About Tylodina fungina Gabb, 1865
Tylodina fungina Gabb, 1865 is a heterobranch gastropod that reaches approximately 3 to 6 cm in length. Its entire body is bright sulfur yellow, and it has an external, conical, limpet-like shell that ranges in color from white to pinkish brown, and is often covered in small brown bristles and marked with brown spots. Juvenile individuals are smaller than adults, and their shells are more translucent and flatter than adult shells; as juveniles grow, their shells become increasingly tall. This species has rolled rhinophores, with eyes positioned at the base of each rhinophore. Its overall shape resembles a capped mushroom, and its gills are located on the sides of its body, which gives it the common name "mushroom sidegill." It also has a second common name, yellow umbrella slug, which it shares with its close relative Tylodina perversa, a species that inhabits the northeastern Atlantic Ocean. Tylodina fungina is distributed in the eastern Pacific Ocean, ranging from Cayucos in San Luis Obispo County, California, south to Banderas Bay, Jalisco, Mexico, and it is also found in the Galapagos Islands. This species lives in the intertidal zone, and is frequently seen at underwater depths between 10 and 20 feet. In situ observations made along the Pacific coast of Mexico show that Tylodina fungina is specialized to feed on the yellow sulfur sponge Aplysina fistularis, and it is thought to feed exclusively on this sponge species.
