Shell intermediate in size between the smaller A. sportella and the usually larger Haplotrema vancouverense. It bears the beaded colabral riblets of A. sportella except that these become obsolete on the last whorl and the surface is marked by minute, close, wavy spiral striae.
Medium-sized (maximum mature width, 18–27 mm); growth determinate; depressed-heliciform; moderately thick-walled; ± opaque. Whorls: ca 6; evenly increasing in width, more rapidly before mature lip; spire whorls slightly convex. Spire: low, domed; apex flattened. Suture: moderately indented. Last whorl: descending to the peristome; no crest behind palatal lip. Periphery: rounded, medial. Protoconch: smooth. Teleoconch sculpture: ± evenly spaced and sized colabral riblets, becoming obsolete on the last or penultimate whorl; microscopic spiral striae that cut tops of colabral riblets into beads. Periostracum: cuticular. Umbilicus: ca 1/4 of w; wide, open and not occluded by the columellar lip. Aperture: subovate (wider than high). Peristome: incomplete. Apertural dentition: none. Palatal and baso-columellar lip: narrowly expanded, thin-edged. Peristome, viewed from side: prosocline, strongly arched; forward-directed portion on between periphery and suture strongly down-turned. Parietal callus: glazed, transparent. Colour (periostracum): dark straw yellow, slightly shining; shell grey-white under periostracum; aperture and lip milky whitish.
Long, slender; cream-coloured, with dorsum, head and tentacles darker; mantle with fine, pale brown speckling.