There are six living species of nautilus. They are called “living fossils” because they have existed for about 550 million years. Nautiluses live in shells that are divided into chambers. As they grow, they move into a new, larger chamber and close the old one.
Allonautilus perforatus is a species of nautilus native to the waters around Bali, Indonesia. It is known only from drifted shells and, as such, is the least studied of the six recognised nautilus species. A. perforatus shows a shell shape and coloration very similar to that of A. scrobiculatus and shares with this species the characteristic open umbilicus. However, it bears highly distinctive shell-ribbing, which is unique among extant ectocochliate cephalopods, and lacks scrobiculate shell sculpture. It is not known whether A. perforatus possesses the thick encrusting layer (periostracum) characteristic of A. scrobiculatus. Maximum known shell diameter is around 180 mm.
^Jereb, P. 2005. Family Nautilidae. In: P. Jereb & C.F.E. Roper, eds. Cephalopods of the world. An annotated and Illustrated catalogue of species known to date. Volume 1. Chambered nautiluses and sepioids (Nautilidae, Sepiidae, Sepiolidae, Sepiadariidae, Idiosepiidae and Spirulidae). FAO Species Catalogue for Fishery Purposes. No. 4, Vol. 1. Rome, FAO. pp. 51–55.
Barcode of Life Data Systems (BOLD) Stats Specimen Records:460 Specimens with Sequences:459 Specimens with Barcodes:421 Species:2 Species With Barcodes:2 Public Records:42 Public Species:2 Public BINs:2