The addition of the 23-year-old number eight, who stands at 6ft 2in and weighs 17 stone, is a welcome boost for coach Richard Hill, who currently only has Kai Horstmann able to fill the roll at the back of the pack.
Hill told the club's official website: "Richard is a young player who will be experiencing club rugby outside of Samoa for the very first time.
"He has been on tour in Europe before, but this will be a big change of culture. We will initially give him time to settle in and acclimatise.
"This is a big opportunity for him and if he can make an impression and prove himself then we will look to contract him for even longer.
"Richard is a talent and was very highly recommended by Brian Lima, who knows a good player after featuring in five World Cups. He is firmly regarded as a really big prospect for Samoa and one we believe can make big strides at Warriors."
Muagututia, who made his Test debut against Japan last year, added: "This is a great opportunity for me and a new start. It is exciting to join the Warriors and to play in England. I will play hard and for the future and hope to make a good impression with the supporters."
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The entire All Blacks apparel line has been updated for 2013/14. Check out the New Zealand All Blacks polo.
The Nike Tiempo is a solid rugby cleat and one of few styles still made from full-grain natural leather.
The Gilbert Blitz 8S rugby cleat is a great cleat at a great price of $69.99. Get a new pair of cleats today.
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Wear the crest of the British and Irish Lions on your t-shirt. A great look for the summer.
The All Blacks Performance t-shirt is black with hints of blue from the training jersey. Very Cool.
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The USA Rugby Pro Alternate rugby jersey is perfect for any fan of the Eagles. Get yours to wear during the summer Test matches.
The NEW All Blacks 2013/14 jersey has arrived at World Rugby Shop. Dare to wear the colors of the All Blacks.