Chapter 29Comparing Invertebrates Essential Question What comparisons can we make about the invertebrate phyla?
29.1Invertebrate Evolution Essential Question What are the major trends on invertebrate Evolution?
Origin of the Invertebrates fossils found (610 million years old) that seem to be developing embryos of modern multicellular animals Trace fossils (tracks and burrows made by soft-bodied animals) also found New field called molecular paleontology to study how different body plans developed Also studying changes in genes that can cause major changes in body structure
First Multicellular Animals Most were flat and lived at bottom of shallow seas Made of soft tissues that absorbed nutrients from surrounding water Some had photosynthetic algae living in bodies Segmented with bilateral symmetry Simple and little internal specialization
Beginnings of Invertebrate Diversity • Cambrian period (began 544 million years ago) has many fossils • Called Cambrian explosion because most moderns animal phyla first appeared in fossil record • Gives us much information about early body plans • During time before this animals developed specialized cells, tissues , and organs • Burgess Shale of Canada has many fossils • Trilobites • Annelid called Canadia
Invertebrate Phylogeny Indicates sequence that animals developed important features such as body symmetry, cephalization, segmentation, and formation of three germ layers and a coelom. Features evolved in Cambrian Period
Evolutionary Trends • Specialized cells, tissues, and organs • Body symmetry – all have symmetry except sponges • Radial – body parts extend from the center of the body; examples are cnidarians and echinoderms • Bilateral – have mirror images of left and right sides; examples are worms, mollusks, and arthropods • Cephalization • concentration of sense organs in the head • Allows animals to respond to environment better than simpler animals • Worms and arthropods have nerve cells arranges in structures called ganglia • More complex invertebrates have nerve cells that form an organ called a brain
Cont’d • Segmentation • Most invertebrates with bilateral symmetry have segmented bodies • Segments have become specialized for specific functions such as reproduction and digestion • allows animal to increase body size • Coelom formation • Coelom – body cavity • Complex animals are coelomates (gut completely lined with tissue derived from mesoderm) • Simpler animals such as sponges are acoelomate (no gut) • Some animals have a coelom partially lined with tissue derived from the mesoderm (pseudocoelomate)
Cont’d • Three germ layers • Endoderm - • Mesoderm • ectoderm • Embryological development • Most invertebrates, zygote divides to form a blastula (hollow ball of cells) • In protostomes, the blastopore (first opening of blastula) develops into a mouth; no anus forms; includes worms, arthropods and mollusks • In dueterostomes, the blastopore forms an anus first and then the mouth develops second (DAM); examples include echinoderms and chordates
General Characteristics of Main Groups of Invertebrates