The body of Spongilla lacustris is characterized by small, spined microscleres that are almost equally distributed. The base of the body can be rounded or flat, bearing free, long, cylindrical branches with a bristly surface. The coloration of the sponge ranges from bright green to pale white or light gray. The oscula are small and star-shaped, with a well-developed dermal membrane. The consistency of the sponge is soft and compressed. The megascleres are sharply pointed, straight or slightly curved, and those with pointed ends (amphioxea) appear smooth. Their dimensions range from 0.26-0.42 mm in length and 6-9 µm in width. The microscleres are slender, long, and straight, and they are plentiful. The amphioxea have small and equal spines, with lengths and widths ranging from 0.07-0.09 mm and 3-6 µm, respectively. The spicules of the gemmule (gemmoscleres) are straight and stout, covered with strong curved spines on the amphioxea. Their dimensions range from 0.04-0.09 mm in length and 3-6 µm in width. Gemmules are numerous, large, spherical, or rounded, scattered all over the body. The pneumatic layer is granular and thick, with tangentially arranged pointed spicules. The diameter of the gemmules ranges from 0.50-0.82 mm.