| In filter-feeding tubicolous polychaetes the buccal cavity is not eversible and there is no proboscis. |
| Abdominal segments 1-6 have 1-2 pairs of eversible vesicles. |
| Nemertines however, lack a protective cuticle or exoskeleton as well as stalked eyes, but have a characteristic eversible proboscis. |
| The anteriorly situated, eversible ciliated pits resemble nuchal organs of polychaete annelids. |
| The eversible sacs on the abdominal segments are shown, some protruded and some retracted. |
| Phylum Nemertea contains about 1,150 species of unsegmented worms that possess an eversible proboscis contained in a fluid-filled cavity or rhynchocoel. |
