Chapter 23 Invertebrate Diversity

1. Chapter 23Invertebrate Diversity Section 1 – Diverse animals share several key characteristics Section 2 – Sponges are relatively simple animals with porous bodies Section 3 – Cnidarians are radial animals with stinging cells Section 4 – Flatworms are the simplest bilateral animals Section 5 – Roundworms and rotifers have complete digestive tracts Section 6 – Annelida are segmented worms Section 7 – Mollusks show diverse variations on a common body form Section 8 – Echinoderms have spiny skin and a water vascular system Section 9 – Animal diversity “exploded” during the Cambrian period

2. The Body of a Flatworm • Flatworms (phylum Platyhelminthes) are bilaterally symmetrical. • Definition: member of a group of small, leaflike or ribbonlike invertebrates that includes planarians • Definition: body plan in which an animal can be divided into two equal sides • Flatworms have mirror-image left and right sides, a distinct head (anterior end), a distinct tail (posterior end), a back side (dorsal), a bottom side (ventral), and two side surfaces (lateral). • Flatworms are the simplest animals to have three tissue layers: the ectoderm, mesoderm, and endoderm.

3. During an animal’s early development: • THE ECTODERM: develops into the body covering. • THE MESODERM: develops into an internal tissue-filled region. • THE ENDODERM: develops into the digestive sac. • Similar to cnidarians, flatworms have a digestive cavity – food enters and wastes exit from one opening located on the ventral surface. • When the animal is feeding, a muscular tube projects through the mouth and sucks in food.

4. Flatworms can move in several ways: • They use cilia on its ventral surface to slide about in search for food. • They have muscles that enable it to twist and turn. • Flatworms are aware of their surroundings by: • the pair of eyespots that detect light. • the side flaps that function mainly for smell. The Diversity of Flatworms • The 20,000 known species are divided into three classes: • Class Turbellaria: mostly free-living and marine (planarians) • Class Trematoda: parasites that absorb nutrients from the body fluids of a living host (blood fluke) • Class Cestoidea: parasites that live in the digestive tracts of vertebrates (tapeworms)

5. Chapter 23Invertebrate Diversity Section 1 – Diverse animals share several key characteristics Section 2 – Sponges are relatively simple animals with porous bodies Section 3 – Cnidarians are radial animals with stinging cells Section 4 – Flatworms are the simplest bilateral animals Section 5 – Roundworms and rotifers have complete digestive tracts Section 6 – Annelida are segmented worms Section 7 – Mollusks show diverse variations on a common body form Section 8 – Echinoderms have spiny skin and a water vascular system Section 9 – Animal diversity “exploded” during the Cambrian period

6. The Body of a Roundworm • Most roundworms, or nematodes (phylum Nematoda), range in length from less than 1 mm to more than 7 meters. • Definition: member of a group of cylindrical invertebrates with pointed heads and tapered tails • The largest roundworms are parasites found in whales. • Like flatworms, roundworms have three tissue layers. • One characteristic that makes roundworms (and annelids) different from flatworms (and cnidarians) is the presence of a complete digestive tract. • Definition: continuous digestive tube with a separate mouth and anus

7. In animals with a digestive tract, the anterior region of the tract churns and mixes food with enzymes for digestion – the posterior region absorbs nutrients from the digested food and disposes of wastes. The Diversity of Roundworms • Roundworms are among the most numerous on Earth, totaling about 15,000 known species.

8. Roundworms live almost every place there is rotting organic matter and play a roles as important decomposers on the bottom of lakes and oceans. • Other roundworms thrive as parasites in the moist tissues of plants and in the body fluids and tissues of animals. • Free-living roundworms (non-parasitic) roundworms are the most abundant. • Many species of parasitic roundworms attack the roots of plants and tissues of animals – humans can be hosts to at least 50 species of roundworms parasites. • One disease that can affect humans is called trichinosis humans acquire this disease by eating undercooked pork or other meat that is infected with worms. • Roundworm parasites of animals are known by several common names such as hookworm, pinworm, and threadworm (names based on worm’s appearance).

9. Chapter 23Invertebrate Diversity Section 1 – Diverse animals share several key characteristics Section 2 – Sponges are relatively simple animals with porous bodies Section 3 – Cnidarians are radial animals with stinging cells Section 4 – Flatworms are the simplest bilateral animals Section 5 – Roundworms and rotifers have complete digestive tracts Section 6 – Annelida are segmented worms Section 7 – Mollusks show diverse variations on a common body form Section 8 – Echinoderms have spiny skin and a water vascular system Section 9 – Animal diversity “exploded” during the Cambrian period

10. The Body of an Annelid • Earthworms and other segmented worms (phylum annelida) are called annelids. • Definition: segmented worm • Annelida “little rings” • Segmentation is an advantage because each segment has its own muscles, allowing shortening and lengthening of the body for movement. • Within each segment is a dense cluster of nerve cells and waste-excreting organs. • Annelids have a distinct head and tail and it’s body segments are all very similar. • The digestive tract is not segmented and runs the length of the animal, along with the nerve cord and two main blood vessels.

11. FIGURE 23-12 • Annelids have a closed circulatory system. • Definition: blood transport system in which blood remains enclosed in vessels; nutrients, oxygen, and wastes diffuse through vessel walls • On the underside of a segmented worm are bristles – these bristles aid in movement. FIGURE 23-15

12. Annelids are bilaterally symmetrical and have three tissue layers. • Bilateral symmetry  when divided in half, it is identical on both sides (mirror image) • The tissue layers are organized differently in each of the three groups of worms. • FLATWORMS are examples of acoelomates. • Definition: animal lacking a body cavity • ROUNDWORMSeachhave a pseudocoelom. • Definition: fluid-filled internal space that is in direct contact with the wall of the digestive tract • ANNELIDS each have a coelom. • Definition: fluid-filled body cavity completely lined by a layer of mesoderm cells

13. The Habitat of Annelids • Segmented worms live in the soil, fresh water, and the sea – everywhere except frozen soil and dry sand. • The soil is the worms main source of oxygen – it diffuses into the earthworm through the skin. • DURING THE DAY: The cool, moist soil provides protection for the worm. • AT NIGHT: They come to the surface and stay close to their burrows. The Reproduction of Annelids • Segmented worms are hermaphrodites (bodies contain male and female sex organs). • During mating, two worms exchange sperm the sperm fertilizes the eggs contained in the bodies of each worm the fertilized eggs are expelled in the soil  two-three weeks later, worms hatch from the eggs.

14. The Diversity of Annelids • There are about 15,000 known species of annelids, grouped into three classes. • Class Polychaeta:includes species that scavenge for food on the ocean floor (sandworms) • Class Oligochaeta:includes species who tunnel through the soil helping air to circulate in it (earthworms) • Class Hirudinea:includes parasitic leeches