Animals
The animal kingdom has been traditionally divided into two groups: VERTEBRATES and INVERTEBRATES. On account of intermediate forms, the phylum Chordata was introduced by Bateson in 1885.
Comprehensive information about the present day system of taxonomy, which is based on Karl Woese's 1990 paper, is found at tolweb.org. Another outline of taxonomy, giving more historical information, is found at http://sn2000.taxonomy.nl. The progression to vertebrates is as follows:
Animalia > Bilateria > Deuterostomia > Chordonia > Chordata > Vertebrata
The infrakingdom Chordonia was introduced by Haeckel in 1874.
The page https://www.angelfire.com/mo2/animals1/welcome.html at another angelfire site contains a fair amount of information about various animal species.The figure below illustrates biological taxonomy from the point of view of evolution
It is taken from the page http://www.evogeneao.com/tree.html, where it is explained in detail.
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1. Invertebrates
We will not concern ourselves much with such organisms as porifera (sponges) which lack nervous systems. Information on sponges can be found at
http://www.earthlife.net/inverts/porifera.hmtl
The phylum Cnidaria (jellyfish, sea anemones, corals, hydra, etc.) have nervous systems but lack brains. To quote from the page "Introduction to Cnidaria" at ucmp berkeley:
Cnidarians are incredibly diverse in form, as evidenced by colonial siphonophores, massive medusae and corals, feathery hydroids, and box jellies with complex eyes.
The name Cnidaria comes from the Greek word "cnidos," which means stinging nettle. More information about jellyfish eyes may be found in the Discovery News Article "Box Jellyfish's Many Eyes See Contrast" dated 2 April 2007.
Cnidaria are not bilateria; among the most primitive of bilateria are the nematodes. The nematode species CAENORHABDITIS ELEGANS, a 1 millimeter long worm with 959 cells that eats bacteria, was intensively investigated in the 1970s, leading to the award of the Nobel Prize in Physiology/Medicine 2002 to Sydney Brenner, Robert Horvitz and John Sulston. Bilateria include the following well known invertebrate phyla
See "Meet the Invertebrates" at can-do.com for further information on these.
The phylum Mollusca deserves special mention. The molluscs are a large and diverse group of soft bodied unsegmented animals, including familiar animals like snails, clams, squid and octopi. When Linnaeus was formulating his system of binomial nomenclature the molluscs were grouped (along with most invertebrates) under vermes, worms. The name Mollusca was first used by the great French biologist Cuvier in 1789 to refer to cephalopods like squids and cuttlefish. It was later extended to include other organisms, such as snails and bivalves. Molluscs first appeared during the earliest Cambrian period.
The class Cephalopodia is the group in which octopuses, squid, cuttlefishes and nautiluses are classified. Cephalopods are the most intelligent of invertebrates. They have eyes and other senses that rival those of humans. The Long-finned Squid (Loligo pealei) has extremely large nerve cells (neurons) and was used in the late 1950s for the experimental study of neurophysiology. An introduction to the history of this subject is found in my two Fropper blog postings
The branch Deuterostomia consists of the classes
Further information on Deuterostomia and Chordata can be found on the page
http://www.nearctica.com/nathist/chordata/primchor.htm
where they are described as Primitive Chordates. Echinoderms are considered to be the closest relatives of the chordates and hemichordates from the point of view of evolution. This is a significant departure from the Linnaeus classification.
Tentative version created: 17 Oct 09
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