Haplosyllis spongicola, the sponge worm, is a species of polychaete worm in the family Syllidae. It was previously classified as Syllis spongicola and is part of a species complex of closely related species that are difficult to distinguish morphologically and where the demarcation between them is unclear. It is found in shallow temperate, subtropical and tropical seas worldwide, wherever its host sponges are found. Source: Wikipedia (en)