The main idea
Despite the variety of shapes and forms, animals are built fundamentally the same (outside tube, inside tube, stuff in the middle). However, because these cheracters are so fundamental you don't think about them typically. We examine what these characters are and which animal groups share them.
Describe the defining characteristics of animals
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animals are multicellular heterotrophs that feed by ingestion -
molecular and morphological evidence suggests they probably evolved from colonial protists called choanoflagellates -
animals lack cell walls; instead, cells are held together by extracellular proteins and special intracellular junctions -
most animals have muscle and nerve cells for sensation and coordinated movement
Describe the general animal life cycle
Development typically proceeds through several stages:
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fertilization and formation of the zygote -
mitotic division to form a hollow ball of cells (the blastula) -
infolding of one side of the blastula to form the gastrula. - Taxa in which this opening (blastopore) becomes the mouth are called protostomes;
- Taxa in which this opening becomes the anus are called deuterostomes.
- These groups also have distinctive patterns of early cell division and coelom formation
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differentiation into tissue layers (see below). -
some groups develop directly into adults, while others first form a larva, which then undergoes a major change in body form (metamorphosis) to become the adult.
List the tissue layers in a typical animal embryo, and which tissues they generally create in an animal
Embryonic tissue layers give rise to specific tissues.
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ectoderm becomes the epidermis and nervous system -
endoderm becomes the digestive tract and associated organs -
mesoderm, where present, forms muscle, connective tissue, skeleton, circulatory system
Describe the four levels of organization found in animals
Levels of organization include:
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cellular: where different cell types are specialized to particular functions -
tissue: where cells of one or several types work together for common function, and are bound together with specialized junctions and basal lamina -
organ: where different tissues are bound together in a structure for one purpose -
organ system: where multiple organs coordinate for a particular function
Describe three different types of symmetry found in animals and the ecological/behavioral characters with which they correlate
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Symmetry is how an organism may be bisected to form pieces that are mirror images of each other. -
asymmetrical organisms have amorphous forms that cannot be equally bisected -
radially symmetrical organisms can be divided in any plane about at least one axis; these organisms have no "head", adapted to sedentary/planktonic life -
bilaterally symmetrical organisms can only be divided in one plane; such organisms have a "head" which is specialized for sensing the environment
List and describe the types and functions of animal body spaces
An internal body space functions
- forms a mechanical barrier between endoderm and ectoderm
- allows for the development and expansion of new structures
- serves as a storage chamber for body products (e.g. gametes)
- provides a circulation medium
- serves as a hydrostatic skeleton
Body space types:
- a true coelom is a fluid-filled space completely lined by mesoderm
- a pseudocoelom is only lined with mesoderm on one side (usually the outside), and is most common in small animals
- acoelomates have no internal body space, and must have spongy mesoderm that allows circulation
Describe the differences between Protostomes and Deuterostomes
These characters have been used to define groups of phyla, based on characters of animal development.
| Character | Protostome | Deuterostome |
| blastopore fate | mouth | anus or other |
| embryonic cleavage | spiral | radial |
| coelom formation | cell mass that breaks apart | outpocketing of gut |
| development | mosaic | regulative |
Describe the construction and function of a hydrostatic skeleton
See text 18.3
Describe the five-stage hypothesis for the evolution of animals from protists.
See text 18.2
Characterize the nine major animal phyla in terms of the following traits
- tissue layers
- symmetry
- body space
- level of organization (and completeness, specialization of digestive system)
- protostomes versus deuterostomes
- unique characters
These will be characters to watch in the lectures as we go through the phyla. Use your quiz 4 from lab to begin a table to organize this information.
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