Palaeos Eukarya: Contents

Eukarya

Life ├─Eubacteria └─┬─Archaea └─Eukarya ├─Metamonada └─┬─Discicristata └─┬─Rhizaria └─┬─┬─┬─Alveolata │ │ └─Chromista │ └─Plantae └─Stem Metazoa ├─Fungi └─Metazoa

Diversity of Eukarya: 1: Vanella (Amoebozoa). 2: unidentified foraminifer (Rhizaria). 3: Cryptomonas (Hacrobia). 4: Ceriodaphnia (Opisthokonta). 5: Scytosiphon (Stramenopila). 6: Sedum (Plantae). 7: Paramecium (Alveolata). 8: Phacus (Excavata).
Original url (includes phylogeny and basic intro) - SHIGEN; see also the Tree of Life Page and Wikipedia page for more detailed introductions.

Eukarya

The Eukarya constitute the third great domain of life on Earth (following here Woese's Three Domain model), being characterised by a larger and more complex cellular organisation, and infinitely greater diversity of form.

If the prokaryotes (the Eubacteria and Archaea, and perhaps whatever other unknown organisms were around during the Archean eon) are metabolically diverse but morphogenetically similar, the eukaryotes are the opposite. And while they only make up a small proportion of life on Earth (the biosphere has always been, and remains, predominately and primarily prokaryote) they are - at least from an anthropocentric perspective - more interesting because of their larger size, greater complexity, and far more rapid evolutionary rates. And all of this is due to their discovery of sex, which allows a far more efficient means of shuffling of genetic material.

Traditionally, and anthropocentrically, especially in the 19th through to the mid 20th century, eukaryotes have been classified according to two rather arbitrary parameters: whether they are single celled or multi-celled, and whether they are plant-like (non-motile, autotrophic, photosynthetic) or animal like (motile, heterotrophic feeding on other organisms). The plant like unicellular ones, and plant-like aquatic forms that lack a vascular system, are called algae, a taxonomic wastebasket term if ever there was one. The animal like unicellular ones are called "protozoa" and are implied to be the crude ancestors of complex, multicellular animals, just as land plants are said to have evolved from "algae".

Although this long out-dated explanation will not be used here, although as a compromise to popular understanding, as well as organisational convenience, we have included pages on the unicellular eukaryotes, and the multicellular "algae" or "seaweed", in the current directory, corresponding to the Protista of Whittaker and Margulis.

The problem unfortunately (for phylogenetic enthusiasts and paleo geeks) is that the great majority of eukaryotes are both very small (being single celled) and - apart from some hard shelled amoeboid like forms - soft-bodied. Not only do they rarely fossilise, but conflicting molecular phylogenies proposed by different workers in the field seems to imply that it almost impossible to work out their evolutionary relationships. This will not prevent us from making a fool of ourselves by including our own equally unsatisfactory phylogeny, based on a rough consensus of current positions (in those rare areas where there is actually any agreement) along with some wild guesses and hopeless speculation.

The current unit then is divided into about a dozen units, the amount of pages given to each are totally disproportionate to the importance of the group in microbiology or the natural world. However, it is planned to have a decent coverage of the foraminifera (under Rhizaria) as these shelled amoeba-like forms have a very good fossil record. MAK

Eukarya

Eukarya

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