NEW YORK.- Sculptor Muriel Castanis, 80, died inManhattan due to lung failure. She sculpted draped figures which are all over the United States. She was born Muriel Brunner in 1928 and studied at the High School of Music and Art in New York. She started working as an artist in 1964. In 1980 her works sold out at OK Harris Works of Art in Manhattan, which represented her.