carinariidae

2

The extremely fragile and highly translucent shell commonly known as the Glassy Nautilus (Carinaria cristata) is produced by an impressively sized animal that is the largest heteropod of all, attaining a body length over 680mm. 

The shell is much smaller in comparison and rarely exceeds 70mm, it does not serve protective function and the animal cannot retract into the shell. A holoplanktic (i.e., planktic for its entire life) pelagic gastropod with a very wide range covering the entire Indo-Pacific, it is an active predator of a variety of zooplankton. As is the norm with zooplankton it migrates vertically through the water column diurnally and may thus be found from the sea surface down to a few hundred metres deep. 

The protoconch is tightly coiled but the teleoconch relaxes to a slightly curved pyramidal cap; it can be distinguished from other Carinaria species by the less curved shell and the extremely low keel.