As a group the protozoa are most primitive and are inhabiting the earth for about a billion and half years. Fossil forms of radiolaria and foraminiferans, half a billion years old, have been recorded. Origin: Pre-Cambrian Taxonomic Retrospect: Leeuwenhock (1676) first gave preliminary accounts of some protozoan forms after the discovery of microscope. Goldfuss (1818) coined the term Protozoa but [...]
In this article we will discuss about Protozoa:- 1. Nutrition in Protozoa 2. Respiration in Protozoa 3. Excretion 4. Reproduction. Nutrition in Protozoa: Nutrition is a process by which the individuals obtain nourishment. It includes ingestion, digestion, absorption and digestion. The nutrition of protozoa is manifested by following ways (Fig. 10.68): A. Holozoic or Zootrophic or Heterotrophic nutrition, B. Holotrophic [...]
The following points highlight the three main types of canal system encountered in sponges. The types are: 1. Ascon Type 2. Sycon Type 3. Leucon Type and 4. Rhagon Type. 1. Asconoid Type: The asconoid type of canal system is regarded to be the most simple and primitive grade of canal system. Asconoid type is present in these sponges whose [...]