23.1 Animal Characteristics
KEY CONCEPT
Animals are diverse but share common
characteristics.
23.1 Animal Characteristics
Animals are the most physically diverse kingdom of
organisms.
• Animals range in size from 25-meter-long blue whales
to microscopic rotifers.
• Animals are found nearly everywhere on Earth.
23.1 Animal Characteristics
All animals share a set of characteristics.
• All animals share a unique set of derived
characters.
• Animal cells are
supported by collagen.
– three-stranded
protein
– found in bone,
skin, ligaments,
fingernails,
and hair
23.1 Animal Characteristics
• Animals are diploid and usually reproduce sexually.
– diploid parents produce diploid offspring
– do not have free-living haploid life stages
Diploid cells have two copies of each chromosome:
one copy from the mother and one from the father
23.1 Animal Characteristics
• Most animals have Hox genes.
– Homeotic genes control early development.
– Hox genes determine the position of cells differentiation.
– A Hox gene mutation leads to the development of a body
structure in the wrong position.
23.1 Animal Characteristics
• Differences in body plans result from differences in the
expression of Hox genes.
– Hox genes tell embryonic cells which body part to
become.
– Mutations in Hox genes led to the vast diversity of
animal species.
head
tail
fruit fly genes
human
HOX-B genes
tail
head
23.1 Animal Characteristics
Each animal phylum has a unique body plan.
• Vertebrates have an internal segmented backbone.
• Invertebrates do not have a backbone.
• Invertebrates encompass most animal groups.
23.1 Animal Characteristics
Animals are grouped using a variety of criteria.
• Three criteria are used to
categorize animals.
– body plan symmetry
– tissue layers
– developmental patterns
gastrovascular
cavity
mouth
mesoglea
brain
muscle
hearts
blood vessels
oral arms
mouth
segment
digestive track
nerve cord
tentacles
23.1 Animal Characteristics
• There are two types of body plan symmetry.
– bilateral symmetry: body divides equally along one plane
Animals with bilateral
symmetry can be
divided equally along
only one plane, which
splits an animal
into mirror-image
sides.
23.1 Animal Characteristics
• There are two types of body plan symmetry.
– bilateral symmetry: body divides equally along one plane
– radial symmetry: body arranged in circle around a
central axis
Animals with radial symmetry
have body parts arranged in a
circle around a central axis.
23.1 Animal Characteristics
Types of Symmetry
23.1 Animal Characteristics
• Bilateral animals have 3 distinct layers of tissue
• Radial animals have only 2
23.1 Animal Characteristics
Symmetry Practice
23.1 Animal Characteristics
Germ Layer Tissue
• Germ layer tissues are aligned in specific positions in an embryo
and eventually give rise to all of an animal’s tissues and organs.
– Endoderm-inner most layer, develops into the linings of the
digestive tract and much of the respiratory system
– Mesoderm-middle layer, gives rise to muscles and most internal
organs
– Ectoderm-outermost layer, gives rise to nervous system and skin
• Simpler organisms with radial symmetry only have endoderm and
ectoderm.
23.1 Animal Characteristics
23.1 Animal Characteristics
Body Cavities
• Acoelomates- have no coelom, or body cavity
• Pseudocoelomates-have a false or partially lined body
cavity with only 1 side being covered with mesoderm
• Coelomates-have a true body cavity, both sides of the
body cavity are lined with mesoderm
23.1 Animal Characteristics
23.1 Animal Characteristics
Gastrulation
• Gastrulation is an interior
movement of cells that results in a
reorganization of the embryo from a
simple spherical ball of cells, the
blastula, into a multi-layered
organism. Two types:
– Protostomes form mouth-first,
and anus second.
– Deuterostomes first form the
anus and then the mouth.
23.1 Animal Characteristics
A comparison of structure and genetics reveals the
evolutionary history of animals.
• Protostomes and deuterostomes are the two major
radiations on the animal phylogenetic tree.
NO TISSUES
RADIAL
lancelets,
vertebrates
sea stars,
sea urchins
crustaceans,
insects, spiders
Echinodermata
Nematoda Arthropoda
Chordata
roundworms
clams, snails,
octopuses
Segmented
worms
flatworms
Cnidaria Platyhelminthes Annelida
Mollusca
jellyfish, coral, anemones
sponges
Porifera
DUETEROSTOMES
PROTOSTOMES
23.1 Animal Characteristics
• The current organization of the animal kingdom shows
some unexpected relationships.
• Technological advancements
help to clarify evolutionary
relationships.