Shell: Shell elongate, thick, solid and turreted, comprising as many as 20 flat-sided whorls and reaching a length of 190 mm. Pro-toconch unknown. Early whorls sculptured with strong, colabral axial ribs; spiral incised lines appearing on ninth or tenth whorl, gradually increasing to three in number. Adult whorls sculptured with four equal-sized, flattened spiral cords, three deep spiral grooves, and overlain by broad axial ribs, producing weak, square nodules. Varices broad, prominent and randomly distributed. Suture deeply impressed. Body whorl large, wide, with large varix opposite outer lip of aperture. Shell base moderately constricted, sculptured with many small spiral cords and numerous, very small, weak axial striae. Aperture ovate, grooved within; columella concave with thick callus and weak plait at anal canal; outer lip sinuous and flaring at anal canal , sweeping in broad arc to anterior canal, although not joining it. Anterior siphonal canal short, tubular and nearly closed at junction of outer lip. Columellar pillar with two internal folds. Palatal tooth opposite each external varix. Shell brown to bluish-black, occasionally with wide lighter bands; aperture glossy brown, columella light tan. Operculum corneous, circular, multispiral with central nucleus, transparent and tattered at edge.
External Anatomy: Head-foot dark brown; snout and tips of cephalic tentacles black. Head with muscular, broad, transversely-lined snout, and with broad cephalic tentacles, each bearing large eye at peduncular base. Foot large, having white sole and large anterior mucous gland extending around anterior half of sole periphery. Dorsal surface of foot (mesopodium) deeply grooved, conforming to heavy columellar plaits of shell. Ciliated groove on right side of foot in females, emerging from anterior pallial oviduct and leading to very large, bulbous, white ovipositor near base of foot; ciliated groove at posterior end of ovipositor opening into large, cylindrical, jelly-producing chamber in inner right part of foot, beneath ovipositor. Inner ovipositor chamber filled with plug of tissue arising from posterior wall of chamber; chamber extending posteriorly, terminating under operculum. Mantle green; mantle edge bifurcate with scalloped outer fringe and inner row of 15-20 papillae. Inhalant siphon marked by indentation. Papillae at inhalant siphon white-tipped. Inhalant siphon thick, muscular, with black undersurface at edge; inner surface of inhalant siphon with black-pigmented area surrounded by yellowish ring and with white, deep, semicircular light-sensitive pit, bordered with transverse ridge. Light-sensitive pit with white, villous epithelium comprising many small indentations and tiny pits, underlain by large vacuolated cells over layer of darkly pigmented cells, and forming pigment cup. Sensory area of inhalant siphon innervated by extension of left mantle nerve. Exhalant siphon black, bulging beyond mantle edge.
Terebralia palustris is by far the largest prosobranch found in the mangroves, and, for a potamidid, it can attain a truly remarkable shell size: Benthem Jutting (1956) cited a shell 160 mm long from Java, but an even greater giant of 190 mm in length has been recorded from Arnhem Land, Australia (Loch, 1987:4). Loch (1987:4) hypothesized that gigantic specimens were the result of parasitic castration, suggesting that in animals with destroyed gonads, the energy normally directed to reproduction is diverted to growth. Terebralia palustris has a shell three to four times the size of Terebralia sulcata, and about twice the size of large Terebralia semistriata. The only other mangrove snail that approaches it in size is Telescopium telescopium.
Aside from its large size, there is nothing unusual about the shell except that in longi-tudinal section there are two columellar plaits, a strong central one and a weaker parietal one. Opposite these, on the inner shell wall, there are palatal folds wherever an external varix has been formed. An excellent depiction of these folds in cut shells of Terebralia palustris and Terebralia sulcata has been presented by Martens (1897, pl. 9, figs. 24, 27). According to Tryon (1882:250), this character was discovered by Brot, and does not occur in other potamidids. Juvenile shells are quickly eroded and partly dissolved in the very acidic environment of the mangroves; shells with extant protoconchs were not found during this study.

This large, conspicuous species occurs in great numbers in brackish water on coastal mudflats in mangrove regions, where it appears to prefer fine mud substrates (Wells, 1980:1-2). Ecological studies have been conducted in the Nicobar Islands (Sewell, 1924), the Andaman Islands (Rao, 1938), Java (Soemodihardjo & Kastoro, 1977), Okinawa (Nishihira, 1983), Thailand (Shokita et al., 1984), and in northwestern Australia (Wells, 1980, 1986). I observed a large population of Terebralia palustris in the mangroves of Magnetic Island, Queensland, Australia, where it is sympatric with Terebralia semistriata and Telescopium telescopium. The adult population was restricted to the higher, seaward portion of the mangrove forest on a substrate of fine silty sand adjacent to a sandbar, and although very few individuals were found on open flats, they were abundant at tidal channels, where they appeared to have been washed out. Few young snails occurred in the open flats, but were common around mangrove roots. Segregation of juveniles, which inhabit intertidal channels and pools, from adults, which migrate into upper intertidal mangroves, was noted in New Caledonian populations by Plaziat (1984:122). In some areas, adult densities as high as 150/m2 have been recorded (Plaziat, 1984:136).
Terebralia palustris can tolerate considerable environmental stresses. Rao (1938:203) showed that it can live without food for a considerable period (as long as four months), and Soemodihardjo & Kastoro (1977) found that it can live out of water and without food for as long as three months.
As is the case with large adults of Telescopium telescopium, it is unlikely that many predators can successfully attack and eat adult individuals of Terebralia palustris, although the mud crab, Scylla serrata (Forsk&l, 1775), common in Indo-Pacific mangrove forests, is large and strong enough to crush the largest potamidids. Crushed Terebralia shells were observed around the mouths of burrows of these crabs in northern Australia (David Reid, pers. comm.). I did not see any empty shells with peeled apertures indicative of crab predation in Magnetic Island, Queensland, Australia. It is assumed that mortality due to predation occurs mainly in juveniles, but this has not been observed. Another predator of Terebralia palustris is man. Tryon (1882:250) remarked that.. in the Eastern Archipelago this species is assiduously collected by the natives, who roast them and suck the contents of the shell through an aperture made by breaking off the tip of the spire." This species is also eaten by Australian aborigines in Arnhem Land (Loch, 1987).

This species has the widest range of any Terebralia species. In the tropical Western Pacific, it occurs from the Ryukyus south through the Philippines, Borneo and New Guinea and throughout tropical Australia. It extends eastward to Palau and southeast to the New Hebrides [fide Oost-inqh, 1925) and to New Caledonia. Old records citing the Gambier Islands in Polynesia (Oostingh, 1925:49) probably refer to Pseudovertagus clava (Gmelin, 1791), which resembles Terebralia palustris in size and superficially in sculpture. Terebralia palustris occurs in mangrove habitats throughout the Indonesian archipelago and in the estuaries of Southeast Asia, west to India and Ceylon. In the Indian Ocean, it is found in Nicobar and Andaman Islands, the Maldives, Mauritius, the Seychelles, the Amirantes and Madagascar (Oostingh, 1925:49). Populations in east¬ern Africa occur from South Africa northward to the Red Sea.