Architectural Pattern of an Animal

Chapter 9

The Appearance of Major Body Plans

• The Cambrian explosion earliest fossil appear of all major groups of living animals plus some groups that are only known from fossils.
• All major body plans appeared at this time.
• Result of extensive selection.
• Are limiting determinant of future adaptational variants.

550-505 MYA

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Body Plans

• One way in which zoologists categorize the diversity of animals is according to general features of morphology and development.
• A group of animal species that share the same level of organizational complexity is known as a grade.
• 5 different grades (simple to complex)
• cells, tissue, organ, organ system, organism

Hierarchical Organization – 5 Levels

• Protoplasmic grade of organization – protists are the simplest eukaryotes, but they still carry out life functions and show division of labor among the various cell structures.
• Metazoans are multicellular animals that have cells specialized for particular functions. This is the Cellular grade of organization.
• Shown by the simplest metazoans – Volvox, sponges.

simple sponge video. Focus on the simplicity but effectiveness of organism.

Hierarchical Organization – 5 Levels

• Cell-tissue Grade – Usually, specialized cells are grouped together and perform their common function as a coordinated unit, a tissue.
• Jellyfish
• Tissue-organ Grade – Tissues are then assembled into organs like the heart (primarily muscle tissue, but connective, nervous, and epithelial also present).
• Flatworms

parenchyma - main cells that make up organ

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stroma - cells in organ that help it

Hierarchical Organization – 5 Levels

• Organ-system grade – In the highest level of organization, organs work together as organ systems like the circulatory system.

Animal Body Plans

• Body plans are constrained by ancestry, major features may become modified, but are rarely lost.
• Animal body plans differ in their grade of organization, body symmetry, number of germ layers, and type of body cavity.

Symmetry

• Spherical symmetry occurs when any plane passing through the center divides the body into mirror image halves.
• Mostly found among the protists.

Symmetry

• Radial symmetry applies when more than two planes passing through the longitudinal axis can divide the organism into mirror image halves.
• Jellyfish
• Biradial symmetry – two planes will divide the organism.
• Comb jellies

Radiata Phyla

• comprised of jellyfish, corals, and sea anemones
• No front/back
• Weak swimmers
• Can interact with environment in all directions.

Symmetry

• Bilateral symmetry is found in organisms where one plane can pass through the organism dividing it into right and left halves.
• Better for directional movement.
• Monophyletic group called Bilateria.

Cephalization

• Bilateral symmetry is associated with cephalization, differentiation of a head.
• Nervous tissue, sense organs, and often the mouth are located in the head.
• Advantages for organisms moving head first – directional movement.
• Elongation along anteroposterior axis.

Regions of a Bilaterally Symmetrical Animal

• Anterior-posterior (transverse plane)
• Dorsal-ventral (frontal plane)
• Left-right (sagittal plane)
• Proximal-distal
• Medial-lateral

Developmental Patterns

Start with zygote

pg 184 shows overall development from gastula

Developmental Patterns

• Sponges develop only to blastula stage, then reorganize to form adult.
• Gastrulation allows animals to proceed to tissue level organization.
• Diploblastic – 2 germ layers
• Cnidarians, Ctenophores
• Triploblastic – 3 germ layers (has mesoderm)

Body Cavities

• Examples of body cavities include the gut, blastocoel, and a pseudocoel or coelom.
• The gut forms from the archenteron during gastrulation.
• The blastocoel persists in some, but usually fills with mesoderm.
• Pseudocoel and coelom are fluid filled body cavities that cushion organs and provide support.

Body Cavities

• In protostomes, mesoderm forms as endodermal cells from near the blastopore migrate into the blastocoel.
• Three body plans possible:
• Acoelomate (no body cavity)
• Pseudocoelomate (body cavity between endoderm & mesoderm)
• Coelomate (body cavity surrounded by mesoderm)

Body Cavities

• Coeloms surrounded by mesoderm can arise in two ways:
• Schizocoely – mesodermal cells fill the blastocoel, forming a solid band of tissue around the gut, then a space opens inside the mesodermal band.
• Enterocoely – portions of the gut lining form pockets that pinch off and form a ring of mesoderm.

Other Key Features of Body Plans

• In some organisms, the gut does not form a complete tube.
• Waste must come back out the mouth.
• Food must be digested & waste expelled before eating again.
• A complete gut forms a tube within a tube body plan.

Other Key Features of Body Plans

• Segmentation is a serial repetition of similar body segments along the body.
• Each segment is a metamere or somite.
• May include external & internal components.
• Obscured in many animals, like humans.
• Permits greater body mobility and complexity of structure & function.

Components of Metazoan Bodies

• Extracellular Components - noncellular components of metazoan animals:
• Body fluids
• Extracellular structural elements

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Tissue Structure and Function

• A tissue is a group of similar cells specialized for performing a common function.
• Different types of tissues have different structures that are suited to their functions.
• Tissues are classified into four main categories:
• Epithelial
• Connective
• Muscle
• Nervous

• Cellular Components - Tissues

Epithelial Tissue

• Epithelial tissue covers the outside of the body and lines organs and cavities within the body.
• Squamous, cuboidal, columnar.
• Simple vs. stratified.

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Connective Tissue

• Connective tissue functions mainly to bind and support other tissues.
• Contains sparsely packed cells scattered throughout an extracellular matrix.

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Muscle Tissue

• Muscle tissue is composed of long cells called muscle fibers capable of contracting in response to nerve signals.
• Smooth
• Skeletal
• Cardiac

Nervous Tissue

• Nervous tissue senses stimuli and transmits signals throughout the animal.
• A neuron (nerve cell) receive signals at the dendrites and send them out via the axons.

Complexity and Body Size

• Increased complexity allows for an increase in body size.
• Larger size decreases the surface area to volume ratio.
• Necessitates complex systems for respiration, nutrition, and excretion – diffusion not adequate.
• Buffers environmental fluctuation.
• Escape predators.

Complexity and Body Size

• Cost of maintaining body temperature is less per gram of body weight than in small animals.
• Energy costs of moving a gram of body weight over a given distance less for larger animals.