Invertebrates – Division of Animals without Backbone

You are doing a survey of invertebrate characteristics with the graphic organizer

Evolutionary Trends in Invertebrates: 1.Tissue Two tissue layers  three tissue layers Tissue Specialization (Tissue Derminatization) Body Cavities: Acoelomates  Coelomates 2.Asymmetry  radial  bilateral 3.Protostomes  Deuterostomes Protostomes: Mouth from Blastopore Deuterostome: Anus from Blastopore

Circulatory System –Open  Closed circulatory system –Heart-like Structures (like aortic arches)  Hearts Digestive System and Excretion –One opening  Two openings Nervous System –Trend to toward cephalization and centralized nervous system that is “controlled” by brain –More developed senses (Flatworms “Eyespot” and Eyes) –Stupid  Less Stupid

Reproduction –Asexual  Sexual –External fertilization  Internal Fertilization

Tissues A group of similar cells that work together to carry out a job. There are four types of tissue: 1.Connective 2.Muscle 3.Epithelial 4.Nervous

Symmetry There are four major types of symmetry –Asymmetry –Spherical symmetry –Radial symmetry –Bilateral symmetry

Body Cavities Acoelemates like flatworms or jellyfish Pseudocoelemates like roundworms Coelomates like mollusks, arthropods, and echinoderms

Coelomate Evolution - body cavities that develops within the mesoderm Dorsal Cranial (cephalization) Spinal Ventral Thoracic Abdominal

Invertebrate body plans Acoelomate with 2 germ layers –without a coelom –has endoderm –has ectoderm –Example – sponges and cnidarians

Acoelomates Have 3 germ layers –No coelom –Endoderm, ectoderm (1), mesoderm (2) –Flatworms are an example

True Coelomates Have three tissue layers –Endoderm, Mesoderm, Ectoderm Have a coelom within the mesoderm You are one!

Comparative Body Plans Which do you think is the most primitive / advanced? Why?

Further classification of Animals with Coeloms is by embryonic development TWO MAJOR LINEAGES Protostomes or Deuterostomes

Protostomes Blastopore becomes the mouth Second opening becomes the anus Coelom formed via schizocoely (cleavage) Circulatory system primitively dorsal Nervous system primitively ventral Phyla Mollusca, Annelida, Arthropoda and others

Coelom formed via schizocoely

Deuterostomes Blastopore becomes the anus Second opening becomes the mouth Coelom formed via enterocoely Circulatory system primitively ventral Nervous system primitively dorsal Phyla Echinodermata (starfish), Hemichordata (sea feathers) and others

Coelom formed via enterocoely

Cephalization Consider the presence of Nervous tissue in lower invertebrates. Do they have a brain? Are they able to respond to stimuli? The sponge has no nervous tissue at all and thus no cephalization The cnidarians have a neural net but no central processing location.

Cephalization Platyhelminthes is the first with central processing point called a ganglia (nervous inputs can be gathered and responded to). This is an early “brain”. Cephalization tends to occur at the anterior end of the body.

Not all groups have cephalization. In fact, some have been successful with a complete absence of cephalization. But, the majority of successful animal groups have some degree of cephalization.

Skeletal Systems Hydrostatic skeleton Exoskeleton –Made of chitin Can become very heavy and limits the size that insects can ultimately grow to. Endoskeleton –Support, mineral storage and creates blood cells

Hydrostatic Skeleton

Exoskeleton

Endoskeleton

Integumentary – Development of Skin Layer Protects against drying out which is extremely significant as animals move onto land Keratin – protein found in skin that is a barrier against the evaporation of water.

CLOSEDOPEN

END