Myxilla incrustans
Myxilla incrustans is a species of demosponge. It is an encrusting species and is usually yellow. Description. "M. incrustans" is an encrusting sponge occurring in patches up to across and high. It is usually some shade of yellow but can range through orange, pink and white. It has a bubbly-looking appearance with internal channels visible through the surface and large, raised oscules. The consistency is fairly soft and elastic but the surface feels crisp because of the vertical spicule bundles supporting it. The skeleton is built out of tornotes, megascleres with spear-shaped ends with tiny spines  on them. The microscleres are a mixture of curved, shovel-like chelae and "C"-shaped sigmas. Several other similar sponges grow in the same habitats and microscopic examination is necessary to identify the species. Distribution. "M. incrustans" is found in the Arctic, round Bear Island and the Faroe Islands, on the coasts of Norway and south along the Atlantic coast to the Mediterranean Sea. In these areas, it is usually found between low-water mark and a depth of on vertical rocks and sites with clean water exposed to strong tidal flows. It also occurs in the northwest Pacific Ocean and  Japanese waters. Here it is often found growing on the shells of clams in the genus "Chlamys". Biology. "M. incrustans" is viviparous and in the months of August and September, developing embryos are sometimes found inside the tissues. These are spherical and measure about across before becoming detached. Initiation of the sexual processes involved in reproduction depends on the water temperature. The male tissue releases sperm into the water column. These may get sucked into another sponge, and then fertilisation takes place. About 7% to 12% of the maternal tissue of the sponge is used up in the reproductive process , and there is some localized destruction of the tissue.