Hi -
Don't know if this will help or not:
In my research on ammonites and other fossil (and modern) shelled cephalopods I came across this article that introduces Allonautilus as a genus:
Ward, Peter and Saunders, W. B., 1997, Allonautilus: a new genus of living nautiloid cephalopod and its bearing on phylogeny of the Nautilida, in Journal of Paleontology, vol. 71, p. 1054-1064. You might find it interesting if you haven't seen it. Looks like Allonautilus is actually a valid genus (I deal mainly with shell morphology and morphometrics, and if I had just fossils to rely on I'd definitely separate them, and I'm definitely not a "splitter" by any means when it comes to taxonomy). Not only does the shell have much flatter sides than Nautilus (implying in part a depth restriction), but the animal itself is apparently quite different from the animals in members (one or several depending on who's talking) of the genus Nautilus.
In the article they also introduce the name Allonautilus perforatus for specimens from the area around Bali - these are the ones with the faint raised ribs. Although there are definitely some consistent differences between this form and the more typical scrobiculatus from the Solomon Islands area, I'm hesitant after examining specimens of both to consider them separate species but perhaps subspecies or (if someone doesn't like that term) at least forms or geographical variations. The typical scrobiculatus from the Solomons have domnantly fine but readily seen spiral surface ornamentation, while on the perforata form this is not evident, and instead there are several raised but broad low ribs extending from the umbilical shoulder area toward the venter. The color pattern tends to be different, also. Also, in perforata, all the specimens I examined are indeed perforate (if you look into the umbilicus there is a tiny hole you can see light through) - unlike the typical scrobiculatus. (of course, some specimens of Nautilus pompilous from the Philippines show this, and have even been marketed as N. stenomphalus even though that species (stenomphalus) is from Australia and doesn't look anything like pompilous!).
Interestingly, specimens of the perforatus variation have been more readily available from dealers in recent years - I noticed two dealers selling them (all fspecimens from Bali) as well as the more typical scrobiculatus (from the Solomons) in the last year and a half.
- Rick Batt
________________________________
From: Conchologists List on behalf of Andrew Grebneff
Sent: Thu 4/3/2008 6:38 AM
To: [log in to unmask]
Subject: Re: [CONCH-L] Shelling in Bali/Java: ribbed Nautilus
>Andrew, Nautilus scrobiculatus Lightfoot, 1786 to the best of my
>knowledge, are usually from Ambon Island. Out of 1000 Nautilus
>pompillus Linneus, 1758 found, there should be about 6 - 8
>scrobiculatus's..I heard they are found on Lombok Island, also, but
>mine were all from Ambon Island , North Maluku's.
Thanks. It is not too rare in the Solomons. I expect that its
distribution will eventually be found to be wider than the
currently-known limits.
I am far from sure that the ribbed Borneo specimens are a local morph
or a good species. Nobody has followed it up! Need some
live-collected specimens with animal preserved... heck, and some good
images of living specimens underwater!
--
Regards
Andrew
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