FURTHER PHYLOGENETIC CONSIDERATION OF PROTOZOANS

1. TOPIC: FURTHER
PHYLOGENETIC
CONSIDERATION OF
PROTOZOANS

2. FURTHER PHYLOGENETIC CONSIDERATION OF
PROTOZOANS
Introduction:
Protozoa originated about 1.5 billion years ago.
There are 30,000 fossil species are known. But
only the forminiferans and radiolarians have well
established fossil records in Precambrian rocks.
 From the study of base sequences in ribosomal
RNA indicates that each of the seven protozoan
phyla probably had separate origins.
 In 1993 T. Cavalier-Smith proposed that the
protozoa be elevated to kingdom status with 18
phyla

3.  EVOLUTIONARY RELATIONSHIPS:
Cladogram showing the evolutionary relationships of
protozoa and other eukaryotes base on 18S
Ribosomal RNA sequence comparisons.
 This cladogram suggests that:
 Evolution along the nuclearline of descent was not
continuous but instead occurred in major epochs (an
epoch is a particular time period marked by distinctive
features and events)
 Five major evolutionary radiations are apparent for the
protozoa.
 The Mastigophora (e.g., Giardia) and Microspora (e.g.,
Nosema) are modern relatives of the earliest
major eukaryotic cell lines.
 Following the development of these protozoa, the other
groups of protozoa radiated off the nuclear line
of descent

4. PROTOZOAN TAXONOMY:
Excavata:
Most members of the Excavata possess a
cytostome and a posteriorly directed
flagellum.
Examples include Giaradia, Trichomonas,
Euglena, and the zooflagellate
Trypanosoma, which causes sleeping
sickness. Members of the Amoebozoa
possess pseudopodia.

5. AMOEBAZOANS:
 Amoebazoans use pseudopodia for
feeding and locomotion.
Examples include Amoeba, Naegleria, and
Entamoeba. Foraminiferans and
radiolarians
are common marine. Rhizaria that possess
thin pseudopodia (filopodia). Difflugia is a
typical example of this supergroup.

6. CHROMALVEOLATA
The Chromalveolata are a very
diverse supergroup of protists
protozoans.
 Members can be either autotrophic,
mixotrophic or heterotrophic. They
are all united in the common feature
of a plastid origin

7. ALVEOLATA
The Alveolata is a large subgroup that
includes the dinoflagellates, Apicomplexa and
Ciliophora. Apicomplexans are all parasites
and include Plasmodium and Toxoplasma,
which cause malaria and toxoplasmosis,
respectively.
 Many apicomplexans have a three-part life
cycle involving schizogony, gametogony, and
sporogony. The ciliates represent some of the
most complex protozoa. Ciliates possess cilia,
a
macronucleus and one or more micronuclei.

8. EVIDENCES
 Recent evidences are on the basis of study of
base sequences in ribosomal RNA. 'Most evidences
indicate that all the seven protozoan phyla have
different origins. Therefore. each group is different
from other. Thus protozoan have been given the
status of kingdom. Additional modification in this
scheme of classification have proposed. It is
possible that this scheme of classification with be
changed in future

9. FURTHER PHYLOGENETIC
CONSIDERATIONS
 Precise evolutionary relationships are
difficult to determine for the protozoa. The
fossils record does existis not particularly
helpful in deducing relationships. However,
ribosomal RNA sequence comparisons
indicate that each of the four protist super
groups probably had separate origin.

10. Cladogram showing evolutionary
relationships of protozoans and other
eukaryotes on the base of 18S ribosomal
RNA sequence comparison