Crusty Nautilus, Allonautilus scrobiculatus

Allonautilus scrobiculatus, or the crusty nautilus, is a species of nautilus that is native to the waters around New Guinea, more specifically, New Britain and Milne Bay, and the Solomon Islands. A. scrobiculatus can be instantly recognized by its large open umbilicus, which is approximately 20 percent of the diameter of the shell at its widest point. This species, in addition to the closely related A. perforatus, were initially placed into the genus Nautilus, but have recently been provided their own genus because of the significant morphological differences. The most noticeable are features of the shell, including crease and encrusting layer that covers the majority of the shell. Reproductive structures and gills also differ drastically from the members of the genus Nautilus. The shell is normally around 18 centimeters in diameter, although the largest specimen that was ever documented measured 215 millimeters.

Image Caption: Allonautilus scrobiculatus. Credit: Mgiganteus1/Wikipedia (CC BY-SA 3.0)