Download Chapter 29: Introduction to Invertebrates

Chapter 29: Introduction to Invertebrates
Evolution of Animals
Multicellularity
Sponges
True Tissues
Cnidarians and Comb Jellies
Hydra
Obelia
Bilateral Symmetry
Flatworms
Roundworms
Body Cavities
Acoelomates
Pseudocoelomates
Eucoelomates
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
Symmetry
Radial - Two identical halves
Bilateral - Definite right and left halves
Type of Coelom
Pseudocoelom
Coelom
Early Developmental Pattern
Protostome - First embryonic opening becomes the mouth
Deuterostome - Second embryonic opening becomes the mouth
Animals: Multicellular, Heterotrophic Eukaryotes
Traditional Phylogenetic Tree of Animals
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
1
Simple Sponge Anatomy
Note three types of cells:
Epidermal cells
Amoeboid cells (amoebocyte)
Collar cells (choanocyte)
Feed by taking water in through pores
Classified by spicule type (chalk, glass)
Have sponging – like collagen
True Tissue Layers
Total of three possible germ layers
Ectoderm
Endoderm, and
Mesoderm
phlya Ctenophora and Cnidaria develop only ectoderm and endoderm
Diploblasts
Radially symmetrical
Comb Jellies
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
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
Class Anthozoa: Sea anemones, corals
Class Hydrozoa: Hydra, Obelia, Physalia (Portuguese Man-of-War)
Class Scyphozoa: True jellyfish
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
Note cnidocyte with nematocyst
2
Obelia: A colony of polyps enclosed by a hard, chitinous covering
Feeding polyps
Extend beyond covering
Have nematocyst-bearing tentacles
Reproductive polyps
Budding of new polyps
Also has sexual reproduction (medusae) stage
Obelia Life Cycle
Note that the medusa form is the sexual part of the life cycle.
There are both feeding and reproductive polyps present in the colonial form
Bilateral Symmetry
Ribbon worms (phylum Nemertea)
Have distinctive proboscis
Flatworms (phylum Platyhelminthes)
Majority are parasitic
Organ-level organization
No specialized circulatory or respiratory structures
Have undergone cephalization
Ladder-type nervous system
Ribbon Worm, Lineus
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
Note well-developed cephalization and nervous system.
Both male and female sexual organs
Extended pharynx
Planarians
Excretory organ functions in osmotic regulation and water excretion
Can reproduce asexually
Hermaphroditic
Practice cross-fertilization
Parasitic Flatworms
Parasitic flatworms are flukes (trematodes) and tapeworms (cestodes)
Well-developed nerves and gastrovascular cavity are unnecessary
3
Flukes (tremetodes)
Reproductive system well developed
Usually hermaphroditic
Life Cycle of Schistosomiasis – blood fluke
Tapeworms (cestodes)
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
Pseudocoelom:
A “false” body cavity that is incompletely lined by mesoderm
Provides a space for internal organs and can serve as hydrostatic skeleton
Roundworms (phylum Nematoda)
Non-segmented, generally colorless worms
Several parasitic roundworms infect humans
Roundworm Anatomy
Parasitic Roundworms
Ascaris – Intestinal roundworm
Trichinella - Trichinosis
Dirofilaria - Heartworms
Wuchereria - Elephantiasis
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
Review: Evolution of Animals
Multicellularity
Sponges
True Tissues
Cnidarians and Comb Jellies
Hydra
Obelia
Bilateral Symmetry
Flatworms
Roundworms
Body Cavities
Acoelomates
Pseudocoelomates
Eucoelomates
4