Snails of the late Lentocene

The largest gastropod species is the lobed snail (Megadiscus lobatus), which has become heavier than an African giant snail, exceeding 1 kg of weight. The species have large lobes on the shell, producing a wavy appearance. Only geotters, which possess primordial durophagous adaptations, are able to ordinarily feast on lobed snails. 
They are giant helicids derived from the "domestic" snails brought by agricrows. After their arrival, helicids rapidly naturalized in Polarica and Weddell island, where they've partially replaced the autochthonous charopids, a family of snails that have persisted in Antarctica since the Holocene.
Highly specialized charopids had no trouble with the helicid invasion, like the glass spik (Spinidiscus vitreum), which has developed spiky concretions on the upper part of the shell.
The calcareous shell is reinforced by the presence of silica, becoming even harder and practically impossible to crush with teeth or beaks. Thanks to this, glass spiks have no natural predators, except for some species of birds that have learned to use rocks to break their tough shells.