n. (Zool.) Any species of sponge of the division Tetractinellida. Also used adjectively. [ 1913 Webster ]

‖n. pl. [ NL., from Gr. te`tra- tetra- + &unr_;, &unr_;, ray, spoke. ] (Zool.) A division of Spongiae in which the spicules are siliceous and have four branches diverging at right angles. Called also Tetractinellinae. [ 1913 Webster ]