Shell: Shell moderately large, pendant-shaped, reaching 60 mm in length, and comprising about 12 weakly inflated to flat-sided whorls. Protoconch unknown. Early whorls highly cancellate. Adult shells with several wide, randomly placed varices, and sculptured with four or five flattened spiral cords and deeply incised spiral lines overlain by numerous axial ribs, forming overall sculpture of square nodules. Suture deeply incised. Body whorl wide, with expanded thickened outer lip. Aperture wide, ovate, slightly less than one-third the shell length, and with concave columella with broad columellar wash. Outer lip smooth to weakly crenulated, joining (fused to) base of columella just above short, centrally located, tubular siphonal canal. Body whorl sculptured with numerous beaded spiral cords. Shell dark brown, sometimes with lighter brown bands; varices whitish and beads sometimes light brown. Aperture shiny brown to cream. Operculum corneous, circular, multispiral with central nucleus and ragged edge.
External Anatomy: Animal (from Hong Kong) pigmented with yellow, dusky-brown blotches, flecked with bright yellow dots. Snout long, dark brown to black, with iridescent green, transverse stripes. Cephalic tentacles with broad peduncular bases and slender, long tips. Large black eye at anterior end of each peduncular base. Foot large, with deep groove on posterior propodium corresponding to columellar plait on shell. Sole furrowed with fine longitudinal folds. Opening to anterior pedal gland slit-like, extending posteriorly along two-thirds of sole edge. Females with deep ciliated groove leading from anterior pallial oviduct down right side of foot and around large, pad-like, bulbous, cream-colored ovipositor situated near medial foot edge. Small opening in ovipositor leading into glandular chamber inside foot (cross-hatched area). Gonads located in upper visceral coils; ovaries bright green (eggs and spawn masses also green); testis orange-brown. Kidney brown, one whorl long, comprising two lobes: large right lobe consisting of many fine lamellae; smaller left lobe with larger, coarser lamellae. Mantle skirt green, having bifurcate edge; outer (upper) edge scalloped; inner (lower) edge internally fringed with long, spade-shaped papillae having white tips; ventral mantle edge smooth. Deep indentation at mantle edge adjacent to inhalant siphon; exhalant siphon marked by minor indentation. Inhalant siphon thick, muscular, darkly pigmented along external edge, and with large, dark, inner papillae. Inner surface of inhalant siphon darkly pigmented with large, semicircular, unpigmented sensory pit innervated by a pallial nerve. In cross-section, sensory pit comprising thin layer of white Tissue underlain by dark pigment. Sensory pit located sev¬eral mm in front of osphradium and ctenidium.

Of all the mangrove snails described here, Terebralia sulcata has the thinnest shell, although it is by no means fragile. This shell is easily distinguished from that of Terebralia semistriata, its morphologically similar congener, by its smaller size, cancellate sculpture, and particularly by its prominent axial ribs. Shell size is very variable: some populations comprise only dwarfed individuals. Shell shape is also variable, especially between populations: shells can be very squat and wide or extremely tall and slender. Shell sculpture is highly variable, especially in the number and prominence of axial ribs. In some phenotypes the spiral cords are flat and the shell appears nearly smooth, sculpture consisting of incised spiral and axial lines; other phenotypes have strongly developed spiral cords and axial ribs and appear very cancellate. Juvenile snails have fine cancellate sculpture and deeply incised sutures. As in other Terebralia species, there are two plaits on the columellar pillar, extending up the entire shell, and opposite these, on the inner shell wall, there are teeth wherever an external varix has been formed. The shells of both Terebralia species are notable for the com-plete to nearly complete peristome, due to the fusion of the anterior outer lip to the anterior siphonal canal, and for the straight, short, tubular siphon, opening through the middle of the shell base. The complete peristome allows the animal to clamp down firmly on the substrate, and avoid desiccation and predators while maintaining communication with the external environment through the tubular siphon.

Terebralia sulcata is a hardy generalist able to tolerate desiccation and a wide range of substrate types, and is able to ingest roughly equal portions of algae and vascular
plants as well as large quantities of detritus and sand. In Hong Kong, Yipp (1980:705) identified four categories of plant materials, microalgae, filamentous algae, macroalgae and vascular plants, all of which underwent reduction on passage through the gut, with the possible exception of the filamentous algae.
In contrast to Terebralia palustris, which is a much larger snail and which occurs on fine mud substrates, Terebralia sulcata prefers coarser substrates and attains its highest densities on them. I observed a population of this species in a stand of dwarf mangroves in Hong Kong, a habitat that has been thoroughly described by Morton & Morton (1983: 222-223). This population, which also has been studied by Wells (1983) and Yipp (1980), occurs on intertidal sand and rocky habitats throughout the salt marsh and on the roots of the dwarf mangroves. Other Hong Kong populations of Terebralia sulcata occur in protected bays on similar substrates from which mangroves are absent (pers. obsr.; Wells, 1983:145). In contrast to the Hong Kong populations, Wells (1983:152) showed that this species is found only in mangroves in Western Australia and suggested that habitat segregation might differ in various regions. For instance, in the mangroves of the Bay of Rest, Western Australia, Wells (1980:2) found Terebralia sulcata was widely distributed throughout the seaward mangroves, Rhizophora stylosa and Avicennia marina, where it was common among the pneumatophores of the latter; however, in a mangrove forest in the Kimberly area, Western Australia, Terebralia sulcata was narrowly restricted to the floor of the Aegialitis zone (Wells & Slack-Smith, 1981). Wells (1986:88) remarked that of the mollusks living among Avicennia in the Bay of Rest, Western Australia, Terebralia sulcata dominated in terms of density and biomass, forming 50 percent of the total numbers and 85 percent of total biomass. Wells might not have discriminated Terebralia sulcata from Terebralia semistriata; consequently, his conclusions about habitat segregation might be erroneous and should be reconsidered. In Java, Benthem Jutting (1956:443) recorded this species living on mudflats, often attached to branches and roots of mangroves or on stones. It is likely that the microhabitat of this generalist species varies throughout its geographic range.
Little has been written about the predators of this SDecies. Wells (1986:88) has suggested that in the Bay of Rest, Western Australia, Terebralia sulcata commonly lives among Avicennia pneumatophores for protection from predatory rays, which are largely unable to feed among them. A small copepod lives in the mantle cavity of the Hong Kong populations.

The easternmost extension of this species in the Pacific Ocean is in the western Caroline Islands and in Guam (Roth, 1976: 8). Terebralia sulcata is common throughout the western Pacific from the Ryukyus south to Taiwan, China, Viet Nam, and throughout the Philippine archipelago. It also occurs in Borneo, New Guinea, and throughout tropical Australia. Terebralia sulcata is common throughout the Indonesian Archipelago, the Malayan peninsula, and in the estuaries and mangroves of Viet Nam, but according to Brandt (1974:195), has never been found alive in Thailand.