Source : Webster's Revised Unabridged Dictionary (1913)

Tetractinellida \Te*trac`ti*nel"li*da\, n. pl. [NL., from Gr.
   te`tra- tetra- + ?, ?, ray, spoke.] (Zo["o]l.)
   A division of Spongi[ae] in which the spicules are siliceous
   and have four branches diverging at right angles. Called also
   {Tetractinellin[ae]}.