Chapter 23
The Animal Kingdom
General Features of Animals
• All animals are multicellular heterotrophs
• They are diverse in form
– Invertebrates are animal species that lack a
backbone
– Vertebrates have a backbone (about 1% of
Kingdom Animalia)
•
•
•
•
No cell walls
Active Movement
Sexual Reproduction
Embryonic Development
Evolution
• The first
multicellular
animals
evolved about
600 million
years ago.
• From humble
beginnings,
they diversified
into many
habitats.
Evolutionary
Innovations
• We will learn about
animal diversity by
examining a series
of nine key
evolutionary
innovations, each
exemplified by a
major phylum.
The Simplest Animals
• The simplest animals,
members of the phylum
Porifera
• Members of phylum
Porifera include
sponges
• Characteristics of
sponges
– Lack symmetry
– Not organized into
tissues
Sponges
• Sponges are perforated by tiny holes (where
name of phylum comes from
• They have unique flagellated cells that line the
body cavity of the sponge
• The flagella on the cells will draw water
through the sponge and throughout the body
cavity
• Any food particles in the water will be trapped
and later ingested
Phylum Cnidaria
• Phylum Cnidaria consists of jellyfish, sea anemones, sea coral
and hyroids
• Unlike sponges, they have symmetry and tissues
• Able to undergo extracellular digestion, where digestion takes
place inside a body cavity
• Cnidarians have two true tissue layers: ectoderm and
endoderm
• They have radial symmetry and a nerve net to provide sensory
input.
Symmetry
• Symmetrical objects have similar parts that are
arranged in a similar manner
• Three types of symmetry
– Asymmetry – no pattern in parts
– Radial Symmetry – when a body is constructed around
a central axis
– Bilateral symmetry – is when an animal is constructed
with equivalent parts on both sides of a plane,
includes a definite head end, known as cephalization
Phylum Platyhelminthes
• In phylum Platyhelminthes (flatworms), they have
bilateral symmetry, so they have cephalization
• Also have three embryonic layers, the outer ectoderm,
the inner endoderm, and a third layer, the mesoderm,
which forms between the ectoderm and the endoderm
– The ectoderm forms into the outer covering of the body
and the nervous system
– The digestive and intestines develop from the endoderm
– The skeleton and muscle form from the mesoderm
• They do not have a body cavity, making them
acoelomates
Flatworms
• Have a simple body design, but do have a definite
head and organs
• Most species are parasitic, occurring within the
bodies of many other kinds of animals
• Have an incomplete gut, with only one opening
– They cannot feed, digest, and eliminate waste
simultaneously
• Lack a circulatory system
– Undergo diffusion of oxygen
• Many are hermaphroditic, with each individual
containing both male and female parts
Body Cavity
• A key transition in the evolution of the animal
body was that of a body cavity.
– All bilaterally symmetrical animals other than solid
worms have a cavity within their body
• Important for body design for:
– Circulation – fluids can move within the body cavity,
permitting the rapid passage of materials from one
part of body to another
– Movement – Fluid in cavity makes animal’s body rigid,
making it harder for muscle contractions
– Organ Function – Body organs can function without
body being deformed by surrounding muscles
Body Cavities
• Three basic kinds of body
plans found in bilaterally
symmetrical animals
– Acoelomates – have no body
cavity
– Pseudocoelomates – have a
body cavity called the
pseudocoel located between
the mesoderm and endoderm
develops entirely
– Coelomates – has a fluid-filled
body cavity not between the
endoderm and mesoderm, but
rather entirely within the
mesoderm, coelom
• Gut is suspended, along with
other organ systems
Phylum Nematoda
• In phylum Nematoda, they are pseudocoelomates, the
first evolutionary phylum to have an internal body
cavity.
– Includes nematodes, ellworms and rotifers
• Nematodes mouth is often equipped with piercing
organs, and the food will pass through the mouth as a
result of the sucking action of a muscular chamber,
known as the pharynx. After passing the pharynx food
continues through the digestive tract and is eliminated
through the anus
Phylum Mollusca
• Phylum Mollusca have a coelom, which is more
functional than animals without coeloms.
