Snail pronunciation: luó sī.

Snail (scientific name: Margarya melanioides): an animal of the family Conchidae, the snail genus. It is a freshwater-born mollusk with an operculum and shell. The shell is large, more than 100 millimeters high. The shape is conical or tower-conical; thick, greenish-brown or brown. Most have seven conchae, including two protoconch ribs, with spiny or papillate projections on the shell surface, or only smooth conch ribs. Operculum a horny sheet. Dioecious, male right antennae short and thick, forming mating organ.

Ovoviviparous, with 3-7 embryonic snails in each 1 brood sac, and a shell height of 10 millimeters or more. Lives on the bottom of lakes and spreads throughout the lake bed. Lives in deeper water and shallow water. The snail creeps to the bottom of the lake with a broad foot. Feeds mainly on diatoms growing on the lake bottom and debris in the mud. It is endemic to China, distributed in the highland lakes of southwest China, and found in Dianchi, Erhai, Fuxian Lake, Isolong Lake and Datun Lake.

Morphological features

The snail is the type species of the genus Screw. It is a freshwater-born species with a screw operculum. The shells are large, conical, up to 100 millimeters in height, thick, greenish-brown or brown. Most have seven conchae, including two protoconch prongs, and each conch has a well-developed oblique shoulder on the upper part of the conch, except for the protoconch prongs.

Verticillasters mostly with three, rarely four, strongly spiraled ribs, the first spiraled ribs decreasing in the shoulder of the spiral, with a row of spiraled, small, regular nodules on the early verticillaster ribs, and obtuse, large nodules on the last two verticillaster ribs. The second prong at the edge of the whorl is the most developed, with regular prominent nodules on the early whorls and spines or large, irregular nodules or wavy projections on the last two whorls.