BioScience 102 - Lower Invertebrates

I. Introduction

A. Kingdom Animalia - the Animals

1. Multicellular, aerobic heterotrophs

2. Nutrition from large molecules

a. Ingestion - eating whole or in parts

b. Parasitism - close relationship where parasite obtains nutrition from living host

3. Bodies are diploid - only the gametes are haploid

4. Most animals are motile - move around as a result of their own activity

a. Some sessile - not motile and attached

b. Sessile forms--mechanisms for dispersal - just like plants and fungi

B Invertebrates = animals without backbones

C. A group with great diversity

1. Many phyla

2. Possibly a result of multiple lines of evolution from the Protista

a. Fossil evidence from 800 million years in the form of tracks and burrows in marine sediments

b. Ciliates--multiple nuclei, then compartments

c. Colonial flagellates with specialized cells

D. Body symmetry

1. Asymmetrical - no specific or characteristic shape

2. Radial - parts arranged around a central axis

a. Through the central axis in many planes and numerous equal halves

b. Usually associated with sessile or very slow moving animals

c. Always animals that live in water

3. Bilateral symmetry

a. Two sides that are mirror images of each other (not perfect)

b. Two ends - anterior and posterior

c. Usually a "top and bottom" = the dorsal and ventral

d. Evolutionary trend toward cephalization - a concentration of the sensory and nervous control areas in the head (anterior) end which leads into the environment

II. Placozoan - plate animal

A. Soft bodied and flat and a bit lumpy "like pita bread"

B. Cells arranged in two layers

C. Specialized cells migrate.

1. Lower layer with glandular cells which secrete enzymes for digestion

2. What kingdom studied earlier with same manner?

D. Reproduction--unknown

F. One known organism - Trichoplax adhaerens

III. Porifera - the sponges

A. mostly marine, a few are freshwater

B. Usually asymmetrical

1. Outer layer of a flattened epidermis

2. Inner layer of choanocytes - collar cells

3. Non-cellular layer between which contains

a. amoeboid cells - wandering cells

b. protein fibers

c. spicules - needles of calcium carbonate or silica

C. Two layered body around one or more cavities

1. body wall is perforated

2. beating flagella create current of water into the cavity

3. food coming in with water is trapped on the collar of the choanocytes

D. Reproduction

1. Sexual with eggs and sperm

2. Asexual by fragmentation (passive) or by production of gemmules (protected groups of cells)

IV. Cnidarians (tissue level) jellyfish, sea anemones, corals

A. Radial symmetry

B. Body Plan

1. Two cell layers

a. outer epithelium - epidermis

b. inner epithelium with digestive cells = the gastrodermis

2. Mesoglea - a thick proteinaceous separating layer

C. Specialized cells of the tissues - a group of one type of cell--a particular function

1. Neurons (but, not nerve cells)

2. muscle cells

3. secretory cells

4. cnidoblast cells that produce by secretion the nematocysts

D. Body forms

1. Polyp

a. column like with ring of tentacles

b. central body cavity

c. sometimes with an external skeleton

d. sessile

2. Medusa - jellyfish

a. bell-shaped with ring of tentacles

b. central sack-like digestive area

c. swims by contracting the bell rapidly

E. Life Cycle

1. Medusa is sexual stage producing gametes

2. Fertilization produces a zygote which develops into a planula larva

3. Settles and undergoes metamorphosis into a polyp

4. Variations

a. medusa only

b. polyp or polyps only (hydroids, sea anemones and corals

V. Platyhelminthes - the flatworms

A. Bilateral symmetry

B. Three cell layers

1. Ectoderm

2. Mesoderm

3. Endoderm

C. Simple organs - groups of one or more kinds of tissues arranged to perform a specific function

D. Simple organ systems - group of organs that perform a specific function

1. Digestive

2. Excretory

E. Reproduction

A. Sexual - are often Hermaphrodites

B. Asexual by fission

F. Classes

1. Turbellarians are free living in fresh and salt water and occasionally in moist terrestrial conditions

2. Flukes

a. parasites

b. complex life cycles of at least two hosts - one invertebrate and one vertebrate (often humans)

3. Tapeworms

a. segmented

b. usually are intestinal

c. multiple host life cycles

VI. Nematoda - roundworms (nema = “thread”)

A. Body cavity within the mesoderm around the digestive system

1. Looks like a coelom

2. Specifically a pseudocoelom

B. Digestive system with two openings

C. Hydrostatic skeleton

D. Parasitic and free living

E. Reproduction

1. Sexual only

2. Cell constancy (total number of body)

VII. Rotifera - wheel animals

A. Jointed bodies

B. Pseudocoelom

C. complex organ systems

D. Sexual reproduction

1. Males and females

2. Parthenogenesis

a. female populations

b. males only when "needed"

WADSWORTH - CD

Porifera

5879

5884

5885 - 5892

5899

Cnidaria

5912 - 5944

Platyhelminthes

5951 - 5958

7039 - 7040 Flukes

7053 - 7065

Nematoda

7027

Rotifera

7068