This species represents one of the largest and most robust gastropods inhabiting the southwestern Atlantic shelf. It possesses an exceptionally heavy, thick shell with an ovate-fusiform outline, reaching maximum recorded lengths between 150 and 200 mm. The outer surface exhibits a dull, pale yellowish-cream to light brown base coloration, which is typically covered by a thin, greyish periostracum in living specimens. The shell features a remarkably short spire and a smooth, rounded protoconch lacking prominent ribs or sculpture. The aperture is strikingly wide, showcasing a smooth, polished interior with soft tones of peachy-orange or salmon, and it lacks an operculum in adult stages, meaning the animal relies entirely on retracting its soft body deep within the shell for defense.

Geographical distribution: This marine mollusk is native to the temperate and warm-temperate waters of the Southwestern Atlantic Ocean. Its northernmost range begins along the coastal shelf of Rio de Janeiro, Brazil, extending continuously southward along the entire coast of Uruguay. The southern limit of its distribution reaches the colder waters of northern Patagonia, specifically terminating in the San Matías Gulf in the province of Río Negro, Argentina.

Habitat: It is restricted to benthic marine environments of the continental shelf, specifically preferring soft, unconsolidated substrates. The species thrives in areas characterized by fine sand, mud, and clay-rich sediments within the subtidal zone. Its depth distribution is quite broad, ranging from shallow coastal waters as close as 5 meters deep down to offshore benthic zones reaching depths of approximately 70 meters, where bottom currents are calmer and temperatures remain relatively stable.

Feeding: It is an active, carnivorous predator and opportunistic scavenger within its benthic food web. Its diet mainly comprises other soft-bottom invertebrates, with a strong preference for medium to small-sized bivalves and other gastropods sharing its habitat. To capture its prey, it utilizes its highly developed, expandable muscular foot to completely envelop and suffocate the victim, or to apply steady pressure until bivalve shells open, allowing the insertion of its proboscis to consume the soft tissues using its specialized radula.

Behavior: This is a solitary organism that moves slowly across the ocean floor via muscular waves generated by its broad ventral foot. It displays semi-infaunal behavior, frequently burying itself in the soft sandy sediment with only its siphonal canal exposed to ensure a continuous intake of oxygenated water. This burrowing habit serves as an effective defense mechanism against large predatory demersal fish and also functions as an ambush strategy, allowing the snail to detect prey through highly sensitive chemoreceptors that pick up chemical trails in the surrounding water.

Reproduction: This species is dioecious, with separate sexes and internal fertilization. Its reproductive strategy is characterized by direct development, completely lacking a free-swimming planktonic larval stage. After mating, the female produces large, free-floating, translucent ovigerous capsules that are spherical and gelatinous, ranging from 5 to 8 cm in diameter. Unlike many other volutes, these egg capsules are unattached and drift freely along the seabed with the bottom currents. Each capsule contains a dense, nutrient-rich fluid that feeds a variable number of embryos, which complete their entire development inside the protective membrane, eventually hatching as fully formed miniature crawling juveniles.

Conservation status: Pachycymbiola brasiliana has not been formally evaluated for the IUCN Red List of Threatened Species, leaving its global status unclassified. However, local populations face severe pressure from anthropogenic activities, particularly as bycatch in commercial bottom-trawling fisheries that disturb benthic habitats. Additionally, localized harvesting for the ornamental shell trade and human consumption in several South American coastal regions represents a constant pressure that could jeopardize the long-term viability of local populations.