Distal ends of 4 main (equatorial) spicules forming large, triangular, latticed plates with quadrangular pores. Tropical spicules about 1/3 as long as equatorial, polar 1/2 as long, very thin, with sharp tips, basal part pear-shaped, inflated. Distal ends of secondary spicules with 1-2 pairs of thin opposing apophyses at right angles, which in turn also bear apophyses at right angles; these branches coalesce into a delicate meshwork. The number and degree of development of apophyses varies widely (may be absent altogether in young specimens); this variability led Haeckel (1887) to establish several species, which were subsequently synonymized by Schewiakoff (1926) into Lithoptera fenestrata. Length of main spicules: 0.24 mm; width of latticed meshwork: 0.32 mm; length of tropical spicules: 0.15 mm, polar: 0.12 mm.