Environmental Biology for Engineers and Scientists (Vaccari/Environmental Biology for Engineers and Scientists) || The Animals

✍ Scribed by Vaccari, David A.; Strom, Peter F.; Alleman, James E.

• Publisher: John Wiley & Sons, Inc.
• Year: 2005
• Tongue: English
• Weight: 225 KB
• Edition: 1
• Category: Article
• ISBN: 0471722391
• DOI: 10.1002/0471741795.ch8

✦ Synopsis

Animals are multicellular heterotrophs whose cells lack cell walls and that have a motile stage at some part of their life cycle. They are diploid and reproduce primarily by sexual reproduction. Some of the interactions between animals and the environmental effects of human activities are: Loss of wildlife habitat may cause extinction. Overharvesting may lead to depletion or extinction of species. Animals may be reservoirs for human diseases. Control of pests may cause pollution.

The animal kingdom is divided into 33 phyla. A few of them include familiar groups or organisms. However, quite a few are relatively unfamiliar, and most of these are small marine organisms. About 1.5 million animal species have been named, but these are probably only a fraction of those that exist. Table 8.1 summarizes the animal phyla, grouped according to an informal subdivision system.

8.1 REPRODUCTIVE STRATEGIES

Animals have a great variety of means of reproduction. Only a few of the simplest animals reproduce asexually. Cnidarians, such as hydra, reproduce by budding, the unequal division of an organism. Many invertebrates, such as sea stars, can reproduce by fragmentation, in which the organism can simply be broken in two, with each part then regenerating the missing portion. Asexual reproduction produces clones, individuals