Invertebrates Facts

  • Invertebrates are multi-cellular and all the cells have different responsibilities to keep the animal alive.
  • Invertebrates have no backbone or bony skeleton or cells wall like all other animals.
  • Invertebrates like echinoderms do not have heads.
  • There are millions of invertebrates living in our house in the name of dust mites which are hardly visible to human eyes.
  • Invertebrates under a process called metamorphosis through which they change form as they grow.



Protozoa are single celled organisms that are very diverse groups. They vary in their size, shape, features, and habitat. The characteristic of the protozoa are usually liked with other animals. The most common characteristic of the protozoa are mobility and heterotrophy. Protozoa are grouped in the kingdom Protista.

There are about 92,000 described species of protozoa in the world. The protozoa can be seen in all the habitats including freshwater, marine water, and terrestrial soil. Most of the protozoa are the agents for human diseases like malarial and parasitic diseases.

Normally the protozoa range from 10 to micrometer but some has the capacity to grow up to 1mm. The protozoa cannot be seen with the naked eye. They can be seen only under the microscope. The protozoa move with the help of flagella a whip like tail structure. Protozoa reproduce through both sexually and asexually means. To know more about their characteristics refer to the page Characteristic of Protozoa.

Protozoa prey on unicellular and filamentous algae as a predator. In the food chain the protozoa play a very important role both as herbivores and consumers. They mainly control the growth of bacterial population. The protozoa in take their food with the help of the cell membrane. Some of the protozoa surround their prey and swallow them and some others have an opening called the mouth pores through which they sweep the food. The foods eaten by them are digested in the vacuoles a stomach like compartments.

The protozoa have a skeletal structure called a Pellicle which consists of the plasma membrane and cytoskeleton. Plasma membrane act as the outer surface and the cytoskeleton consists of the additional membranes, microtubules, plates, and microfilaments. The pellicle is in the shape of the cell. To know more about the body structures of the take a visit to the page Anatomy of the Protozoa.

Protozoa can be further classified on the basis of locomotion. They are:

  • Flagellates
  • Amoeboids
  • Sporozoans
  • Ciliates

To get a brief idea about each classification move to the page Classification of Protozoa.

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