Transcript Chapter 17

Chapter 17
The Evolution of Animals
What Is an Animal?
– Animals are:
•
•
•
•
Eukaryotic
Multicellular
Heterotrophic organisms that obtain nutrients by ingestion
Able to digest their food within their bodies
– Animal cells lack the cell walls that provide strong
support in the bodies of plants and fungi.
Sponges
No true tissues
Cnidarians
Radial symmetry
Ancestral
protist
Molluscs
Flatworms
Tissues
Annelids
Roundworms
Bilateral symmetry
Arthropods
Echinoderms
Chordates
Figure 17.5
– A second major evolutionary split is based on body
symmetry.
• Radial symmetry refers to animals that are identical all around a
central axis.
• Bilateral symmetry exists where there is only one way to split
the animal into equal halves.
Radial symmetry. Parts radiate from the center, so any slice
through the central axis divides into mirror images.
Bilateral symmetry. Only one slice can divide left and right
sides into mirror-image halves.
Figure 17.6
– Animals also vary according to the presence and type
of body cavity, a fluid-filled space separating the
digestive tract from the outer body wall.
– There are differences in how the body cavity forms.
• If the body cavity is not completely lined by tissue derived
from mesoderm, it is a pseudocoelom.
• A true coelom is completely lined by tissue derived from
mesoderm.
Body covering
(from ectoderm)
(a) No body cavity
Tissue-filled
region (from
mesoderm)
Digestive tract
(from endoderm)
Body covering
(from ectoderm)
(b) Pseudocoelom
Muscle
layer (from
mesoderm)
Pseudocoelom
Digestive tract
(from endoderm)
(c) True coelom
Coelom
Digestive tract
(from endoderm)
Body covering
(from ectoderm)
Tissue layer lining
coelom and
suspending
internal organs
(from mesoderm)
Figure 17.7
MAJOR INVERTEBRATE PHYLA
– Invertebrates:
• Are animals without backbones
• Represent 95% of the animal kingdom
Sponges
– Sponges include sessile animals that lack true tissues
and that were once believed to be plants.
Figure 17.8b
Cnidarians
– Cnidarians (phylum Cnidaria) are characterized by:
• The presence of body tissues
• Radial symmetry
• Tentacles with stinging cells
– The basic body plan of a cnidarian is a sac with a
gastrovascular cavity, a central digestive
compartment with only one opening.
– The body plan has two variations:
• The sessile polyp
• The floating medusa
– Cnidarians are carnivores that use tentacles, armed
with nematocysts (or cnidocytes) (“stinging cells”), to
capture prey.
Mouth/anus
Tentacle
Gastrovascular
cavity
Polyp form
Coral
Hydra
Sea anemone
Gastrovascular
cavity
Mouth/anus
Tentacle
Medusa form
Jelly
Figure 17.9
Tentacle
Coiled
thread
Capsule
Trigger
Discharge
of thread
Prey
Cnidocyte
Figure 17.10
Molluscs
– Molluscs (phylum Mollusca) are represented by softbodied animals, usually protected by a hard shell.
– Many molluscs feed by using a file-like organ called a
radula to scrape up food.
– The body of a mollusc has three main parts:
• A muscular foot used for movement
• A visceral mass housing most of the internal organs
• A mantle, which secretes the shell if present
Visceral mass
Coelom
Kidney
Heart
Mantle
Mantle
cavity
Reproductive
organs
Digestive
tract
Shell
Radula
Anus
Gill
Mouth
Foot
Digestive
tract
Radula
Nerve
cords
Mouth
Figure 17.11
– The three major groups of molluscs are:
• Gastropods, protected by a single, spiraled shell
Gastropods
Snail (spiraled shell)
Sea slug (no shell)
Figure 17.12a
• Bivalves, with a shell divided into two halves hinged together
Bivalves
(hinged shell)
Scallop
Figure 17.12b
• And cephalopods
– Typically lacking an external shell
– Built for speed and agility
Cephalopods
(large brain and tentacles)
Octopus
Squid
Figure 17.12c
MAJOR GROUPS OF MOLLUSCS
Gastropods
Bivalves
(hinged shell)
Cephalopods
(large brain and tentacles)
Snail (spiraled shell)
Scallop
Octopus
Squid
Sea slug (no shell)
Figure 17.12
Flatworms
– Flatworms (phylum Platyhelminthes) are the
simplest bilateral animals.
