What is "pluto monkey"

Pluto \Plu"to\, [Also spelled rop. .]n. [L., fr. Gr. ?.]

1. (Class. Myth.) The son of Saturn and Rhea, brother of Jupiter and Neptune; the dark and gloomy god of the Lower World.

2. The ninth planet of the Solar System, the smallest (5700 km radius) and most distant from the sun. The suggestion has been made that it more closely resembles a large close comet than a planet. Its orbit has an eccentricity of 0.248, larger than that of any other planet; it varies from 4.44 to 7.37 billion km distance from the sun.

   Pluto is an oddball among its eight sister planets. It's the smallest in both size and mass, and has the most elliptical orbit. It moves in a plane tilted markedly away from the other planets' orbits. Moreover, Pluto is the only planet made almost entirely of ice.
   --Ron Cohen (Science News, Feb. 27, 1999, p. 139)

   {Pluto monkey (Zo["o]l.), a long-tailed African monkey ( Cercopithecus pluto), having side whiskers. The general color is black, more or less grizzled; the frontal band is white.