Dive Dry with Dr. Bill

118: Paper Nautilus

One of the joys of diving the same location over many years is the discovery of "new" species or observing new behavior in a species already "well known" to me. Almost every dive brings something new and different, and this keeps me going after more than 1,000 dives in the Dive Park alone. One of those recent novelties was the shell of a paper nautilus. These shells appear in our waters occasionally, sometimes in large numbers. At least one other person observed a paper nautilus shell in the dive park the same day I did.

Many of you are familiar with its distant relative, the chambered nautilus. These animals are survivors from a group that emerged hundreds of millions of years ago (slightly before I started diving these waters). The shell is said to symbolize "perfection" and is often used in art and other decorative applications because of its series of internal chambers. These chambers are created as the animal, and its shell, grows. It is within the outer chamber that the soft bodied animal lives. However the chambered nautilus has a thick shell that affords much more protection than its "paper" thin relative's shell.

There are six species of paper nautilus, and they are found through warmer temperate and tropical oceans. However they are usually quite rare. Mass strandings of these animals have been noted in Mexico, Japan, Australia and elsewhere. I have heard of large strandings near Catalina's Isthmus as well. They are also known from the fossil record and, in fact, are the only surviving group of tetrabranch (four gilled) cephalopods.

The paper nautilus, sometimes called the argonaut, also has attracted attention since early sailors first observed them. Although both groups of nautiluses are cephalopods, related to octopi and squid, the paper nautilus is more closely related to the octopuses than to the chambered nautilus. However there is relatively little known about their biology and ecology. Like the octopus, they have eight arms but the sucker discs on them are very small. Only the female carries the shell, which in some species may be up to 12" long. She creates this shell using flared webs at the tips of two of her arms, rather than secreting it from the body as most other molluscs do. Although the chambered nautilus' shell has many chambers, the shell of the paper nautilus has but one. Its shell is used for floatation like a diver uses a buoyancy compensation device (BCD). The females use the shell as a brood chamber where they attach and incubate the eggs. She lives in the outer part of the chamber and carries the shell with her arms. Some reports state the male may also inhabit the female's shell.

The female is known to drop the shell when her batch of eggs hatches, or when she is disturbed. If a predator approaches, she may thrust the shell, with its ridge of small spikes, into the animal. Females make a new shell when they are ready to produce another batch of eggs. Females have been observed attached to jellyfish, and will drift along with them. The argonaut may get some protection from the jelly's tentacles.

The shell-less male is tiny (less than an inch) and has one very long arm which it coils close to its body. One early biologist thought this arm was a parasitic worm because he found it detached in the mantle cavity of a female, and described it as such in a scientific paper. Later he was surprised to discover that the "worm" was actually a structure known as the hectocotylus which is used to transfer sperm to the female. When mating, this arm breaks off (ouch) and crawls around inside the body of the female (like a French tickler according to one scientist). Its octopus relatives also possess this structure for mating, but they do not lose it in the process. The female is said to live much longer than the male, and may mate many times in her life while the male is believed to die afterwards. Double ouch!!

Of course the female lacks this structure. She possesses webbed arms which are used for feeding. When the male and female of the same species differ significantly in appearance, the species is called sexually dimorphic (exhibiting two forms). Some reports stated they eat plankton, jellyfish and salps in the upper water column during the day, others that they crawl along the bottom looking for food. If the first reports are true, they would be pelagic animals drifting in the open water. If the second is fact, they would be benthic animals living along the ocean floor. It is possible the reports of a benthic lifestyle result from confusion with the chambered nautilus which apparently feeds both on the bottom and in shallower waters.

Fortunately we have a "home grown" expert on the cephalopods that helped clear this up for me... Dr. Eric Hochberg of the Santa Barbara Museum of Natural History. In addition to adding his expertise to this article, Eric informed me that the first photographs ever taken of a paper nautilus were by another Avalon personality, Dr. Charles F. Holder. Holder, of course, was a co-founder of the Tuna Club (not to mention Pasadena's Rose Parade!). The photograph was probably taken in the old Banning aquarium housed where Antonio's Cabaret is now.

I was surprised to learn that in Japan, the paper nautilus is occasionally caught by the thousands and sold for food. I asked my friend and soon-to-be dive buddy Xiaoyan in Tokyo if she has ever tasted one. She recently e-mailed me to say she has never tried one, but Eric assures me they are very good eating. Perhaps Xiaoyan will bring some for dinner when she visits Catalina later this month. I have the nori... anyone for nautilus sushi? Pass the sake while you're at it!

© 2004 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays.

A chambered nautilus and views of a paper nautilus shell found just outside the dive park recently.

This document maintained by Dr. Bill Bushing.
Material © 2004 Star Thrower Educational Multimedia