Arenicola brasiliensis (Nonato, 1958)
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)
Arenicola brasiliensis was long confused with A. cristata, which tends to live in quieter, muddier places. Arenicola brasiliensis extrudes earthworm-like coiled castings outside its burrow, while A. cristata castings leave a formless film or heap. The egg mass of Arenicola cristata has the appearance of a gelatinous streamer, while the eggs of Arenicola brasiliensis are firm and "egg-shaped". (Gosner 1978). The overall color of A. cristata tends to be greenish black, while the less robust A. brasiliensis is pinkish tan (Pollock 1998). Pollock suggests that A. brasiliensis might simply be a smaller growth form of A. cristatus (Pollack 1998). DNA sequencing (e.g., of the cytochrome oxidase I gene, a portion of which is widely used as a "bar code" for animals) of multiple representatives of these two putative species might clarify this question, but this has apparently not been done.
Arenicola lugworms are robust annelid worms, thickest in the front half, tapering toward the head and (more gradually) toward the rear. A 2 cm worm is about 9 mm wide and divided into 3 regions. The trunk has weak parapodia bearing bundles of setae and (starting roughly 1/3 of the way back) a tuft of gills on each side. The tail region lacks setae and parapodia. The small, contractile head lacks appendages but has an eversible proboscis armed with papillae. (Gosner 1978)
Arenicola brasiliensis may grow to 175 mm, with 17 segments bearing setae. It has 11 pairs of gills, on segments 7 to 17. (Morris et al. 1980)
Arenicola brasiliensis burrows in sand and mud in the low intertidal zone in bays (Morris et al. 1980).
The polychaete lugworm Arenicola brasiliensis is widely distributed, especially in warmer parts of the word (although it may be abundant in temperate regions as well, such as certain localities in San Francisco Bay, California, U.S.A.) (Kozloff 1993).
Arenicola brasiliensis is found along both coasts of North & South America, as well as in Hawaii, Japan, and Australia; it is broadly cosmopolitan in warmer seas (Morris et al. 1980).
According to Gosner (1978), on the Atlantic coast of North America A. brasiliensis is known only along the south shore of Cape Cod, but its range also includes Brazil and parts of the Pacific Ocean.
Arenicola lugworms feed on fine particles carried on currents pumped through their burrows (Gosner 1978).
Arenicola brasiliensis has separate males and females. After gametes (sperm and eggs) mature in the body cavity, they are discharged through six pairs of tubular ducts. Mature eggs are about 150 microns in diameter. In a study in Japan, spawning occured from July to September. Egg release may be stimulated by the presence of sperm in the water. Eggs are shed in the burrow, where fertilization occurs. A few hours after fertilization, the eggs are embedded in a firm jelly mass, just 2 to 5 cm in diameter but up to 15 cm long, extruded to the sand surface but remaining firmly rooted in the burrow by a tenacious stalk. Hatching occurs several days after fertilization and shortly thereafter the jelly mass breaks down, releasing the larvae. Larvae swim for a short time, then settle and begin to burrow. (Morris et al. 1980)
Evolution and Systematics
Systematics and Taxonomy
Arenicola brasiliensis may be referred to in some older literature by the junior synonym A. caroledna and has not always been distinguished from A. cristata (Morris et al. 1980).