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:PoriferaCnidariansPlatyhelminthesNematodesAnnelidsMollusksArthropodsEchinodermsChordates

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

The FossilsFlat

Plate shaped

SegmentedBilateral

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 symmetrySegmentation skeletonfront and a back endappendages adapted for many

functions

Invertebrate Phylogenyfeatures evolved during the Cambrian period such as:

tissues and organspatterns of early

developmentbody symmetrycephalizationsegmentationformation of three

germ layers and a coelom

Invertebrate Evolutionary Relationships

What are the major trends in invertebrate evolution?

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 Symmet

ry

Asymmetrical

Radial Symmet

ry

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 layerlining coelomand suspendinginternal organs(from mesoderm)

Coelom

Digestive tract(from endoderm)

Segmentation

Repetition of body partsLeads to specialization of

body parts

Embryological Development

Blastopore: first

opening during the embryonic stages of an organism

INVERTEBRATE FORMS

AND FUNCTIONS

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

Phylum Annelida

Muscles and fluid in chambers act as a hydrostatic skeletonNervous

system

Digestive and excretory system

Closed circulatory system

Segmented worms

secretory organ

headend

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

CephalizationSymmetry

Organs

Tissues

Multicellurarity