Biology, 9th ed, Sylvia Mader Chapter 29 Chapter 29 Introduction to Invertebrates Introduction to Invertebrates

Animals What makes an animal? How can you tell if something is an animal or not? What are some examples of animals?

Evolution of Animals (intro) All animals are multicellular heterotrophic organisms that must take in preformed food. mulitcellular: made of more than one cell heterotrophic: take in preformed food from other organisms food: complex organic molecules; often glucose related compounds

Criteria for the Evolution of Animals 1. Multicellularity Outline Criteria for the Evolution of Animals 1. Multicellularity 2. True Tissues 3. Bilateral Symmetry 4. Body Cavities 5. The Coelom 6. Segmentation 7. Development

Evolution of Animals (intro) All animals are multicellular heterotrophic organisms that must take in preformed food Classification Criteria Level of organization Cellular, tissue, organ Body Plan Sac, tube-within-a-tube Segmentation Segmentation leads to specialization

Evolution of Animals (intro) Classification Criteria, cont Symmetry Radial - Two identical halves Bilateral - Definite right and left halves Type of Coelom Acoelomate Pseudocoelom Coelom Early Developmental Pattern Protostome - First embryonic opening becomes the mouth Dueterostome - Second embryonic opening becomes the mouth

Animals: How does this picture demonstrate that an animal is involved?

Traditional Phylogenetic Tree of Animals

Animal? In order to be considered an animal, what must be true about this organism?

Multicellularity Sponges Only level of animal to have cellular organization Saclike bodies perforated by many pores Beating of flagella produces water currents that flow through pores into central cavity and out osculum Sessile filter feeders Asexual reproduction by fragmentation or budding

Simple Sponge Anatomy

Porifera in the Animal Cladogram Sponges sitting at the bottom of the animal phylogeny simplest of the existing animals and possibly one of the simplest of all time

True Tissue Layers – Ctenophora & Cnidarians Many animals have a total of three possible germ layers Ectoderm – outside layer; skin or outer covering , brain and peripheral nerves Endoderm – inside layer; gut track and some digestive tissues Mesoderm – inner layer; muscles phlya Ctenophora and Cnidaria develop only ectoderm and endoderm Diploblasts – animals derived from only 2 embryonic layers Radially symmetrical

True Tissue Layers phlya Ctenophora and Cnidaria develop only ectoderm and endoderm So what is in the middle if these organisms (the first with true tissue layers) ? What are Ctenophora called again?

Types of Symmetry

Comb Jellies - Ctenophora Characteristics: Small, transparent, and often luminescent Most of body composed of mesoglea Largest animals propelled by beating of cilia Capture prey with tentacles

Comb Jelly Compared to Cnidarian

Tubular animals that most often reside in shallow marine waters Cnidarians Tubular animals that most often reside in shallow marine waters Polyp and medusa body forms Specialized stinging cells (cnidocytes) Fluid-filled capsule, nematocyst Two-layered body sac Outer layer - Protective epidermis Inner layer - Gastrovascular cavity Nerve net found throughout body

Cnidarian Diversity

Hydra Freshwater cnidarian Small tubular poly body about one-quarter inch in length Gastrovascular cavity is central cavity Tentacles can respond to stimuli Can reproduce sexually and asexually

Anatomy of Hydra

A colony of polyps enclosed by a hard, chitinous covering. Chitin? Obelia A colony of polyps enclosed by a hard, chitinous covering. Chitin? Feeding polyps Extend beyond covering Have nematocyst-bearing tentacles Reproductive polyps Budding of new polyps Also has sexual reproduction (medusae) stage

Obelia Life Cycle

Ctenophora and Cnidarians Where are we now? How are cnidarians and ctenophora different from sponges? What new “feature” do they posses that sponges did not have? http://www.youtube.com/watch?v=bcmLxsJ5SAg&feature=related

Bilateral Symmetry New Characteristics Bilateral Symmetry animals have a “left and right” one plane of symmetry Cephalization identifiable or obvious “head” end of the animal having mouth and/or sensory organs at one end

Bilateral Symmetry Pseudocoelomates Both phyla today will be considered pseudocoelomates What is the difference between acoelomates, pseudocoelomates and coelomates (or eucoelomates?)

Bilateral Symmetry Coelomates (also known as eucoelomates — "true coelom") have a fluid filled body cavity called a coelom with a complete lining called peritoneum derived from mesoderm (one of the three primary tissue layers). Pseudocoelomate  have a pseudocoel (literally “false cavity”), which is a fully functional body cavity. Tissue derived from mesoderm only partly lines the fluid filled body cavity of these animals. Thus, although organs are held in place loosely, they are not as well organized as in a coelomate. Acoelomate animals, like flatworms, have no body cavity at all. Organs have direct contact with the epithelium. Semi-solid mesodermal tissues between the gut and body wall hold their organs in place.

