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Chapter 23 : Learning Goals

. What Are the Key Features of ? . Which Anatomical Features Mark Branch Points on the Evolutionary Tree? . What Are the Major Animal Phyla? . You should be able to match the common name to the Phyla and explain it’s impact on humans What Are the Key Features of Animals?

. Animals possess all of the following characteristics – Multicellularity – Their cells lack a cell wall – They obtain energy by consuming other organisms – Most reproduce sexually – They are motile at some point in the life cycle – They are able to respond rapidly to external stimuli Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? . Most animal phyla that currently populate Earth were present by the Cambrian period (544 million years ago) – The scarcity of pre-Cambrian fossils led systematists to search for clues about the evolutionary history of animals by examining features of: –Anatomy –Embryological development –DNA sequences 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? . Certain features represent evolutionary milestones, and mark major branching points on the animal evolutionary tree – The appearance of tissues – The appearance of body symmetry – and development An Evolutionary Tree of Some Major Animal Phyla

Fig. 23-1 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? . Lack of tissues separates sponges from all other animals – Tissues are groups of similar cells that carry out a specific function (e.g., muscle) – Sponges are the only modern-day animals that lack tissues Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? . Animals with tissues exhibit either radial or bilateral symmetry – Symmetrical animals have an upper (dorsal) surface and a lower (ventral) surface – Symmetrical animals are divided into two groups: –Animals that exhibit radial symmetry –Animals that exhibit bilateral symmetry Body Symmetry and Cephalization

central axis

anterior plane of symmetry

plane of symmetry

posterior

(a) Radial symmetry (b) Bilateral symmetry

Fig. 23-2 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? . Animals with radial symmetry can be divided into roughly equal halves by any plane that passes through the central axis – Animals with radial symmetry have two embryonic tissue (germ) layers – , which is an outer layer that covers the body, lines its inner cavities, and forms the nervous system – , which is an inner layer that lines most hollow organs – Bilaterally symmetrical animals have three embryonic tissue (germ) layers – A layer of between the ectoderm and endoderm 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? . Bilaterally symmetrical animals have heads – Animals with bilateral symmetry can be divided into mirror-image halves only along one plane that runs down the midline – These animals exhibit cephalization, the concentration of sensory organs and a brain in a well-defined head, with definite anterior (head) and posterior regions Body Symmetry and Cephalization

central axis

anterior plane of symmetry

plane of symmetry

posterior

(a) Radial symmetry (b) Bilateral symmetry

Fig. 23-2 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? . Most bilateral animals have body cavities – Body cavities are fluid-filled cavities between the digestive tube and the outer body wall 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? . structure varies among phyla – The most common body cavity is a , a fluid-filled body cavity that is completely lined with mesoderm –Phyla with animals that have this type of body cavity are called coelomates, and include , , mollusks, , and (which include humans) Body Cavities

The body cavity is The body cavity is partially, There is no cavity completely lined with tissue but not completely, lined with between the body wall derived from mesoderm tissue derived from mesoderm and digestive tract

body wall body wall

coelom pseudocoelom body wall

digestive digestive digestive tract tract tract

digestive digestive digestive cavity cavity cavity

(a) “True” coelom (b) “False” or pseudocoelom (c) No coelom (annelids, chordates) (roundworms) (cnidarians, )

Fig. 23-3 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? – A body cavity that is not completely surrounded by mesoderm is known as a pseudocoelom –Phyla with animals that have this type of body cavity are called pseudocoelomates and include roundworms, such as Body Cavities

The body cavity is The body cavity is partially, There is no cavity completely lined with tissue but not completely, lined with between the body wall derived from mesoderm tissue derived from mesoderm and digestive tract

body wall body wall

coelom pseudocoelom body wall

digestive digestive digestive tract tract tract

digestive digestive digestive cavity cavity cavity

(a) “True” coelom (b) “False” or pseudocoelom (c) No coelom (annelids, chordates) (roundworms) (cnidarians, flatworms)

Fig. 23-3 23.2 Which Anatomical Features Mark Branch Points on the Animal Evolutionary Tree? . Bilateral organisms develop in one of two ways based on embryological development – Protostome development – In these animals, the body cavity forms within the space between the body wall and the digestive cavity – These animals include nematodes, arthropods, annelids, and mollusks – Deuterostome development – In these animals, the body cavity forms as an outgrowth of the digestive cavity – Echinoderms and chordates are

Protostomes Blastopore forms mouth first

Deuterostomes Blastopore forms first

• Molecular sequences 23.3 What Are the Major Animal Phyla?

. Sponges have a simple body plan – Sponges belong to the Porifera and are found in most marine and aquatic environments –Sponges do not move, but occur in a variety of sizes and shapes –They may reproduce asexually by budding, where the adult produces miniature versions of itself that drop off and assume an independent existence –They may reproduce sexually through fusion of sperm and eggs An Evolutionary Tree of Some Major Animal Phyla

Fig. 23-1 The Diversity of Sponges

Fig. 23-4 23.3 What Are the Major Animal Phyla?

. Some sponges contain chemicals useful to humans – A number of chemicals within sponges have proved to be valuable medicines –The drug spongistatin is an emerging treatment for the fungal infections that sicken AIDS patients –Some medicines derived from sponges include some promising new cancer drugs 23.3 What Are the Major Animal Phyla?

