>Occasionally a
> researcher discovers a species which is so unique that it is
> obvious to him
> or her that it is new to science.  What is the minimum number
> of examples
> required to be considered?  I'm unable to find the answer in the ICZN.

Do you mean the minimum number of specimens? There is no requirement, but
the more the better. However, new species have been based on single
specimens.

> Second question.  How does one determine if a new species is
> juvenile, if he
> or she does not have a baseline to compare?

You can always have a baseline. I don't know much about chitons, but I can
give you examples from land snails. Almost all of the land snails I am
familiar with have at least 4 or 5 whorls when they are adults. So if I find
a shell that has, say, 3 whorls, I am almost certain that it is a juvenile.
If I find a bunch of adult shells in one location & a bunch of similar
looking, but smaller shells with less whorls at the same location, I am
certain that the smaller ones are the juveniles of the adult species. If you
really want to be sure, you take some live juveniles & raise them to
adulthood to see what they will look like. Many land snails form thick
and/or reflected lips with or without various folds & lamellae after they
become adults. So, a smaller shell with a simple thin lip is likely to be a
juvenile. Also, very young snails, especially the newly hatched ones,
usually look different in their overall proportions than the adults. I have
never compared their dimensions with those of adults, but the protoconches
appear to be more depressed with proportionately larger apertures. If you
look at enough of them, then you begin to recognize juveniles. So, again,
having lots of specimens of all sorts helps.

Aydin