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DescriptionFilograna implexa has a translucent, pinkish-grey body up to 0.4-0.5 cm in length. It forms a thin, translucent white tube marked by thin growth rings from which it extends its tentacles and is normally found in colonies of large numbers. The body has up to 35 chaetae-bearing segments divided into a membrane-covered thoracic region of 6-9 segments and abdominal region. An unsegmented region that does not have chaetae separates the thorax and abdomen. The abdominal chaetae are smaller than the thoracic which develop a sickle-shaped towards the posterior end. Each segment also bears a pair of small, toothed, rasp-shaped plates (uncini) attached to the parapoda that are smaller in the abdominal region than in the thoracic region. The head bears two eyes and has two lobes each bearing four colourless, white or pinkish pinnate tentacles. Two of the eight tentacles, one on each side have a distinctive pale yellow, cup-shaped operculum. The base of the tentacles is surrounded by a toothed collar that has finely serrated chaetae and is notched on the ventral surface.Filograna implexus is a filter-feeder. Individuals are gonochoristic and reproduce via a pelagic larval stage throughout July, August and September. Filograna implexus also reproduces by asexual budding. This species can be mistaken for Salmacina dysteri which lacks the distinctive cup-shaped operculum.