Solitary and Colonial Forms
Animals may lead their lives either like individuals or in groups. While they exist as individuals, they are termed as solitary, but if they live in organised colonies, we name then colonial. Colonies are a form of intraspecific association in which the interests of an individual are subordinate to those of the whole group. In true colonies the individuals are organically connected together by living matter or by material secreted by them. The degree and extent of closeness among individuals in a colony may change considerably. True colonies are found just only in primitive groups with simple organisation, such as protozoans and coelenterates. In sponges it is difficult to ascertain if the branched animal is an individual or a colony. Colonial forms mainly reproduce asexually. In fact the colony results due to the failure of the individuals to separate. Each individual in a colony is known as a zooid.