– Flatworms include forms that are:
• Parasites or
• Free-living in marine, freshwater, or damp habitats
Digestive tract
(gastrovascular
cavity)
Nerve cords
Mouth
Eyespots
(detect light)
Planarian
Nervous tissue
clusters
(simple brain)
Blood fluke
Bilateral symmetry
Reproductive unit
with skin removed
Head
Suckers
Tapeworm
Figure 17.13
Hooks
Annelids
– Annelids (phylum Annelida) have:
• Body segmentation, a subdivision of the body along its
length into a series of repeated parts
• A coelom
• A complete digestive tract with
– Two openings, a mouth and anus
– One-way movement of food
Anus
Brain
Main
heart
Coelom
Digestive
tract
Segment
walls
Mouth
Accessory
hearts
Nerve cord
Waste disposal organ
Blood vessels
Figure 17.15
– The three main groups of annelids are:
• Earthworms, which eat their way through soil
• Polychaetes, marine worms with segmental appendages
for movement and gas exchange
• Leeches, typically free-living carnivores but with some
bloodsucking forms
MAJOR GROUPS OF ANNELIDS
Earthworms
Polychaetes
Leeches
Giant Australian earthworm
Christmas tree worm
European freshwater leech
Figure 17.14
Roundworms
– Roundworms (phylum Nematoda) are:
• Cylindrical in shape, tapered at both ends
• The most diverse and widespread of all animals
– Roundworms (also called nematodes) are:
• Important decomposers
• Dangerous parasites in plants, humans, and other animals
(a) A free-living
roundworm
(b) Parasitic
roundworms in pork
(c) Canine heart
Infected with parasitic
roundworms
Figure 17.16
Arthropods
– Arthropods (phylum Arthropoda) are named for
their jointed appendages.
– There are about one million arthropod species
identified, mostly insects.
– Arthropods are a very diverse and successful group,
occurring in nearly all habitats in the biosphere.
– There are four main groups of arthropods.
MAJOR GROUPS OF ARTHROPODS
Arachnids
Crustaceans
Millipedes and Centipedes
Insects
Figure 17.17
General Characteristics of Arthropods
– Arthropods are segmented animals with specialized
segments and appendages for an efficient division of
labor among body regions.
– The body of arthropods is completely covered by an
exoskeleton, an external skeleton that provides:
• Protection
• Points of attachment for the muscles that move
appendages
Abdomen
Cephalothorax
(head and thorax)
Antenna
(sensory reception)
Eyes on
movable stalks
Mouthparts (feeding)
Walking leg
Swimming
appendage
Walking legs
Figure 17.18
Arachnids
– Arachnids:
• Live on land
• Usually have four pairs of walking legs and a specialized
pair of feeding appendages
• Include spiders, scorpions, ticks, and mites
Two feeding
appendages
Leg (four pairs)
Scorpion
Black widow spider
Dust mite
Wood tick
Figure 17.19
Crustaceans
– Crustaceans:
• Are nearly all aquatic
• Have multiple pairs of specialized appendages
• Include crabs, lobsters, crayfish, shrimps, and barnacles
Two feeding
appendages
Leg (three or more pairs)
Antennae
Crab
Pill bug
Shrimp
Crayfish
Barnacles
Figure 17.20
Millipedes and Centipedes
– Millipedes and centipedes have similar segments
over most of the body.
– Millipedes:
• Eat decaying plant matter
• Have two pairs of short legs per body segment
– Centipedes:
• Are terrestrial carnivores with poison claws
• Have one pair of short legs per body segment
One pair of legs per segment
Two pairs of legs
per segment
Millipede
Centipede
Figure 17.21
Insect Anatomy
– Insects typically have a three-part body:
• Head
• Thorax
• Abdomen
– The insect head usually bears:
• A pair of sensory antennae
• A pair of eyes
– The mouthparts are adapted for particular kinds of
eating.
– Flight is one key to the great success of insects.
Head Thorax
Abdomen
Antenna
Eye
Mouthparts
Figure 17.22
Insect Diversity
– Insects outnumber all other forms of life combined.
– Insects live in:
• Almost every terrestrial habitat
• Freshwater
• The air
Leaf roller
Banded Orange
Heliconian
Giraffe weevil
Yellow jacket wasp
Peacock katydid
Praying
mantis
Leaf beetle
Longhorn beetle
Figure 17.23
– Many insects undergo metamorphosis in their
development.
– Young insects may:
• Appear to be smaller forms of the adult or
• Change from a larval form to something much different as an
adult
The larva (caterpillar) spends
its time eating and growing,
molting as it grows.
Finally, the adult emerges
from the cocoon.
After several molts, the
larva becomes a pupa
encased in a cocoon.
Within the pupa, the larval organs break
down and adult organs develop from
cells that were dormant in the larva.
The butterfly flies off and reproduces, nourished mainly
by calories stored when it was a caterpillar.
Figure 17.24-5
Monarch butterflies
Figure 17.24a
Echinoderms
– Echinoderms (phylum Echinodermata):
• Lack body segments
• Typically show radial symmetry as adults but bilateral
symmetry as larvae
• Have an endoskeleton
• Have a water vascular system that facilitates movement
and gas exchange
– Echinoderms are a very diverse group.
Sea star
Tube feet
Sea urchin
Sea cucumber
Sand dollar
Figure 17.25