Medium-sized to large, fairly high-spired cone-shaped shell with moderately wide umbilicus; whorls on upper side gemmate and inflated on both sides; two spiral grooves below suture (midrib-area divided equally); basal field often with 4-6 weakly developed spiral grooves; proxumbical rib never clearly separated in larger specimens. Subsutural rib whitish with irregular brown blotches; midribs light-brown or bluish-grey and mottled with brown; basal field with 5-6 dotted lines; umbilical crenae whitish with brown pattern (darkest area of base). Protoconch diameter 1.00-1.22 mm.
Medium-sized to large, diameter of specimens in collections usually 17-34 at 4 3/4 to 6 3/4 whorls. Shape: fairly high-spired cone-shaped, with whorls inflated; umbilicus moderately wide (UD ca. 16.5% of SD). Sculpture: Upper side: SSR distinctly separated; UMR and LMR of about equal strength; Periphery: PR strong, with UPR almost as prominent as LPR; UPR usually wider than LPR, similar to MR (often one ± fine additional spiral rib between the two); upper point of whorl attachment on central to upper part of LPR (therefore upper edge of LPR ± visible in suture); upper side and periphery crossed by deeply incised oblique axial grooves, resulting in a general gemmate appearance on early whorls, becoming almost smooth on body whorl of larger specimens; Base: IPR strong; BF of larger specimens without distinct spiral ribs, but often with 4-6 weakly developed spiral grooves; younger specimens with 5-6 ± smooth, faintly separated spiral ribs, crossed by radial plications, stronger towards umbilicus; wide PUR not or only weakly separated from BF; one wide, distinctly separated, irregular nodulose spiral rib (UC) surrounding umbilicus; columellar wall forming almost straight inner lip with plications for support of the columellar muscle, with deepest groove in UC overhanging umbilicus; no spiral sculpture on umbilical side of wall. Coloration: SSR and PR whitish with ± irregular brown blotches (about 10-16 on 4th whorl of UPR, each 1-2 nodules wide); MR light-brown or bluish-grey, ± weakly mottled with brown; BF light-brown or bluish-grey with 5-6 dotted or ± solid spiral lines (marking the reduced spiral ribs of the BF), wider towards the umbilicus; UC whitish with light- to dark-brown pattern (darkest area of base). - Protoconch: medium-sized to large (1.00-1.22, x = 1.11, sd = 0.057, n = 43; Recent specimens only); distinctly heterostrophic, some specimens with weak anal keel; whitish to light-brown, some specimens with outer corner in front of varix brown. - Operculum: as described for genus. - Radula and Anatomy: not known.

Architectonica karsteni differs from all other species in this genus by not having a distinctly separated proxumbical rib on the body whorl of the teleoconch, the umbilical crenae forming the only obvious spiral rib around the umbilicus. The single sympatric congener, A, nobilis, can be distinguished by its multi-ribbed basal field on the body whorl of adult specimens (only juvenile A. karsteni specimens show occasionally faint spiral grooves on the basal field), by midribs that are more coarsely sculptured and much narrower, and by a lower-spired shell with less inflated whorls.

Geographical distribution: Eastern Pacific, continental shelf (from Baja California to Peru) and Galapagos Islands. Habitat: Sublittoral (depth records between 18 and 183 m), most live records from below 50 m; muddy, sandy and rocky substrates.