Alfonso,
  If you are publishing a paper, check with the editor how he or she
requires web sites to be cited.  Generally they look for the author, the
title of the page, the complete URL (which can be quite long; be sure to
copy it correctly), and the date when you last viewed the page.
  Some sites are quite stable, while others are fleeting.  When I wrote a
paper for a class that I had taken, I had 10 web sites listed.  I checked
them 2 days before the paper had to be turned in to my instructor and 3
were already gone! This is why some of us are against web publishing.  The
ICZN does allow descriptions of new taxa on the web as long as copies
(print or CD-ROM) are placed in several institutions  (I believe a minimum
of 5 institutions). Anyone interested in this should refer to the
International Code of Zoological Nomenclature, 4th. ed, 2000.

  Hope this helps.

Regards,
Charlie