Certain pycnogonids are so small that each of their very tiny muscles consists of only one single cell, surrounded by connective tissue. The anterior region consists of the proboscis, which has fairly limited dorsoventral and lateral movement, and three to four appendages including the s, which are used in caring for young and cleaning as well as courtship. In some species, the chelifores, palps and ovigers can be reduced or missing in adults. In those species that lack chelifores and palps, the proboscis is well developed and more mobile and flexible, often equipped with numerous sensory bristles and strong rasping ridges around the mouth. The last segment includes the anus and tubercle, which projects dorsally.