Shell relatively large for the genus, fragile, transparent. Protoconch: with about ¾ whorl; one relatively wide groove on the inner side of the whorl; groove with weak lamellae on the last half portion; one flattened, rather strong ridge on the outer side of the inner groove; one shallow groove at the outer side of the protoconch. Teleoconch: with about 1,5 whorls; one weak carina in the middle of the ventral side of the shell, and another one in the middle of the dorsal side; numerous, irregularly spaced, weak axial riblets on the teleoconch, intersected by numerous spiral lirae, being more numerous on the peripheral side of the shell; shell strongly angulate in apertural view; suture well-marked, deeply impressed. Aperture: subcircular; peristome continuous; inner and outer lips thin, the former attached to the previous whorl. Colour: transparent, yellowish-brown.
Shell-dimensions (in mm): 0.42-0.48 mm

Ammonicera tenuicostata sp. nov. is related to A. vangoethemi Sleurs, 1984, but differs from the latter in having a strongly angulate body-whorl, and by the presence of a weak carina on the ventral and dorsal sides of the shell; there are more numerous axial ribs and spiral lirae on the teleoconch of A. tenuicostata sp. nov.

Type-locality. — Republic of Maldives, North Male Atoll, Baros Island