That which we share...and that which makes us unique:

Uncovering the Key Similarites and Differences Between the Cephalochordata, Urochordata and other Groups

Why Find Similarities And Differences?

The Earth is a vibrant environment that beams with biodiversity and is home to millions of species!  While estimates of the total diversity of life range from 5 million to 10 million species, these species are grouped into just five kingdoms (Burpee-Barlow et al. 2001).  Within (and sometimes between) these kingdoms, important morphological and embryological similarities can be discovered which can assist in finding evolutionary connections and links between organisms (Burpee-Barlow et al. 2001).  Finding similarities and differences is important in understanding the relationships between the Chordata and other groups.  Finding patterns can help in understanding the evolution of the uro- and cephalochordates can give insight to the structural evolution of the phyla.  

Making Key Connections: Vertebrates And Nonvertebrates

As Homo sapiens, we have vested interest in studying urochordates and cephalochordates due to their close evolutionary connection with human beings.  The body structure of the Urochordata and the Cephalochordata is a simplified version of the body structure of the vertebrate and lacks many of the "additional features that evolved in vertebrates" (Campbell et al. 1999).  The study of the Urochordata and Cephalochordata can "provide clues to the origin of vertebrates" (Campbell et al. 1999).  While all chordates are characterized by possessing, even if only during embryonic development, a notocord, a dorsal, hollow nerve cord, pharyngeal slits and a muscular postanal tail, vertebrates have evolved several advanced and structurally complex characteristics not found in urochordates and cephlochordates.  These are characterized by increased size and activity including a neural crest, cephalization and a closed circulatory system. Major innovations in vertebrate evolution include jaws, paired appendages, lungs, legs, the amniotic egg, hair, feathers, and changes in metabolism  (Campbell et al. 1999).    

Classification Of Phylum Chordata

http://www-biol.paisley.ac.uk/courses/Tatner/biomedia/units/chor10.htm

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