophora 19. List the characteristics that distinguish the phylum Annelida from the other animal phyla. 20. Distinguish among the classes of Annelida and give examples of each. 21. Describe the adaptive advantage of a coelom and segmentation in annelids. Ecdysozoa 22. List the characteristics of the phylum Nematoda that distinguish it from other wormlike animals. 23. Give examples of both parasitic and free-living species of nematodes. 24. List the characteristics of arthropods that distinguish them from the other animal phyla. 25. Describe advantages and disadvantages of an exoskeleton. 26. Distinguish between hemocoel and coelom. 27. Define and distinguish between the major independent arthropod lines of evolution represented by: a. Trilobita b. Chelicerata c. Crustacea d. Uniramia 28. Describe the different views regarding the relationship between arthropods and annelids. 29. Describe the basic mechanism for the development of segmented bodies. 30. Describe three hypotheses that can account for the scattered distribution of segmentation in animals. Deuterostomia 31. List the characteristics of echinoderms that distinguish them from other animal phyla. 32. Distinguish among the five classes of echinoderms and give examples of each. 33. Explain why the phylum Chordata is included in a chapter on invertebrates. 34. Describe the evolutionary relationships between echinoderms and chordates. Summary of Key Concepts

PARAZOA

 Phylum Porifera: Sponges are sessile with porous bodies and choanocytes. Sponges lack tissues and organs. They filter-feed by drawing water through pores; choanocytes (flagellated collar cells) ingest bacteria and particulate food suspended in the water. RADIATA

 Phylum Cnidaria: Cnidarians have radial symmetry, a gastrovascular cavity, and cnidocytes. Cnidarians are mainly marine carnivores possessing tentacles armed with cnidocytes that aid in defense and the capture of prey. Two body forms are sessile polyps and floating medusas. The digestive tract (gastrovascular cavity) is incomplete (has a single opening, the mouth, that also functions as an anus). Class Hydrozoa usually alternates polyp and medusa forms, although the polyp is more conspicuous. In class Scyphozoa, jellies (medusas) are the prevalent forms of the life cycle. Class Anthozoa contains the sea anemones and corals, which occur only as polyps.  Phylum Ctenophora: Comb jellies possess rows of ciliary plates and adhesive colloblasts. Comb jellies use retractable tentacles to capture food.

PROTOSTOMIA: LOPHOTROCHOZOA

 Phylum Platyhelminthes: Flatworms are acoelomates with gastrovascular cavities. Most flatworms are ribbonlike animals with a gastrovascular cavity. Class Turbellaria is made up of mostly free-living, primarily marine species. Members of the classes Trematoda and Monogenea live as parasites in or on animals. Class Cestoidea (tapeworms), all parasites, lack a digestive tract.  Phylum Rotifera: Rotifers are pseudocoelomates with jaws, crowns of cilia, and complete digestive tracts. Found mainly in fresh water, many rotifer species are parthenogenetic.  The lophophorate phyla: Bryozoans, phoronids, and brachiopods are coelomates with ciliated tentacles around their mouths. The lophophore is a horseshoe-shaped, suspension-feeding organ bearing ciliated tentacles.  Phylum Nemertea: Proboscis worms are named for their preycapturing apparatus. The proboscis worms have a unique retractable tube (proboscis) used for defense and prey capture. A fluid-filled cavity surrounds the proboscis.  Phylum Mollusca: Mollusks have a muscular foot, a visceral mass, and a mantle. Class Polyplacophora is composed of the chitons, oval-shaped marine animals encased in an armor of dorsal plates. Most members of class Gastropoda, the snails and their relatives, possess a single, spiraled shell; sea slugs lack a shell; embryonic torsion of the body is a distinctive characteristic. Class Bivalvia (clams and their relatives) have hinged shells divided into two halves. Class Cephalopoda includes squids and octopuses, carnivores with beaklike jaws surrounded by tentacles of the modified foot.  Phylum Annelida: Annelids are segmented worms. Class Oligochaeta includes earthworms and various aquatic species. Members of class Polychaeta possess paddlelike parapodia that function as gills and aid in locomotion. Class Hirudinea consists of the leeches.

