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The prostomium is often rounded and truncate, but may be pointed or have a pair of lateral horns. A pair of highly mobile, grooved tentacular feeding palps which arise from the peristomium is always present; they are often lost in preserved specimens. A median antenna may also be present. The prostomium is elongated posteriorly and bears paired nuchal organs. The parapodia are biramous, except for the first segment which may lack notochaetae in some taxa. Dorsal and ventral cirri are absent. Branchiae are often present, either restricted to a few anterior segments or present on most segments; they are located on the dorsum adjacent to the notopodial lobes to which they may be partially or completely fused. Branchiae are usually some-what flattened, and may be simple and laterally ciliated, or may carry pinnae or lamellae. Other structures also referred to as branchiae may occur ventrally (in Lindaspio, not known from Australia) or as accessory structures on notopodia (in Dispio species). The pygidium may have paired elongate anal cirri, or more numerous and smaller cirri and/or lobes. Aciculae are absent. Notochaetae and neurochaetae include simple capillaries, either smooth or limbate, and simple hooks with apical teeth; compound chaetae are absent. Both hooks and capillaries may be sheathed, the latter in some taxa as stout sabre chaetae in ventral neuropodial positions. Other chaetal types present include recurved hooks and modified spines. In many spionids, all segments are similar, but in Polydora and related genera (informally but widely known as polydorids), the fifth segment is modified and carries one or several additional types of chaetae including simple spines, stout brush-tipped and terminally cuspate spines, and more slender accessory chaetae.
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