Shell: Shell large, solid, turreted , comprising 10 to 12 flat-sided to weakly-inflated whorls and reaching 57 mm in length. Protoconch unknown. Early whorls sculptured with dominant axial ribs, but later developing spiral cords and becoming more cancellate. Adult shells sculptured with broad, subsutural, flattened spiral cord and four or five smaller spiral cords diminishing in size abapically, and with weak axial ribs and incised lines, stronger in early whorls, becoming progressively weaker and narrower abapically, presenting overall smooth, tesselate appearance. Several varices randomly distributed. Suture distinct, slightly inset into each successive anterior whorl. Body whorl very large with strong varix opposite circular, flaring outer lip. Shell base weakly constricted, sculptured with numerous spiral cords and weak, colabral, axial striae. Aperture large, circularovate, with concave columella having weak callus. Outer lip of aperture thick, smooth, circular, fusing with anterior canal to form complete peristome. Anterior canal centrally located, tubular, projecting through shell base. Anal canal weakly defined. Shell color dark- to light-brown. Aperture tan with shiny brown and whitish patches on columella and outer lip. Operculum corneous, circular, multispiral with central nucleus and ragged, transparent edge. Anatomy: Animal essentially same as other Terebralia species. Head-foot blackish, snout mostly black with some cream-colored blotches, upper foot gray, sole white. Tentacular peduncles thick and long; tentacle tips narrow, short. Inhalant siphon thick, fringed at edge; internally, with close-set papillae and with crescentic, lightly pigmented, slit-like, sunken sensory pit bordered with black pigment. Ridge-like osphradium very narrow, long. Ctenidium long, very wide, comprised of extremely shallow leaflets. Mantle tissue supporting ctenidium very thin. Rectum large, wide. Style sac extremely long, extending from stomach anteriory to pericardium. Kidney bright green. Female pallial oviduct with wide medial fusion. Male pallial gonoduct comprising two simple laminae.

The shell of Terebralia semistriata closely resembles that of Terebralia sulcata, but is much larger and heavier, has weaker sutures, is weakly sculptured with flattened spiral cords and, except in juveniles, lacks axial ribs. The peristome is complete in adults. This species lacks the sculptural variability seen in the other two Terebralia species.

Distribution: Terebralia semistriata has the most limited distribution of any Terebralia species, and appears to be confined to tropical Australia and the southern coast of New Guinea. Although its developmental biology is unknown, its limited distribution suggests that this species might have direct development.
Ecology: This species was observed on the surface of open mudflats off the breakwater at Cairns, Queensland, and in the center of the mangroves at Magnetic Island, Queensland. In both places it was found on soft, sticky, cohesive mud.