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.
The first racket rules allowed the racket and strings to be made of any materials, and did not limit the size, weight, or shape. Strings were required to interlace or be bonded at cross points at least a quarter inch (0.64 cm) and not more than a half inch (1.3 cm) apart. No attachments were allowed that might alter the flight of the ball, and the weight distribution along the longitudinal axis of the racket must not change in play.