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CHAPTER 30: ANIMALS: PART I
LECTURE OUTLINE
30.1 Evolutionary Trends Among Animals
Animals are extremely diverse, but in general they are heterotrophic, typically have the power of
movement or locomotion by means of muscle fibers, are multicellular, have a life cycle in which
the adult is typically diploid, and undergo sexual reproduction and produce an embryo that goes
through development stages. All but one of the 30 animal phyla is invertebrates. Only one
phylum contains vertebrates.
Level of Organization
Three levels of organization exist in the animal kingdom: the cellular, tissue, and organ
levels.
Type of Body Plan
Two body plans are observed in the animal kingdom: the sac plan and the tube-within-atube plan.
Type of Symmetry
Animals can be asymmetrical, radially symmetrical, or bilaterally symmetrical.
Type of Body Cavity
The body cavity that contains internal organs is often called a coelom. Animals can be
acoelomate, have a pseudocoelom, or have a true coelom.
Segmentation
Segmentation is the repetition of body parts along the length of the body. Animals can be
nonsegmented or segmented.
Jointed Appendages
In arthropods, jointed appendages provide a means of locomotion.
30.2 Introducing the Invertebrates
Sponges: Multicellular
Sponges are aquatic. They are multicellular but lack organized tissues. They are filter
feeders. Sponges can reproduce both asexually and sexually.
Cnidarians: True Tissues
Cnidarians are multicellular, tubular, or bell-shaped animals that reside mainly in shallow
coastal waters. They are radially symmetrical. Examples include sea anemone, cup
coral, Portuguese man-of-war, and jellyfish. They have specialized stinging cells called
cnidocytes.
Hydra
Hydra is a freshwater cnidarian. It has a sac body plan. It has two tissue layers:
ectoderm and endoderm.
Flatworms: Bilateral Symmetry
Flatworms have bilateral symmetry. They also have three germ layers. They are
acoelomates.
Planarians
Freshwater planarians are small, literally flat, worms. They have an excretory
and a nervous system.
Parasitic Flatworms
The parasitic flatworms include the tapeworms and the flukes.
Tapeworms
Tapeworms are endoparasites of various vertebrates, including humans.
They attach to the intestinal wall of the host and feed.
Flukes
Flukes are all endoparasites of various vertebrates. They are usually
named for the type of vertebrate organ they inhabit.
Roundworms: Pseudocoelomates
Roundworms have a tube-within-a-tube body plan and a body cavity. The body cavity is
a pseudocoelom. They have a hydrostatic skeleton and are nonsegmented.
Ascaris
A female Ascaris is very reproductively prolific. They are most commonly
parasites of humans and pigs.
Other Roundworms
Trichinosis is a fairly serious infection cause by eating pork that is not fully
cooked that contains encysted larvae of the round worm Trichinella spiralis.
Elephantiasis is caused by a roundworm called the filarial worm. Pinworm and
hookworm infections are more common in the United States.
30.3 Molluscs: Coelomates
The mollusks and all the other species we will study are coelomates. They have bilateral
symmetry, three germ layers, the organ level of organization, and a tube-within-a-tube body plan.
Unique Characteristics of Molluscs
All molluscs have a body composed of at least three parts: the visceral mass, the foot, and
the mantle.
Gastropods
Gastropods include nudibranchs, conchs, and snails. The foot is ventrally
flattened.
Cephalopods
Cephalopods include octopuses, squid, and nautiluses. The foot has evolved into
tentacles about the head.
Bivalves
Bivalves include clams, mussels, oysters, and scallops. Their shells have two
parts.
The Visceral Mass
The clam has an open circulatory system and a heart. It also has a
nervous system and a digestive system.
Comparison
Refer to Table 30.2 for a comparison of a clam, squid, and land snail.
30.4 Annelids: Segmented Worms
Annelids are segmented. Internally, the segments are partitioned by septa. They have a
hydroskeleton, a closed circulatory system, a ventral solid nerve cord, and nephridium.
Polychaetes
Most annelids are marine organisms. They have many setae or bristles that anchor the
worm or help it move.
Oligochaetes
The oligochaetes, which include earthworms, have few setae per segment.
Segmentation
Segmentation is evidenced by body rings, coelom divided by septa, setae on most
segments, ganglia and lateral nerves in each segment, nephridia in most segments, and
branch blood vessels in each segment.
Reproduction
Earthworms are hermaphroditic.
Comparison with Clam Worm
The comparison of the marine clam worm with the terrestrial earthworm highlights the
manner in which earthworms are adapted to life on land.
Leeches
Leeches have no setae and each body ring has several transverse grooves. Among their
modifications are two suckers.
30.5 Arthropods: Jointed Appendages
Arthropods are extremely diverse. Over one million species have been discovered and described.
Arthropods have jointed appendages and an exoskeleton made of chitin. They are segmented and
have a well-developed nervous system that includes a brain and a ventral solid nerve cord.
Crustaceans
Crustaceans include barnacles, shrimps, lobsters, and crabs. They are named for their
hard shells.
Internal Organs
In the crayfish, the digestive system includes a stomach. The coelom is reduced
to a space around the reproductive system. They have an open circulatory
system. The nervous system is very similar to that of an earthworm.
Insects
Insects are very numerous and diverse. Insects have a body that is divided into a head, a
thorax, and an abdomen. The head bears sensory antennae, a pair of compound eyes, and
several simple eyes. The mouthparts are adapted for the type of food. Wings may be
present.
Internal Organs
In the grasshopper, there is an excretory system, a respiratory system, and a
circulatory system.
Reproduction and Development
Metamorphosis is a change in form and physiology that occurs as an immature
stage, called a larva, becomes an adult.
Comparison with Crayfish
A comparison of a grasshopper with a crayfish reveals the adaptations to a
terrestrial environment.
Arachnids
The arachnids include scorpions, spiders, ticks, and mites. They have six pairs of
appendages.