Invertebrate
Evolution

Kingdom: Animalia
Animal classification
placed into related
phyla or division
1. Invertebrates—
majority of
animals which
lack a
backbone
2. Vertebrate--
animals with a
backbone
Common Phyla:
Porifera
Cnidarians
Platyhelminthes
Nematodes
Annelids
Mollusks
Arthropods
Echinoderms
Chordates

Origin of Invertebrates
Invertebrate fossils, dating between
575 and 543 million years ago.

The Fossils
Flat
Plate shaped
Segmented
Bilateral symmetry
Soft tissues
Lived on shallow seas
Nutrients: surrounding water

Beginnings of Invertebrate
Diversity
By the Cambrian Period, 544
million years ago, some animals
had evolved shells, skeletons,
and other hard body parts.

The animals of the Burgess Shale
body symmetry
Segmentation
 skeleton
front and a back end
appendages adapted for many
functions

Invertebrate Phylogeny
features evolved during
the Cambrian period
such as:
tissues and organs
patterns of early
development
body symmetry
cephalization
segmentation
formation of three germ
layers and a coelom

Invertebrate Evolutionary
Relationships

Evolutionary trends toward
Greater size
Compartmentalization
Integration of
specialized
activities that keep
the organism alive

I. Level of Organization
Cellular: no true tissues;
sponges
Organ: have ectoderm,
endoderm, and mesoderm;
majority of animals
Tissue: have ectoderm and
endoderm; cnidarians like
hydra

Body
Symmetry
Asymmetrical
Radial
Symmetry
Bilateral symmetry

Cephalization
 concentration of sense organs and nerve
cells in the front of the body.

Type of Body Cavity
Acoelomate
Pseudocoelomate
Coelom

Acoelomate
Digestive sac
(from endoderm)
Tissue-filled region
(from mesoderm)
Body covering
(from ectoderm)

Pseudocoelomate
Body covering
(from ectoderm)
Muscle layer
(from mesoderm)
Digestive tract
(from endoderm)
Pseudocoelom

Coelomate Body covering
(from ectoderm)
Tissue layer
lining coelom
and suspending
internal organs
(from mesoderm)
Coelom
Digestive tract
(from endoderm)

Segmentation
Repetition of body parts
Leads to specialization of
body parts

Embryological
Development
Blastopore: first
opening during the
embryonic stages
of an organism

Sponges: Multicellular
Phylum Porifera
Saclike Body with many Pores
Filter Feeders
Asexual and Sexual Reproduction
Spicules

Simple Sponge Anatomy

Cnidarians
Jelly fishes, corals, sea
anemones
Radial, tentacled carnivores
Gastrovascular cavity
True epithelial tissues
with a jellylike matrix in
between
Simple nervous
system

Flatworms (Phylum Platyhelminthes)
Paired nerve cords
Simplest animals with
organ systems
Free-living
turbellarians

PhylumAnnelida
Muscles and fluid in
chambers act as a
hydrostatic skeleton
Nervous system
Digestive and excretory system
Closed circulatory
system
Segmented worms

secretory organ
head
end

Mollusks (Phylum Mollusca)
100,000 named species
Including gastropods (snails), bivalves (scallops), chitons,
nudibranchs, cephalopods

Cephalopods

Roundworms (Phylum Nematoda)
Organ systems in a
false coelom
A complete gut
Cylindrical body with bilateral
features
Some agricultural pests and
human parasites
Free-living decomposers
or parasites
More than 22,000 kinds of
roundworms

Parasitic Roundworms

Simple Arthropods
 Trilobite, millipede, centipede

Arthropod Characteristics
Specialized and fused
segments (wings)
Efficient respiratory and sensory
structures (eyes, antennae)
Jointed appendages
Hardened exoskeleton
Key arthropod adaptations

Echinoderms
Adults are radial, but bilateral
traits appear in larval stages
Water-vascular system with
tube feet
Exoskeleton with spines,
spicules, or plates of calcium
carbonate
Sea stars, sea urchins, sea
cucumbers, etc.

Summary Many important traits
evolved in
invertebrates.
segmentationCoelom formation
Cephalization
Symmetry
Organs
Tissues
Multicellurarity