>Have any of you Trivia fanatics have observed small spurs
>(threads)running our of the concentric cords.
 
Some triviids have weak "axial" sculpture that is visible in between the
ribs. I'm not sure if this is what you mean by "spurs" or "threads". The
sculpture that I've seen gives a slightly scalloped effect to the spaces
between the ribs, particularly on the right side of the shell, if viewed
obliquely with a strong light source.
 
Near the outer lip of the shell, this sculpture is at right angles to the
ribs, but as you follow it back across the dorsum to the left side of the
shell, the angle changes. This sculpture marks the position of the lip in
the juvenile shell. As the shell approaches maturity I think it makes small
axial ribs that strengthen the thin bulla stage. These ribs are largely
obscured when the transverse ribs of the mature shell are laid down on top
of them. I haven't checked many species to see how widespread this pattern
is, but it is present in Robertotrivia eos, one of the largest triviids, as
well as the Hawaiian species, most of which are quite small.
 
Gary
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Gary Rosenberg, Ph.D.                     [log in to unmask]
Malacology & Invertebrate Paleontology    gopher://erato.acnatsci.org
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