. Sponges lack true tissues and organs – The sponge body is perforated by tiny pores through which water passes, and by fewer, large openings through which water is expelled – As water passes through the sponge, oxygen is extracted, and microorganisms are filtered out and digested by individual cells The Body Plan of Sponges (water flow out of the sponge)

epithelial cell pore

spicules (water flow into the sponge) amoeboid cell

pore cell

collar cell

(water flow)

Fig. 23-5 – Sea Anemone

. Radial symmetry . Two tissue layers . Filled with water . Nematocysts - stinging organelles that release toxins 23.3 What Are the Major Animal Phyla?

. Cnidarians are well-armed predators – Sea jellies, sea anemones, corals, and hydrozoans belong to the phylum Cnidaria – These animals are mostly marine and are all carnivorous predators – The cells of cnidarians are arranged into distinct tissues, including a contractile muscle-like tissue and an organized nerve net An Evolutionary Tree of Some Major Animal Phyla

Fig. 23-1 Cnidarian Diversity

Fig. 23-6 Echinoderms -

. Endoskeleton . Coelom (cavity lined with tissue)forms from gut tube tissue . Deuterostomes . . Tube feet (locomotion) 23.3 What Are the Major Animal Phyla?

. Echinoderms have a calcium carbonate . The phylum Echinodermata includes sand dollars, sea urchins, sea stars, sea cucumbers, and sea lilies – larvae exhibit bilateral symmetry; adults show radial symmetry The Diversity of Echinoderms

Fig. 23-27 Platyhelminthes - flatworms

. Bilateral symmetry . 3 tissue layers . Cephalization (nerve mass) . True organs and systems . Aceolomate (no body cavity) . Parasitic forms 23.3 What Are the Major Animal Phyla?

. Some flatworms are harmful to humans – Tapeworms can infect people who eat improperly cooked beef, pork, or that has been infected by the worms –Tapeworm larvae form encapsulated resting structures, called cysts, in the muscles of these animals –The cysts hatch in the human digestive tract, and the young tapeworms attach themselves to the lining of the intestine 23.3 What Are the Major Animal Phyla?

. Some flatworms are harmful to humans (continued) –Tapeworms may grow to a length of more than 20 feet (7 meters), absorbing nutrients across their outer surface –They release eggs that are shed in the hosts feces, continuing the infective cycle The Life Cycle of the Human Pork Tapeworm

1 A human eats poorly cooked pork with live cysts 2 A larval tapeworm is liberated by digestion and attaches to the human’s adult tapeworm head (attachment site) intestine 6 inches

3 The tapeworm matures in a human intestine, producing a series of reproductive segments; each segment contains both male and female sex organs

8 The larvae form cysts in pig muscle

4 Eggs are shed from the posterior end of the worm and are passed with human feces

5 A pig eats food contaminated by infected feces

7 The larvae migrate through 6 Larvae hatch in the pig’s intestine blood vessels to pig muscle Fig. 23-10 Annelida - segmented worms

. Segmented body . Bilateral symmetry . 3 tissue layers . Ceolom (fully enclosed body cavity) . Organ systems are more fully developed . and Leaches . Decomposers and Parasites Diverse Annelids

Fig. 23-12 Nematoda - round worms

. Exoskeleton (molts) . Unsegmented . Psuedocoelom (false body cavity) . Bilateral worms . 3 tissue layers . Parasites and decomposers Diseases caused by Nematodes Diseases caused by Nematodes

. Dracunculus medinensis: The Guinea Worm . Phylum Nematoda . West Africa, East Africa, India

Guinea Worm Life Cycle

Vector

Cyclops – a freshwater crustacean

Host—human drinking contaminated water. Guinea worm larvae are freed from Cyclops in human gut. Guinea Worm Life Cycle

Female worm migrates to lower extremities to release her eggs into water.

After releasing eggs, female dies inside host. (clams, snails, slugs, & )

• unsegmented • exhibit bilateral symmetry • protostome coelomates • aquatic & terrestrial • possess all organ systems The Diversity of Bivalve Mollusks

Fig. 23-15 The Diversity of Cephalopod Mollusks

Fig. 23-16 Mollusks – soft-bodied

. Soft body . Radula (scrapes) . Muscular foot . Protostome ceolomates . Bilateral symmetry . Possess all organ systems Arthropods

. Earth’s largest phylum Arthropods

. Earth’s largest phylum . Includes , mites, ticks, scorpions, centipedes, millipedes, lobsters, crabs, beetles, and other insects. Arthropods

. Earth’s largest phylum . Characterisitics: – External skeleton – Specialized body segments – Jointed appendages

Arthropods

. Specialized segments – Head – Thorax – Abdomen

Arthropods

. Organ systems – Efficient respiratory system including tracheae – Most have antennae to detect movement, sound or chemicals – Some have compound eyes capable of color vision Major Classes

. Centipides . Millipedes 23.3 What Are the Major Animal Phyla?

. Myriapods have many legs – The myriapods include the centipedes and millipedes –They have one pair of antennae –They have simple light-detecting eyes –They respire by means of tracheae – Centipedes have one pair of legs per body segment – Millipedes have two pairs of legs per body segment Major Arthropod Classes

. Crustaceans

Major Arthropod Classes

. Arachnids (spiders, ticks, scorpions)