Biology Reference
In-Depth Information
2. HISTORICAL PERSPECTIVE
In 1674, Antonie Van Leeuwenhoek, a draper fromDelft and an ama-
teur naturalist skilled in the polishing of lenses and construction of micro-
scopes capable of up to 275
magnification (
Ford, 1995
), sent a letter to
the Secretary of the Royal Society in London, describing 'many little ani-
malcules' that he had observed in a sample from a local lake (
Rothschild,
1989
). The term 'Protozoa' (first animals) was introduced by the German
naturalist Georg Goldfuss in 1820 for microscopic organisms within the
Kingdom Animalia (
Scamardella, 1999
). By the middle of the nineteenth
century, microscopic organisms were viewed as Protozoa (unicellular ani-
mals), Protophyta (primitive plants), Phytozoa (animal-like plants) and
Bacteria (regarded primarily as plants) (
Scamardella, 1999
). The British
naturalist John Hogg (1800-1869) used the term 'Protoctista' to denote
the microorganisms that share characteristics of both plants and animals.
The German naturalist Ernst Haeckel (1834-1919) introduced the term
'Protista' (primordial/first) to define organisms intermediate between plants
and animals. Over the next century, progress in the understanding of micro-
organisms was based primarily on traditional studies of morphology, phys-
iology and biochemistry. Concurrently, the distinction between prokaryote
and eukaryotes based only on the absence or presence of nuclei was intro-
duced by
Chatton (1925)
, and the term protozoa was superseded by Protista.
The advent of molecular phylogeny based on small-subunit ribosomal RNA
(SSU rRNA) sequences, pioneered by
Woese, Kandler, and Wheelis (1990)
helped to demonstrate that protists comprise numerous independently
evolved and widely diverse lineages (
Sogin, Morrison, Hinkle, &
Silberman, 1996; Sogin & Silberman, 1998
). Based on molecular phylogeny,
six clusters or supergroups of protists have been recognized (
Simpson &
Roger, 2002
): (1) the Opisthokonta, comprising animals (metazoans), fungi,
choanoflagellates and mesomycetozoa, (2) the Amoebozoa, grouping amoe-
bas, amoeba-flagellates and amitochonriate amoebas, (3) the Excavata,
encompassing oxymonads, parabasalids, jacobids, diplomonads, Euglenozoa
and Heterolobosea, (4) the Rhizaria, grouping the Foraminifera, Radiolaria
and Cercozoa, (5) the Archaeaplastida, comprising the Glaucophyte, red and
green algae and plants, and (6), the Chromalveolata, grouping the Alveolata
(ciliates, dinoflagellates and Apicomplexa), the Stramenopiles (brown algae,
diatoms, zoosporic fungi and opalinids) together with the Haptophyta and
Cryptophyceae (
Adl et al., 2005
). Protists are defined as eukaryotes with
