PHYLUM  PROTOZOA

Definition  and  Introduction

 All  unicellular ( or  acellular )  eukaryotic  animals.

Most  primitive (Gr. Protos = first=zoon= animals ) organisms  considered  animals  because  of heterotrophic nutrition  and motility .Although the whole  body is a single  minute cell . it  performs all vital activities  that are  essential  for an   activities  that are  essential  for an  independent  existence  as a complete  organism. About  50,000 species   (30,000 present  and 20,000  extinct ) are  so far know, but  the total  number  of individual  protozoans  in nature  must  be much  more than the  of  the  membrane   of any  other phylum.

Brief History

Protozoans  were first studied  by Leeuwenhoek 1677. The  name  Protozoa was  coined by Goldfuss 1871. The  branch  of their  study is called  protozoology .

Important characters

1.      Usually minute (0.001-3.00mm)  microscopic,  free-living  in water , damp   soil,  or decaying  organic  matter, Many parasitic in other animals  and plants  .Some  symbiotic  or commensal.  Solitary or colonial. Free moving or sessile.

2.        Body  symmetrical  or asymmetrical. Shape  variable , oval, elongated ,  spherical,  or otherwise , but  fixed in most  species  unstable and  ever-changing  in  some.

3.      Body  naked with  only the  plasma membrane , or  covered by a thin pellicle . Some with  a hard , horny,  limy or siliceous  covering called shell, test  or lorica.

4.      Division of  labour  exhibited by specialized cell structures or organelles formed of macromolecules. Hence , only  molecular or protoplasmic level of body  organization ,

5.      One  to several  nuclei,  mostly similar when more  than one, but  of two  types  ( unclear dimorphism )  in some .

6.      Locomotory organelles  pseudopodia,  flagella , or cilia,

7.      Nutrition  principally  heterotrophic ( animals  like)  holozoic , saprozoic  saprophytic (absorbing  liquid  substances of  animal or plant  origin from the sur-roundings or parasitic. Some  are  autotrophic  or holophytic  ( plant like)  but usually , these can also  carry  some kind of heterotrophic  mutrition  (mixotrophic) ,Digestion in  holozoic  protozoans  occurs in food  vacuoles with  the help  of lysosomal enzymes.

8.      If  necessary  the quantity of water is regulated ( osmo  regulation )  by one  or  more contractile  vacuoles.

9.      Gaseous exchange and excretion  by diffusion through  body  surface . Ammonia  is principal  nitrogenous  waste (ammonotelic).

10.  Reproduction asexual  or sexual. Asexual  by fission  or budding , sexual by  gametes or conjugation.

11.  Encystment common  for reproduction , dispersal or survival  during  adverse environmental  conditions.