No recorded weight measurements for Pecos assiminea are available at this time.

Pecos assiminea (Assiminea pecos) is a very small golden snail found in a few locations of the Pecos River Basin in New Mexico and Texas. Snails in the Assiminea genus are primarily marine and usually associated with the sea, Pecos assiminea is found the furthest inland of all these species.   

The shell of Pecos assiminea is chestnut color and nearly translucent.  

Sounds have not been identified or recorded for Pecos assiminea. 

Pecos assiminea range from 1.36 to 2.16 millimeters (0.05 to 0.08 inches) in shell length, with females being larger than males. Their shell has a broad, oval opening and is regularly conical, with up to 4.5 strongly incised whorls. The genus Assiminea does not have tentacles and their eyes are in the tips of short stalks.

A population of snails along the Río Monclova in Coahuila, Mexico, were initially reported to be Pecos assiminea. They have since been described as a separate species, Assiminea cienegensis, which are genetically distinct and have a smaller and broader shell. 
 

Individual Pecos assiminea snails are strictly male or female. Fertilization is internal, and females likely deposit eggs in gelatinous masses in their habitat where they develop into larvae. Little is known about specific development details in this species, other gastropods may reach sexual maturity in as few as six months. The seasonality, frequency of breeding, fecundity, or other aspects of reproduction are also unknown. Fluctuating surface water levels and winter freezing of inundated areas appear to be limiting factors influencing population size and individual mortality. 

The lifespan of Pecos assiminea has not been recorded. 

Breeding habitat specifics or associated behavior has not been studied for this species. 

Pecos assiminea is closely associated with permanent spring run wetland habitats, where they live in saturated mud with plant communities that are dominated by species like saltgrass (Distichlis spicata), chairmaker’s bulrush (Schoenoplectus americanus), common reed (Phragmites australis), spike rushes (Eleocharis spp.) and rushes (Juncus spp.). They are typically near the surface of the soil beneath mats of vegetation and plant litter, and may also rarely occur in the water of aquatic habitats. A balanced amount of vegetation litter is an important habitat component that provides food, shade, cover and maintains microhabitat temperature and moisture.

Pecos assiminea have a radula, an organ of tiny teeth, that they use to scrape food off of surfaces and into their mouth. They likely forage on the bacteria, detritus, fungi and algae found on live and dead vegetation and coarse organic matter. They may also incidentally consume small invertebrates as they feed.  

Pecos assiminea respire by breathing air directly. They commonly maintain an air bubble in their mantle cavity, and have gills that are vestigial, or remnant, and not likely used for primary respiration. Pecos assiminea are presumably nocturnal and most active at night, which is similar to their neighboring gastropods.