Description. — Shell almost cylindrical, very fragile and very small, with strongly convex and low whorls. Protoconch with one whorl and a diameter of about 150-160 µm, having a relatively large nucleus, about 40 µm in diameter. Teleoconch with tall spire with very convex whorls that increase slowly in height (D/H ~ 1.85 in average), the last whorl very rounded at the periphery. Suture deep. There is no shoulder or any separation of the whorls into two parts. The spiral furrows are slight and are formed by more or less elongate oval depressions, about 14-17 per whorl. Under high magnification it can be seen that the growth lines are opisthocyrt, being curved with a subsutural zone which corresponds to a concavity of the free border of the aperture in the middle-high part of the free border. Aperture almost circular. An umbilical fissure is almost closed by the reflected part of the columella. Dimensions: the holotype is 1.5 mm high.
Distribution. — So far only known from the type locality.
Etymology. — The specific name alludes to the lack of separation between the upper and the lower parts of the teleo-conch whorls.
Remarks. — This species, the first in the genus Pseudoaclisina described in this work can be perfectly differentiated from those in the genus Murchisonella by the lack of separation between upper and lower parts of the whorls and the growth lines having a single curvature.
Only the Murchisonella species from the East Atlantic and Mediterranean (M. atlantica and M. mediterranea) seem to be similar at first glance, but under magnification it is evident that they have the two areas of the whorls separated over most of the teleoconch and have a double curvature or inflection in the growth lines.
For the differentiation from other species in this genus see remarks in P. planicula spec, nov., P. micrometrica spec, nov., P. multistriata spec, nov., and P. rarisulcata spec. nov.