Alvania minuta
Alvania minuta is an extinct species of minute sea snail, a marine gastropod mollusc or micromollusk in the family Rissoidae.
Taxonomy
Alvania minuta is a homonym and has become a synonym of Pusillina tumidula.Description
The length of the shell attains 1.5 mm, its diameter 0.9 mm.The minute shell is oval, clathrate and imperforate.
The protoconch consists of 2 globose glossy whorls. The nucleus is minute, rapidly enlarging.
The teleoconch contains about 2 whorls, indistinctly shouldered just below the suture, then flatly convex. The body whorl is bluntly angled, its base almost flat.
The axial sculpture commences first, consisting of strong bluntly-rounded ribs, sloping forwards and reaching from suture to suture, the interstices narrower; they number about 19, and cease just below line of suture on the body whorl. The axials are crossed by much weaker spirals, indistinct on early whorls, 4 on penultimate whorl, broad and flatly rounded and cutting up axials into blunt laterally-elongate tubercles. A fifth spiral emerges from the suture-line on to base and is slightly crenulated by ends of axials. Below this are 2 smooth and much fainter ribs, the rest of base smooth.
The spire is a little higher than the aperture. The suture is much impressed. The aperture is slightly oblique, sub-ovate, angled above, effuse below. The peristome is discontinuous. The outer lip is thin, but does not appear to be finished. The arcuate columella is slightly oblique.