Have you considered this may be a Pedipis species such as mirabelis?
(please forgive the spelling)
Leslie

Does it look like this one?
http://www.femorale.com.br/shellphotos/detail.asp?photo=25648.jpg
This came from Iceland.
I did some shelling in Costa Rica long time ago, but did not collect anythin
like this.
Marcus

From: David Kirsh
Reply-To: Conchologists of America List
To: [log in to unmask]
Subject: W/E mystery gastropod
Date: Sat, 26 Apr 2003 13:03:52 +0000

People,
I found the rocks at Punta Pelada on Costa Rica's Pacific coast were covered
with small live Littorina-like snails at the upper reaches of the intertidal
area, beyond most of the Nerites.
Keen has something from Puntarenas, C.R. she called Lacuna succinea Mörch,
but was uncertain about its true placement. The size of my specimen is about
right: 5 - 6 mm. But she says they are on seaweed rather than on rocks and
there's a chink-like umbilicus. Mine was clearly exposed on rocks and has an
obvious umbilicus. Surface is eroded and gray.
Anyone familiar with this ubiquitous gastropod? A Google search turns up
nothing. Maybe the name has been revised.
David Kirsh
Durham, NC