« Protoconch planispiral, of about 2 whorls, smooth and transparent, with a slight collabral rim separating it from the teleoconch. Tube subcylindrical, slightly curved and crossed by 20-25 raised rings with interspaces as large as the rings. Longitudinal microsculpture crossing the entire tube both on the rings and the interspaces. Septum discoidal and usually quite low under the cutting plane with traces of temporary septum. Aperture perfectly circular, with a swelling, crossed by 4-5 rings, at the beginning slightly contracted, then enlarging and forming a small and sharp edge. Operculum corneous, light brown; external surface crossed by 3-4 concentric small rings; the internal surface, in profile, stair-like shaped (3 steps), showing a sunken nucleus. Colour dark brown in fresh specimens with periostracum, white in the beached ones. » – Pizzini & al.: “The family Caecidae in the South-West Pacific (Gastropoda: Rissooidea)”, Bollettino Malacologico vol. 49, Milano 2013, p.7. The rings are much more pronounced than in trachea, and the tube is more slender.
 
« C. sepimentum has a temporary septum, which is somewhat different from the definitive one, being more protruding and dome-shaped, quite similar to that of C. vertebrale. » – Ibid.