Guinea pig, also commonly called the cavy, is a species of rodent belonging to the family Caviidae and the genus Cavia. Despite their common name, these animals are not pigs, nor do they come from Guinea.

See pictures:
http://www.google.com.eg/images?hl=ar&q="guinea pig"&um=1&ie...

ولادة أرنب بلا أذنين يشبه الخنزير
ظن مراهق بريطاني أنه رأى خنزير غينيا يخرج من قفص الأرانب في حديقته، ولكن تبيّن له أن ذلك لم يكن سوى أرنب من دون اذنين. وأطلق على الأرنب إسم فنسنت، في إشارة إلى الرسام فان جوخ الذي قطع إحدى أذنيه عندما كان عمره 16 سنة. ومعروف عن خنزير غينيا أنه ينتمي إلى فئة القوارض و يقتات على الخضروات مثل الجزر والملفوف وليس له أذنان.
http://www.moheet.com/show_news.aspx?nid=203787&pg=1


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Note added at 9 hrs (2010-05-27 07:32:25 GMT)
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How the animals came to be thought of as "pigs" is not clear. They are built somewhat like pigs, with large heads relative to their bodies, stout necks, and rounded rumps with no tail of any consequence; some of the sounds they emit are very similar to those made by pigs, and they also spend a large amount of time eating.

The origin of "guinea" in "guinea pig" is harder to explain. One theory is that the animals were brought to Europe by way of Guinea, leading people to think they had originated there. "Guinea" was also frequently used in English to refer generally to any far-off, unknown country, and so the name may simply be a colorful reference to the animal's foreignness. Another theory suggests the "guinea" in the name is a corruption of "Guiana", an area in South America, though the animals are not native to that region.