Type material: Holotype (121.4mm wide) deposited at Paris National Museum of Natural History, France with Registration No: MNHN-IM-2000-38134. Other material: Paratype 1 (124.6mm) in H. Dekker collection; Paratype 2 (92.0mm), Paratype 3 (96.4mm), Paratype 4 (97.2mm) and Paratype 5 (104.3mm) in Dr Thach collection. All types from type locality. All sizes including spines.
Diagnosis: The new species is characterized by very large size, white apex, angulate rim of umbilicus and two brown spiral bands at the middle of lower side. Description: Shell large for the genus with width range 92.0-124.6mm of collected specimens. Spire tall, sutures deeply channeled. Body whorl rough at upper side and moderately inflated. Holotype width (including spines) reaches 384.8% of height and equal to 205.2% of height if not including spines. Average width of body whorl of holotype (not including spines) occupying 53.3% of that of holotype if including spines. Sculpture consists of many undulate radial ribs bearing rounded granules arranged into spiral rows at upper side and fine, closely-spaced radial riblets at lower side. Aperture ovate, nacreous and occupying 79.1% of holotype height, outer lip slightly thick and steeply descending. Lower side slightly inflated with broad, nacreous band bordering the umbilicus. Columella curved and narrow, umbilicus wide and deep with angulated rim and lateral sides parallel to shell axis. Color copper red at upper side and pinkish white at lower one.
Etymology: The new species is named in honor of Henk Dekker from The Netherlands for his interest at Vietnamese shells.

The new species differs from all species of genus Guildfordia Gray, 1850. Guildfordia delicata Habe & Okutani (1983) is not accepted in MolluscaBase. The new species differs mainly from Guidfordia yoka Jousseaume, 1889 as follows: (1) spire narrower and less inflated, (2) axial ribs at lateral side much weaker, (3) aperture more descending at frontal view, (4) columella less curved, (5) sutures much deeper with sharply angulated rim, (6) granules less numerous along periphery of body whorl at upper side, (7) radial ribs at upper side undulate, not curved nor rectilinear, (8) umbilicus much deeper with purple-red sides and angulated rim, (9) base of spines having different shape at lower side, (10) redder spiral bands, (11) different localities, Vietnam versus Japan. Another congener of the new species is Guildfordia superba Poppe, Tagaro & H. Dekker, 2005 which is distinguished mainly from the new species by: (1) smaller adult size, 77.0-81.1mm with spines, after Poppe et al. (2005) versus 92.0-124.6mm in width with spines, (2) spines straighter and less curved apically, (3) body whorl flatter, (4) spire broader, (5) more numerous granules at upper side, (6) sutures shallower, (7) aperture more elongate, (8) different colors of apex, (9) different localities, Philippines versus Vietnam.

Type locality: off Nha Trang area, Khanh Hoa Province, Central Vietnam.
Habitat: Sandy bottom at 120-180m.