– This is because of primary induction, where one of the
three primary tissues (endoderm, mesoderm, and
ectoderm) interact with one another
• Only coelomate without a segmented body
• Most have a radula, a rasping, tongue-like organ
– Used to scrape algae off rocks
Phylum Mollusca
• Mollusks are divided into with outwardly
different body plans
• The three different classes of mollusks
– Gastropods – include snails and slugs, use a muscular
foot to crawl, their mantle secretes a single, hard
protective shell
– Bivalves – include clams, oysters and scallops, secrete
a two-part shell, with a hinge
– Cephalopods – include octopuses and squids, have a
modified mantle cavity to create a jet propulsion
system to propel them through water
Phylum Annelida
• In this phylum, their key evolutionary trait is
segmentation, where the building of a body is
from a series of similar segments
• Includes: Earthworms, brittle worms
• In phylum Annelida, there segmentation are
nearly identical segments
– The advantage of segmentation is hat segments
are able to have different functions, such as
reproduction, feeding
Phylum Annelida
•
Annelida organization is simply basic body
structure of Annelida: is a tube within a
tube; the digestive tract is a tube suspended
within the coelom
1. Repeated segments: each segment has
digestive, excretory, and locomotor organs
2. Specialized segments: sensory organs that are
sensitive to light
3. Connections: circulatory and nervous
connections to each segment
Phylum Arthropoda
• This phylum includes insects, crabs, shrimp
lobsters, crayfish, water fleas
• Their evolutionary adaption include jointed
appendages and exoskeleton
• Their exoskeleton is a rigid external skeleton
made of chitin and provides places for muscle
attachment
– Helps protect against predators and slow water
loss
Phylum Arthropoda
• Arthropods that lack jaws, also known as
mandibles are called chelicerates.
– These include spiders, mites, scorpions
• Those with mandibles that were formed
through the modification of anterior
appendages are known as mandibulates.
– This group includes crustaceans, insects,
centipedes and millipedes
Mandibulates
• Crustaceans – large, diverse group of primary aquatic animals.
– Most have two pair of antennae, three pairs of chewing
appendages, and various number of legs
– Have compound eyes
• Millipedes and Centipedes
– Centipedes have one pair of legs on each segment
– Millipedes have two pairs of legs on each segment
Mandibulates
• Insects are the largest group of arthropods
• They have three body sections
– Head – very elaborate, with one pair of antennae
and elaborate mouthparts and compound eyes
– Thorax – has three segments as well, each of
which have one pair of legs; most insects have two
pairs of wings attached to the thorax
– Abdomen – digestion takes place, and have
excretion organ called Malpighian tubes
Embryonic Development
• In coelomates, there are two different types of
embryonic development
• In mollusks, annelids, and arthropods, the
mouth near the blastopore making it a
protostome
• Protostomes form in a cleave radially and are
tightly packed
Embryonic Development
• In echinoderms and chordates,the anus forms
near the blastopore, making it a deuterostome
• It forms through spiral cleavage
Phylum Echinodermata
• In phylum Echinodermata include sea stars, sea
urchins, sand dollars and sea cucumbers
• Their key evolutionary developments include
deuterostome development and endoskeleton
• The endoskeleton is composed of hard calcium-rich
plates just beneath a delicate skin
• They have pentamerous (5-way) symmetry.
• All members have a water vascular system which acts
like a line of suction cups along radial canals to tube
feet.
Phylum Chordata
• Lancets, terrestrial vertebrates are included in
this group
• The major evolutionary innovation in this
group is the notochord
• In all of the 50 thousand species, there are
four principal features
– Notochord
– Nerve Cord
– Pharyngeal slits
– Postanal Tail
Phylum Chordata
• Notochord is a stiff, but flexible rod that forms
beneath the nerve cord that acts to anchor internal
muscles, permitting rapid body movements
• Nerve cord is a single dorsal hollow nerve cord,
which the nerves that reach the different parts of the
body are attached
• Pharyngeal slits are a series of slits behind the mouth
into the pharynx ,which is a muscular tube the
mouth to the digestive tract and windpipe
• Postanal Tail is a tail that extends beyond the anus
Amniotic Egg
• While amphibians were the first land
animals, they are still largely tied to the
water for reproduction and resupply body
fluids.
• One key step was the development of a
waterproof skin.
• The evolution of the amniotic egg expanded
the success of vertebrates on land by
allowing reproduction on land.
• A series of specialized membranes function
in gas exchange, waste storage, and energy
storage for the developing embryo
Mammals
• Hair traps body heat.
• All mammal females supply nourishment to
their offspring in the form of milk.
– It is produced in special glands.
• The Monotremes (platypus and echidna)
actually lay eggs.
• Marsupials begin development internally,
but young are born are a very early stage
and do most of their development in a
pouch.
• In placental mammals, embryos complete
far more of their development in a special
support structure, the placenta.
Phylum
Porifera
Cnidaria
Platyhelminthes
Nematoda
Mollusca
Annelids
Arthropoda
Echinodermata
Chordata
Innovative Evolutionary
Traits
Includes