PROTOSTOMIA: ECDYSOZOA  Phylum Nematoda: Roundworms are nonsegmented pseudocoelomates covered by tough cuticles. Among the most widespread and numerous animals, nematodes inhabit most aquatic habitats. Some species are important parasites of animals and plants.  Arthropods are segmented coelomates with exoskeletons and jointed appendages. There are more known species of arthropods than all other phyla combined. Chelicerates, arthropods with pincer or fanglike feeding appendages, include class Arachnida (spiders, ticks, scorpions, and mites). A traditional classification scheme groups the insects (class Insecta), centipedes (class Chilopoda), and millipedes (class Diplopoda) as uniramians--all with one pair of antennae and unbranched (uniramous) appendages. Crustaceans (lobsters, crayfish, crabs, shrimps, and barnacles) are primarily aquatic arthropods with two pairs of antennae and branched appendages. Research on the origin of segmentation in arthropods and other phyla of segmented animals will help systematists test hypotheses about phylogeny.

DEUTEROSTOMIA

 Phylum Echinodermata: Echinoderms have a water vascular system and secondary radial anatomy. Sea stars and their relatives make up six classes of the marine phylum Echinodermata. The radial anatomy of many species evolved secondarily from bilateral ancestors. The vascular system ending in tube feet is used for locomotion and feeding. A thin, bumpy, or spiny skin covers a calcareous endoskeleton.

Phylum Chordata: The chordates include two invertebrate subphyla and all vertebrates. Chordates share many features of embryonic development with the echinoderms.

Key Terms ammonites brachiopod amoebocyte bryozoan antennae cephalization Arthropoda chelicerae arthropods chelicerates book lungs choanocyte bilateral symmetry class Arachnida blastula class Chilopoda cleavage mantle cavity class Diplopoda mantle class Insecta medusa closed circulatory system mesoderm cnidocytes mesohyl coelom metanephridium colloblasts metamorphosis complete digestive tract molting complete metamorphosis nematocysts compound eye open circulatory system copepods osculum crustacean parthenogenesis cuticle phoronids decapod phylum Chelicerata echinoderms phylum Crustacea ectoderm phylum Trilobita endoderm phylum Uniramia entomology planarians eurypterid polyp exoskeleton psuedocoelom foot radula gastrovascular cavity radial symmetry gatrula spongocoel gastrulation torsion hermaphrodite tracheal system incomplete metamorphosis trilobites invertebrates trochophore isopods tube feet lophophorate animals uniramians lophophore urbilateria malpighian tubule visceral mass mandibles water vascular system

QUESTIONS – Reading Chapter 18 and provided lab materials will help! 1. What are bilateral symmetry and cephalization? 2. Draw a phylogenetic tree for animals showing sponges, cnidarians, flatworms, nematodes, molluscs, annelids, arthropods, echinoderms and chordates. 3. Explain how the animal kingdom is divided on the basis of symmetry, body cavities, and embryology; list the major phyla within each major subdivision. 4. Discuss the advantages of bilateral symmetry over radial symmetry. 5. Describe the differences between the protostomes and the deuterostomes. (Check out the chart on page 369). 6. Describe main characteristics of the Porifera (sponges). 7. Describe the distinguishing characteristics of the Cnidaria (focus in on gastrovascular cavity). 8. Describe the major characteristics of the Platyhelminthes. 9. Describe the tapeworm's special adaptation for parasitism. 10. List the identifying features of the nematodes and discuss the economic importance of this phylum. 11. Why are the annelids, arthropods and molluscs thought to be closely related? 12. Describe the body plan common to all Mollusca, and indicate the modifications it exhibits in the Gastropoda (snails), Bivalvia (bivalves), and Cephalopoda (squids and octopuses). 13. Describe the distinguishing characteristics of the Annelidia, and compare the polychaetes, the earthworms, and the leeches with respect to the presence or absence of a distinct head, the degree of segmentation, the presence or absence of parapodia, and the presence of setae, or bristles. 14. Describe the distinguishing characteristics of the arthropods. 15. Describe the distinguishing characteristics of the Crustacea, Chilopoda, Diplopoda, Insecta, and Arachnida. List representative examples of each. 16. Briefly describe the structure of the generalized insect body. (Figure 18.12B) 17. Contrast complete and incomplete metamorphosis. 18. Name the two major phyla of the Deuterostomia, and list representative examples of each. 19. Describe the distinguishing characteristics of the echinoderms, and list a representative example of each class. 20. What four features distinguish Chordata.