Habitat: it lives on sandy-muddy bottoms in the infra and circalittoral zones. It is often found in the gastral cavities of Astropecten auranciacus.
Distribution: common all over the Mediterranean
Notes: shell solid, whorls convex, broad suture. Roundish in aperture, lip thickened, with varices externally, denticulated internally. Surface crossed by axial ribs and spiral little cords originating a granulous sculpture fine and regular. Columellar callum adherent, brown-dark violaceous in colour, as well as the peristome. No stain, black in colour, at the base of canal. Ground light hazel-brown in colour, with bands either reddish or brown. Varices white in colour. Canal open. Operculum corneous, yellowish in colour. Juvenile specimens arc recognizable due to their colour patterns, to the fine sculpture granulous and to the reduced sizes of protoconch. It is distinguishable from its similar one N. incrassatus due to the characteristics listed under this species. Moreover N. pygmaeus lives in a deeper habitat and it has often a bigger number of varices (up to 6). Some varieties as: elongata, evaricosa B.D.D., 1882 , paucicostata Nordsieck, 1974, have no taxonomic value. The adult specimens average measures are around 7-8 mm in height.

Shell. As in T. reticulata British and Danish shells show different forms. The former are described first and the features in which Danish ones differ are noted later.
This resembles the shell of incrassata much more than that of reticulata both in size and ornament. The shell is glossy and shows no obvious periostracum; the spire is narrow (apical angle c. 40°); the sutures are wavy and lie distinctly below the periphery of the upper whorl; the basal spiral gutter is more open and shallower than in incrassata; the spiral ridges are fewer, 10-11 on the last whorl above the spiral gutter, 4-5 on the whorls of the spire, and are about equal in breadth to the intervening grooves; the boss below the gutter has 5-6 ridges; the costae arc narrower than the intervening grooves, are not flexuous on the last whorl, but prosocline throughout their length; the labial varix is narrower and lower than in incrassata; there are usually varices on some of the whorls of the spire; the interaction between costae and spiral ridges is both more localized and more intense than incrassata so that where they cross there is a smaller, squarer and rather more upstanding tubercle than in that species. The protoconch is smooth, has 2.25 whorls and measures 750-950 µm across. In Danish shells the spire is relatively shorter and broader, giving an apical angle of c. 50°. The whorls are less tumid so that the profile of the spire is flatter. The ornament is less marked though the labial varix is as well developed.
Aperture. Much as in incrassata. The edge of the outer lip is more regularly crenulated by the spiral ornament; internally it bears 9-10 teeth on a ridge-like thickening; the siphonal canal is more widely open, especially on the outer lip side; the inner lip does not spread far over the last whorl; it bears an adapical and 2-3 basal folds.
In Danish shells internal thickening of the outer lip is reduced, there are no teeth on the inner lip and its spread over the last whorl is minimal.
Colour. In general like the other species but the spiral banding is clearer; the pigment bands cross the varices (where developed); the labial varix is much less while than in incrassata; the inner lip and columellar area are pigmented; the siphonal canal is brown, but lacks the intense pigment spot of incrassata.
Size. Up to 14x8 mm, Danish specimens 9x5. Last whorl = 66% of total shell height; aperture = 40-45% of total shell height. British specimens, breadth = 57-58% of height, Danish specimens, 61%.
Animal. As in incrassata, but with a longer siphon, more marked lateral projections at the front end of the foot and with distinctly longer metapodial tentacles. Colour like a pale incrassata.
Geographical distribution. A southern form which extends north from the Mediterranean to the English Channel and along the west coasts of the British Isles to the Shetlands and Skagcrrak, Kattegat and Limfjord. Not found in thc North and Irish Seas.
Habitat. This is not a littoral species. It occurs on sandy bottoms from 1 to about 200m. It is not common. Food. Unknown; presumably another scavenger.