Balearena gymnesica, enture shell 1 and protoconch.    From Wordnik.com.  [A fossil snail fits in between, or, maybe not] Reference

The fine spiral lines of the protoconch are more likely to represent the still developing mantle anatomy of the snail embryo at the time of the secretion of its embryonic shell.    From Wordnik.com.  [A fossil snail fits in between, or, maybe not] Reference

I'd be very interested in reading any studies that have examined the strength of genetic separation in examples like this same family, similar shell form, radically different protoconch.    From Wordnik.com.  [A fossil snail fits in between, or, maybe not] Reference

However, one significant trait distinguishes B. gymnesica from both Mastus and Napaeus: the protoconch, or the embryonic whorls, of Balearena have spiral lines on bottom halves of whorls, whereas the Mastus and Napaeus protoconches are always devoid of such microsculpture.    From Wordnik.com.  [A fossil snail fits in between, or, maybe not] Reference

There are very many such examples in the Australian Charopidae and the normal practice which I agree with is to regard such strong protoconch differences as automatically significant at generic level in view of the unlikelihood that there is much evolutionary pressure affecting protoconch fsculpture.    From Wordnik.com.  [A fossil snail fits in between, or, maybe not] Reference

Even before the snail hatches, it has formed a single small whorl around itself known as a protoconch.    From Wordnik.com.  [CreationWiki - Recent changes [en]] Reference

Growth: Even before the snail hatches, it has formed a single small whorl around itself known as a protoconch.    From Wordnik.com.  [CreationWiki - Recent changes [en]] Reference

As Altaba also notes, the protoconch microsculpture probably doesn’t have anything to do with burrowing, or for that matter, have any function at all.    From Wordnik.com.  [A fossil snail fits in between, or, maybe not] Reference