Perotrochus hirasei mm 66 Seashell Sea Snail Gastropod Top Shell Slit Snail

Perotrochus hirasei mm 66 Seashell Sea Snail Gastropod Trochoidal Slit Snail Top Shell, with Operculum, only a piece, as in photos.
Measures: diameter mm 66, height mm 57.
Family: Pleurotomariidae.
Common name: The Emperor's Slit Shell.
Syn. Mikadotrochus hirasei hirasei, Mikadotrochus hirasei yamamotoi, Perotrochus hirasei.

The Pleurotomarids or "slit snails", is a family that includes several hundred fossil forms, mostly Paleozoic. It is one of the oldest families of gastropods, from the Upper Cambrian onwards. After suffering a notable blow during the Cretaceous-Paleogene extinction event, in the Cenozoic they remained confined to the deeper waters. In 2009, a new study in the Journal of Paleontology described the first presence of Mesozoic pleurotomariids from Antarctica.
The first living specimens were dredged in 1879 in deep waters off the West Indies.
Currently this family is represented by a group of species that live only in deep waters (150-300 meters) such as benthos in the mesopelagic zone. They are preyed upon by crustaceans and fish, but are remarkably resistant to attack: when in danger they secrete a white liquid to repel predators. They feed mainly on sponges and supplement their diet with crinoids and octocorals; in aquariums they also feed on fish and clams.
The shell has a trochoidal shape, with a pearly interior. The navel is imperforate, having a deep fissure or sinus in the upper outer margin of the peristome, which serves for the exhalation phase of respiration. The fissure is gradually sealed behind the opening which advances as the size of the shell grows.