The term zoology originates from the Greek term "zoo" meaning animal. Zoology is the study of animals. A person who studies animals is called a zoologist. With millions of species to study scientists have specialized along phylogenetic lines. that is to say they may concentrate in an area like invertebrates, fish, insects, bees, etc. (Worksheet: Fields of Study in Life Science)
Animals are multicellular, eukaryotic, heterotrophic organisms that lack cell walls. Most are capable of movement as adults. They are said to be motile. Locomotion or movement is often used in identifyiing animals. While most animals are motile, some can fool an observer into believing they are plants. Most of these live in the ocean. The sea lilies, sea fans, barnacles, and sea anemones are examples of sessile animals. As adults they have little or no movement.
The number of animal phyla differ depending on the who's classification scheme is used. In general this site employes the scheme of Margulis and Schwartz in their book... Five Kingdoms: An Illustrated Guide to the Phyla of Life on Earth, 2nd Edition. They have classified the animal Kingdom into 33 phyla.
The termsinvertebrates, animals without backbones, and the vertebrates, animals with a backbone are also used. Nearly 90% of all animals are invertebrates and most of them are insects in the phylum arthropoda.
Media Watch --- Outstanding. Monthly program guide to TV shows in science. Links to TV channels, Net Material, Internet Specials and Radio. --- http://www710.bonsai.com/watch/
Metazoa --- Produced by Arizona University. Phyla and classes including representative photographs. http://phylogeny.arizona.edu/tree/eukaryotes/animals/animals.html
Vocabulary can be a problem because the terms used are usually derived from the Greek and Latin languages. Before looking at Table 2 check learn the following prefixes and root words. They will help you to define the terms and thus have a better understanding of what the groups have in common.
Phylogeny refers to the evolutionary relationships among species. They are usually shown in tree diagrams. The following table shows the evolutionary relationships between the major phyla of animals. For more detailed information click on the following websites
More on phylogenetic systematics than you ever wanted to know.
*Table 2: Classification of the Metazoa (Multicellular Animals) Kingdom
*Table adapted from Zoology, 1997. BarCharts Inc. www.barcharts.com
Metazoa means "many celled animals". Organisms with many cells have some distinct advantages. They grow larger in size, have better mobility, maintain better internal homeostasis and are relatively independent of their environment. These advantages permit them to adapt to their environment. They are the result of a "division of labor" where cells specialize to carry out various functions. In doing so the individual cells become dependent on other cells. The down side to multicelluarity is that the failure a group of cells to carry out their function can result in the death of the organism.
Symmetry refers to balance. In nature there are three kinds of symmetry. Spherical, radial, and bilateral. The absence of symmetry is called asymmetry. Organisms in the animal kingdom with symmetry exhibit either radial or bilateral symmetry.
In radial symmetry the organism exhibits a circular arrangement with numerous planes that create identical parts. Radial symmetry is analogous to a pie in which the organism may be cut in several planes with each part (piece of pie) being identical. A organism with radial symmetry exhibits no left or right sides. It has a top (oral surface) and a bottom (aboral surface). Animals in the phyla cnidaria and echninodermata exhibit radial symmetry.
In bilateral symmetry a organism can be divided in only one plane producing two mirror image halves. (Note that we are only referring to the external surface when discussing symmetry.) This division produces a left and right side. It is found in animals with cephalization (concentration of sensory organs in the head). These animals move in the direction of their head.
Anatomical terms - the following terms are used to describe the position of structures relative to other structures or locations on the body. They often have a counter part with an opposite or converse meaning.
All methods of classification have a strong basis in morphological (structure) similarities. However, the presence of wings does not mean two organisms are closely related (i.e. insects and birds). The study of an organism's embryology (development of embryos) provides taxonomists with a power tool in constructing relationships. The development of all animals follows a similar pattern beginning with a fertilized egg cell known as a zygote. As each group of animals evolved it added more complexity to its development while repeating the history of its ancestors. This tendency was studied by Ernst Haeckel in 1866 referred to as "ontogeny recapitulates phylogeny".
Zygote ---> 2 cells ---> 4 cells ---> 8 cells ---> 16 cells ---> Morula (solid ball of cells) ---> Blastula [BLAST-choo-la] w/Blastrocoel chamber ---> Gastrula w/Blastopore and Archenteron (embryonic gut)
During the gastrula stage three germ layers develop. All other tissues come from these layers. They are the endoderm (inside skin), mesoderm (middle skin), and ectoderm (outside skin).
Animals that produce all three layers are known as triploblastic. Some animals only produce two layers, endoderm, and ectoderm. These are said to be diploblastic.
The following table shows the development processes characteristic of protostomes and deuterostomes.
Blastropore fate - The blastropore is the opening into the archenteron (embryonic gut) that developed in during gastrulation (formation of the gastrula). Some animals have an incomplete digestive track (one opening) but others have a complete digestive track (two openings). In animals with a complete digestive tract the blastopore may become a mouth or an anus depending on the genetic nature of the organism.
Aquatic free swimming invertebrates have one of three types of larva which are useful in identifying evolutionary relationships among the phyla. The plannula is free swimming, ciliated, with two body layers. They settle to the bottom and develop into a polyp colony. Trochophores are free swimming and bilaterally symmetrical. Mollusca and annelida phyla produce trochophores.Bipinnaria (dipleurula) larva are free swimming with a distinctive developmental pattern. The echinoderm phyla produce them.
Primitive vs. Advanced Animals