Currently, only one species, Trichoplax adhaerens, is acknowledged to belong to the Placozoa. The Italian Francesco Saverio Monticelli described another species in 1893, which he found in the waters around Naples, naming it Treptoplax reptans.
A standard mallet has a head length of 9 to 9.5, and this is recommended for beginners. Expert players may use longer head lengths up to 12, as this is thought to make aiming more accurate and makes it harder to accidentally twist the mallet during the stroke.
Rackets used in racquetball cannot exceed 22 inches in length from its handle to the top. A tennis racket can be as long as 29 inches with a frame width of 12.5 inches. Racquetball uses balls that are made of hollow rubber, and tennis balls have a fabric cover.