Bilateral Symmetry Flatworms (phylum Platyhelminthes) Majority are parasitic Organ-level organization No specialized circulatory or respiratory structures Have undergone cephalization Ladder-type nervous system Ribbon worms (phylum Nemertea) Have distinctive proboscis Have a complete gut track

Belong to the phylum platyhelminthes. (Plat = flat) Flatworms Belong to the phylum platyhelminthes. (Plat = flat) There are three classes: Turbellaria Trematoda Cestoda

Characteristics of Flatworms They are acoelomates (they don’t have body cavities) They have bilateral symmetry Show cephalization Respiration through skin Single opening to digestive tract (pharynx)

Free-living Flatworms Planarians (genus Dugesia) Live in freshwater habitats Head is bluntly arrow shaped Auricles function as sense organs Two light-sensitive eye spots Three kinds of muscle layers: Outer circular layer Inner longitudinal layer Diagonal layer

Planarian Anatomy

Planarians Planarians, cont. Excretory organ functions in osmotic regulation and water excretion Can reproduce asexually Hermaphroditic Practice cross-fertilization

Parasitic flatworms are flukes (trematodes) and tapeworms (cestodes) Well-developed nerves and gastrovascular cavity are unnecessary Flukes Reproductive system well developed Usually hermaphroditic

Life Cycle of Schistosomiasis

Parasitic Flatworms Tapeworms Have anterior region with modifications for attachment to intestinal wall of host Behind head region, scolex, a long series of proglottids are found Segments each containing a full set of both male and female sex organs Complicated life cycles

Life Cycle of a Tapeworm, Taenia

Class Trematoda Are parasitic flukes Have suckers on both ends of the body Can live inside or outside of host Not much cephalization

Class Trematoda Nervous and excretory systems like turbellarians Hermaphrodites Have complex life cycles

Class Cestoda Parasitic Tapeworms Long, ribbon-like bodies Absorbs nutrients from host Hermaphrodites

Tapeworm Anatomy

Ribbon Worm, Lineus

Phylum Nemertea (Rhynchocoela) Ribbonworms The nemerteans (ribbon worms) are long, marine predatory worms and there are about 1000 species known. Unlike members of the Platyhelminthes nemerteans have a complete gut with a mouth and anus and a true circulatory system

Phylum Nemertea (Rhynchocoela) Ribbonworms Prey is captured using a long muscular proboscis armed with a barb called a stylet.. The proboscis lies in an interior cavity called the rhynchocoel and muscular pressure on fluid in the rhynchocoel causes the proboscis to be quickly everted. The prey is wrapped in the sticky, slime-covered, proboscis and stabbed repeatedly with the stylet. Neurotoxins in the slime incapacitate the prey.

8.18 Internal structure of female ribbon worm (left). Nemertean with proboscis extended (below) 8.18

Baseodiscus mexicanus a nemertean from 8.19 Baseodiscus mexicanus a nemertean from the Galapagos Islands

Pseudocoelom What is different about the animals we discussed today? How are flatworms (Platyhelminthes) different from cnidarians? How are nemertea (ribbon worms) different from flatworms?

Pseudocoelom Pseudocoelom: A “false” body cavity that is incompletely lined by mesoderm Provides a space for internal organs and can serve as hydrostatic skeleton Both phyla today are animals with a complete body gut track and pseudo coelom phylum Nematoda and Rotifera

Types of Body Cavities 3 types of body cavities

Types of Body Cavities acoelomate

Types of Body Cavities pseudocoelomate

Types of Body Cavities Coelomates – not there yet

Roundworms (phylum Nematoda) Pseudocoelom 59 Roundworms (phylum Nematoda) Non-segmented, generally colorless worms Several parasitic roundworms infect humans

Roundworm Anatomy

Parasitic Roundworms Ascaris – Intestinal roundworm Trachinella - Trichinosis Dirofilaria - Heartworms Wuchereria - Elephantiasis

Filarial Worm

Rotifers (phylum Rotifera) Named for crown of cilia resembling a rotating wheel Serves as both as an organ of locomotion and aids direction of food to mouth Important base of many ecosystems Planktonic Transparent organisms Can survive dessication

Rotifer

Rotifers on youtube.com 25X Magnification

Pseudocoelomates How are nematoda and rotifera different from platyhelminthes and nemertea (flatworms and ribbon worms?)