The lugworm Arenicola brasiliensis (which for many years was not distinguished from the similar A. cristata) is a polychaete annelid worm in the family Arenicolidae. It is widely distributed, especially in warmer parts of the word. This worm digs a J- or L-shaped burrow and orients itself so that its posterior (rear) end is close to the surface. The anterior (head) end, which is kept well below the surface at the bottom of the J, ingests sand, creating a closed, funnel-shaped depression in the sand surface above the head. The worm swallows sand and mud, which adhere to mucus secreted on the everted (extended out of its body) proboscis. When the proboscis is inverted, the material sticking to it is pulled into the digestive system. Organic matter ingested with the sand is rapidly digested and the processed sand is periodically defecated at the surface near the tail end of the burrow in a distinctive long, coiled casting (the related A. cristata deposits fecal wastes in sandy sheets). The branched gills receive circulating blood, which contains hemoglobin. Gas exchange in the burrow is facilitated by pistonlike movements of the body, which stir the water and irrigate the burrow. Lugworms may reach densities as high as 50 per square meter and play an important role in turnover of organic matter in mudflats. (Morris et al. 1980; Kozloff 1993)
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