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DescriptionMagelona filiformis is a thin, thread-like segmented worm that reaches lengths of up to 8-10 cm and is either translucent, pink (mature females) or white (mature males). The body is divided into a head, 8-segmented thorax, abdomen of approximately 130 segments and a terminal pygidium. The head consists of a flattened, elongated, prostomium with small horns, a globular-shaped proboscis, a pair of palps and a long thin tentacle either side bearing two rows of papillae. The first segment adjacent to the head lacks chaetae or parapodia. Either side of the thoracic segments each bear foliose lobes dorsally, 15 dorsal chaetae and 10 ventral chaetae. The ninth chaetiger divides the thorax and abdomen, bears foliose lobes both dorsally and ventrally and is distinguished by the presence of 25-30 chaetae on both parapodia. Abdominal segments each bear widely-spaced foliose notopodial and neuropodial lobes with a short cirrus and row of horns and short rod-like dorsal and ventral lobes. Towards the posterior of the abdomen the neuropodia and notopodia are positioned increasingly to the posterior end of each segment. The most posterior end of the body is tapered into a pygidium bearing two anal cirri.