>How can one tell a true dwarf Nautilis pompilius from
>one that is just juvenile?   Is the umbilicus open in
>the little ones, and if so up until about what size or
>how many whorls?

A juvenile Nautilus pompilius has open umbilicuses, though they are
very narrow chinks. You can see through the umbilical perforation. If
small enough you can see the characteristic nautiloid (as in
superfamily Nautiloidea) nepionic constriction, a radial (axial)
groove acroos a whorl secreted at the time of hatching from the
egg... they are big eggs and the animal is large when it hatches.

I have a specimen 0f 65mm diameter, and the nepionic constriction is
visible in the black area at whorl-height 15mm. The umbilicuses are
just barely open; on the right I can just see a black opening; on the
left I could possibly insert a pin.

I don't believe there is such a thing as a dwarf Nautilus, though
some specimens are geronitic at well under 20cm diameter. But if
there were, you'd need a geronitic one to be able to tell, which
would display the broadened body-chamber and blackened lip of the
well-aged.

>From the land of the best Pipers on the Planet,
>Ross M.

Do those pipers peep?
--
Regards
Andrew