Paracrostoma armata: Shell relatively small, conical to oval, not more than three rather flattened whorls; one to three spiral cords supporting a spiral row of sometimes spiny nodules.
Shell: Relatively small, oval to conical, up to three flattened to slightly convex whorls, tip eroded. One to three spiral cords, especially upper ones supporting spiral rows of spiny nodules; on body whorl often addi¬tional cord visible. Some shells almost smooth. Aperture broadly ovate, large compared to shell, basal margin produced. Size: H = 26-38 mm, B = 18-24 mm.
Embryonic Shell: Smooth except for axial growth lines, sharp transition between apical area and penultimate whorl after about half of first whorl. Size of juveniles kept in brood pouch: 2.0-2.5 mm, 2.5 whorls.
Operculum: Oval, up to four whorls that increase in diameter, subcentral nucleus.
Radula : Length of ribbon: m = 18.4 mm (sd = 4.4 mm; n = 15), up to 180 rows of teeth. Central tooth with elongated main cusp and two or three much smaller accessory denticles on each side that taper in size; glabella narrow with straight lateral margins, rounded posterior rim that does not reach the basal rim of central tooth. Laterals with broad main cusp flanked by one to two accessory denticles on each side. Inner and outer marginals with large, broad outer cusp and spiny inner denticle.

Paracrostoma armata: Brotia binodosa with similar sculpture is more turreted and slender possessing more whorls. Both species deviate mainly in proportion of shell height to width (H/B), although not statistically significant. Brotia pseudosulcospira lacks spines, is larger with a darker, thicker, smoother shell.

Paracrostoma armata: Thailand: Prov. Phitsanulok: Endemic to Kaek River; only in middle course between Sakuno-thayan Falls (33 km E Phitsanulok) and Thung Salaeng Luang NP (90 km E Phitsanulok).