Animal Architecture Zoology

What is an Animal? An animal is a living organism that is multicellular, eukaryotic, heterotrophic, and lacks cell walls. Multicellular means an animal is made up of many cells. Eukaryotic means a cell that has a membrane-bound nucleus, and membrane-bound organelles. Heterotrophic means an organism that consumes plants or autotrophs. Animals have cell membranes but not cell walls.

Animal Body plans Metazoa – multicellular animals Currently there are 32 phyla of metazoans – each phylum is characterized by a distinctive body plan and an array of biological properties that set it apart from other phyla Animal Body Plans differ in: Level of Organization Symmetry Number of Embryonic Germ Layers Form and Number of Body Cavities

hierarchical organization of animal complexity There are 5 major levels of organization. Each level is more complex than the preceding one and builds upon it in a hierarchical manner

5 Levels of Organization Protoplasmic level: found in unicellular organisms; unspecialized cell, all life functions take place in a single cell Cellular level: an aggregation of specialized cells; division of labor is evident Cell-Tissue level: an aggregation of similar cells into definite patterns or layers; no or few true organs Tissue-Organ level: an aggregation of tissues into organs; no or few true organ-systems Organ-System level: When organs work together to perform some function; most animal phyla demonstrate this level of organization

Levels of Organization Animals are made up of a complex system of cells. Cells make up different tissues of animal’s bodies. Tissues make up different organs in animal’s bodies. And organs make up different organ systems.

Animal Body Symmetry Symmetry in animals refers to the way in which a plane or planes of axis can divide the body. Animals with radial symmetry can be divided into similar halves by more than two planes. (examples include jellyfish, sea urchins, sea anemones etc.) Animals with bilateral symmetry can be divided into equal left and right halves along the mid-sagittal plane. Animals with bilateral symmetry also exhibit cephalization (they have a head with a concentration of nervous tissue).

Animal Body Symmetry

Anatomical Orientation When studying the anatomy of animals, it is necessary to use terminology to describe directions, planes, and points of reference. Anterior/Posterior: A direction on an animals body referring to towards the head and/or tail. Dorsal/Ventral: A direction on an animals body referring to towards the spine and/or belly. Medial/Lateral: A direction referring to towards or away from the midline or mid-sagittal plane of the body. Distal/Proximal: A direction referring to farther away from and closer to another point of reference.

Anatomical Orientation

Anatomical Orientation Sagittal plane: An imaginary line or axis that goes through the body separating left and right halves. Frontal plane: An imaginary line or axis that goes through the body separating dorsal and ventral halves or sections. Transverse plane: An imaginary line or axis that goes through the body separating anterior and posterior halves or sections. Oral/Aboral: Animals with radial symmetry, oral refers to the mouth side, aboral is opposite of oral.

Anatomical Orientation

Developing Life Gametes – eggs and sperm/haploid sex cells Zygote- the fertilized egg. Blastula-a hollow sphere of cells. Blastopore - the point where folding begins. Gastrula-as the blastula enlarges, it cups inward on one side. Embryo – An organism in its early stages of development

Cleavage

Cleavage a sharp division; a split. cell division, especially of a fertilized egg cell. the splitting of rocks or crystals in a preferred plane or direction.

Cleavage cell division, especially of a fertilized egg cell (zygote). Each smaller cell is called a blastomere.

Cleavage the splitting of rocks or crystals in a preferred plane or direction.

Pattern of body development:

Pattern of body development: Zygote- the fertilized egg.

Blastula-a hollow sphere of cells.

Early Embryonic Development There are two ways that a blastula can form Some animals (like echinoderms and chordates) exhibit radial cleavage, in which the cleavage planes are symmetrical. Other animals (like molluscs and annelids) exhibit spiral cleavage, in which the cells divide in a spiral or asymmetrical pattern.

Radial vs. Spiral Cleavage

Body Plan Development Cleavage continues to occur in the zygote until the dividing cells begin to form a fluid-filled ball of cells which is called a blastula. Inside the blastula is a fluid-filled cavity called a blastocoel. In most animals, the blastula folds and develops into a two-layered organism called a gastrula. The gastrula is made up of two layers called the endoderm and ectoderm. Later on these will form the outer and inner tissues and organs of the body.

