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DescriptionOscarella lobularis is a thick, encrusting sponge that grows up to 10-30 cm in width and 3 cm in height. It forms fleshy colonies consisting of lobed, round nodules that are up to 1 cm in width and 1 cm in height. The upper surface of each nodule bears a circular oscula (exhalant pore) that is 0.5 - 1 cm in diameter and leads to a large, basal cavity, while the sides bear scattered ostia (inhalant pores). The skeleton lacks both spicules and spongin fibre. The sponge has a firm but soft, gelatinous texture and the surface is smooth with a velvety feel. The colour of the sponge is more intense on the nodules and is normally yellow to brown but may be occasionally red, green, violet or blue, marked with cream at the base.Oscarella lobularis is a filter-feeder. It grows by increasing its size from the outer edge of the colony. It reproduces by releasing short-lived ciliated larvae that, once settled, metamorphose into the adult form. The colour of this sponge may vary from a deep red when fully illuminated to a brown-greenish yellow in dark light. Oscarella lobularis could be mistaken for Oscarella tuberculata, although the latter does not occur in British and Irish waters.