|Zoocide: is a chemical agent that kills animals.
DEFINITION OF ZOOLOGY
Zoology is the study of the animal kingdom and also studies the relationships between different animals. Zoologists classify animals in much the same way as botanists classify plants. From the farmers point of view it is necessary to have knowledge of taxonomy because some zoocidal chemicals are specific to particular groups of animals, e.g. a nematacide will only kill nematode worms. An acaracide will only kill ticks and mites and anything else affected is coincidental.
- THE ANIMAL CELL
The animal cell does not possess a cell wall and normally does not have a cell vacuole. Animal cells do, however, have a cell membrane, a nucleus and organelles such as mitochondria. Animal cells never possess chloroplasts.
- CLASSIFICATION OF THE ANIMAL KINGDOM
- Taxonomic Method: The methods used to classify the animal kingdom are much the same as those used to classify the plant kingdom. There are a number of ways of classifying, however, the basic method is the same. Essentially, the animal kingdom is divided into a number by Phyla. These phyla are further sub-divided into classes. The classes are divided into orders and these into families containing genera and ultimately species. The scientific name for each animal is binomial, using first the genus name and then the species name.
- The Major Phyla: The animal kingdom can first be divided into two subkingdoms. Firstly, the protozoa – the single celled animals and secondly, the Metazoa – the multi-celled animals. The sub-kingdom protozoa have only one phylum. Protozoa can be divided into four classes: See Diagramme 1.1 below.
THESE FOUR CLASSES ARE:
- Metazoa: The metazoa can be divided into those multi-celled organisms possessing a digestive cavity and those without. These two groups are called the Parazoa, containing one phylum, the Poritera which are the sponges. The latter with a digestive cavity are called the Enterazoa.
- Enterazoa: The enterazoa is further divided into two divisions
- Triploblastica and Diploblastica. The distinction between the two is based on the development of the embryo in the early stages. In diploblastic animals, the animal grows from two layers of tissue with a space between them (mesoglea) usually filled with fluid. This division contains only one phylum, the Coelentrates which are the jelly-fish like organisms.
The Triploblastic organisms develop from embryos that have three layers of tissues. See Figure 1 below.
In some triploblastic animals, the third tissue is actually separated into an inner and outer layer of tissue between which is a fluid filled cavity called the Coelom and it is in this cavity that the organs of the higher animals develop. This gives rise to the Triploblastic animals being divided into those with a body cavity Eucoelomata and those without the Acoelomata. These are the two sections. These two sections are further divided up into many phyla of which only a few are mentioned in Figure 1.
The agriculturally important ones will be discussed in later lessons.
Figure 1: Classification Based on Embryo Development
Figure 1 continued: Classification Based on Embryo Development