Blastopore - the point where folding begins.

Gastrula Gastrula-as the blastula enlarges, it cups inward on one side.

Early Embryonic Development in Animals

Tissue differentiation These layers of cells become specific structures and organs in the animal.

Germ layers: Ectoderm - cells on the outside of the gastrula that become the body covering. Mesoderm - a middle layer of cells that forms the muscles and interior organs. Endoderm - cells on the inside of the gastrula that become the lining of the gut.

Body Cavities The gastrocoel (cavity inside the gastrula) develops into a digestive cavity in most adult animals. Some animals such as the sea anemone never advance beyond the gastrula stage. In the sea anemone, the opening or blastopore becomes the opening to the gastrovascular cavity. In most animals a third germ layer develops after the gastrula stage called the mesoderm.

Body Cavities In other animals, mesoderm completely fills the internal body cavity. This type of body cavity is without a coelom. These organisms are referred to as acoelomate. In some animals, the mesoderm lies along the outer edge of the ectoderm, but not along the endoderm. These types of organisms are referred to as pseudocoelomate, meaning “false coelom”.

Body Cavities And lastly the body cavity of most animals are eucoelomate or “true coelomate”. Usually the cavity is just referred to as simply a coelomate body cavity. In this body plan, the mesoderm completely lines the endoderm and ectoderm. A true coelom or body cavity allows much more flexibility and space for internal organs. Larger and more complex organisms have a coelomate body cavity.

Body Cavities

Body Cavities

Animal Development Another main difference in the way animals develop is the development of the blastopore, or the opening that forms the mouth or anus. In protostomes, which means “mouth first”, the blastopore develops into the mouth. (found in annelids, mulluscs, and arthropods). In deuterostomes, which means “mouth second”, the blastopore develops into the anus. (found in echinoderms and chordates).

Protostomes vs. Deuterostomes

Development of animals and their body cavities In coelomate animals if the coelom forms from mesoderm spreading out in the blastopore region, this pattern of coelom development is called schizocoelous development. In coelomate animals if the coelom forms from pouches that pinch off from a region of the endoderm and enlarge to form the coelom, this pattern of coelom development is called enterocoelous development.

Animal Development

Differentiation: the Fate of the germ cell layers Totipotent cells can form all the cell types in a body, plus the extraembryonic, or placental, cells. Embryonic cells within the first couple of cell divisions after fertilization are the only cells that are totipotent.

Pluripotent cells can give rise to all of the cell types that make up the body; embryonic stem cells are considered pluripotent.

Multipotent cells can develop into more than one cell type, but are more limited than pluripotent cells; adult stem cells and cord blood stem cells are considered multipotent. As the embryo develops, the potential of the cells change and cell differentiation occurs Cell Differentiation is the development of cells that have specialized functions

The ectoderm The ectoderm will form the outer components of the body, such as skin, hair, and mammary glands, as well as part of the nervous system Following gastrulation, a section of the ectoderm folds inward, creating a groove that closes and forms the neural tube, which gives rise to the central nervous system. Ectoderm also forms the neural crest, which helps to form structures of the face and brain.

The endoderm The endoderm produced during gastrulation will form the lining of the digestive tract, as well as that of the lungs and thyroid.

The mesoderm For animals with three germ layers, interactions between the ectoderm and endoderm induce the development of mesoderm. The mesoderm forms skeletal muscle, bone, connective tissue, the heart, and the urogenital system.

The mesoderm Due to the evolution of the mesoderm, triploblastic animals develop visceral organs such as stomachs and intestines, rather than retaining the open digestive cavity characteristic of diploblastic animals.

The Development of Tissues Eventually the germ layers (ectoderm, endoderm, and mesoderm) begin to specialize to form tissues. All of the body tissues of animals are comprised of one of the four basic tissue types. Epithelial tissue Connective tissue Muscular tissue Nervous tissue

Body Tissues