The family Rissoellidae M.E. Gray, 1850 is made up of species with the shell small, oval-conoid, thin, smooth, transparent-vitreous, often iridescent with the spire more or less raised, with convex whorls, the last of which is rather swollen, with an obtuse apex, a thin sharp peristoma, a narrow umbilicus, sometimes only a slit. From the above, clearly distinctive features from many microspecies of the family Rissoidae do not appear. But there are both morphological and anatomical characteristics which clearly differentiate the species of the family Rissoellidae from those of the family Rissoidae: above all, the presence of 4 cephalic tentacles, two real tentacles and two protuberances, in between the tentacles, and of the same length.
Then the shape of the operculum, semicircular with acuminate apophysis and having, on the inside, in the centre, a sort of rudimentary rostrum (more or less pronounced). But, a notable distinction, the Rissoellidae show some Prosobranch characteristics (protoconch not heterostrophic, a simple foot, type of reproductive system, eggs in capsules) together with characteristics atypical to that subclass (2 pairs of tentacles, eyes placed in the centre of the tentacles, renal organ invading the top of the mantle, conformation of the operculum, etc), so this family has sometimes been considered to belong to the Prosobranchs - Thiele (1929), Fretter (1956), Fretter & Graham (1962), Nordsieck (1972), Golikov & Star-obogatov (1975) and sometimes to the Opisthobranchs -Fretter & Graham (1954).

Rissoellidae is a rather small family of gastropods with less than 30 named species worldwide. All rissoellids are found under 1 genus, Rissoella, and 5 subgenera. Subgenera were created based primarily on radular features (Ponder and De Keyzer 1998e). In the Gulf of Mexico there are only 8 known species (Rosenberg et al. 2009). Shells of rissoellids are typically less than 5 mm (1/5 inch) in total length and smooth and fragile. Shell shape is globose to ovate-conic, and the whorls are convex. The body whorl is large; the aperture is wide, ovate, and simple (Ponder and De Keyzer 1998e). The operculum is a half-moon shape, and the nucleus has a blunt internal peg at the apex. Typically, rissoellids feed on diatoms and algae, but some feed on detritus. Jaws of rissoellids are paired, and the radular teeth show considerable diversity between subgenera. Paired lateral teeth are present, marginal teeth may or may not be present, and radular teeth may or may not be asymmetrical (Ponder and De Keyzer 1998e). A crystalline style is absent, but a gastric shield in the stomach is present. Rissoellids are usually located in lower littoral and sublittoral regions worldwide (Ponder and De Keyzer 1998e). In Texas Rissoellidae is represented by 2 species whose size ranges from 750 µm to 1.5 mm

The following key is proposed for the Mediterranean species of the family Rissoellidae, to be applied to adult specimens in good condition of freshness:
1. a Shell with rather elongated spire (turriculated) R. diaphana
b Not turriculated shell (globose ovate) (2)
2. a Shell with rather squat spire, valvatiform, umbilicus evident, deep and round R.
globularis
b Ovate conical shell, rissoiform (3)
3. a Body whorl very globose, umbilical slit narrow, pink-opaline colouring (also in worn
specimens) ... R. opalina
b Body whorl less globose, spire slightly higher, umbilical slit more open, showing the
internal "naticiform" structure, whitish colouring, vitreous ... R. inflata