What is "nacella"

Nacella is a southern, cold-water genus of true limpets, marine gastropod molluscs in the family Patellidae, the true limpets.

These limpets are found in the littoral zone and sublittoral zone of Antarctic and sub-Antarctic waters including ( Tierra del Fuego, Macquarie Island, Kerguelen Island, and Heard and McDonald Islands). The grayish-brown shell is suboval and flattened and the ribbing on the shell is rather flat. The shiny interior of the shell is rust-colored or chocolate-brown.