Dear friends,

The genus Helix is a fairly tight group of large land snails.  In order to
give an answer to the question on their taxonomy, let me go over some
facts.

 It must be stressed that in the case of several species, their being
edible (and their ability to smuggle) has influenced their current ranges.
 For example, Helix aspersa was originally endemic to the southern tip of
Italy/Sicily, then it became circum-Mediterranean, and now is a pest
worldwide.  In addition, the obvious variation in shell shape, size and
coloration led to many 19th century conchologists to describe a bunch of
ethereal varieties/species.

Anatomical studies showed early on (by Moquin-Tandon, ca. 1850) that H.
aspersa differed markedly from H.pomatia.  The latter being the type
species of Helix, the name Cryptomphalus was proposed for aspersa.
 However, given the similarity in external appearance and shell shape, most
authors have treated Cryptomphalus as a subgenus of Helix. Resurrecting a
 long-forgotten name, some authors preferred to call this subgenus Cornu.

Likewise, H. aperta has almost unanimously assigned to its own subgenus,
Cantareus.  Helix (Cantareus) aperta is remarkably distinct even
externally, because the extended animal grossly exceeds its shell (i.e., it
seems to go along the line of semi-slugs), and when aestivating its
"operculum" kind of bumps out of the aperture.

In their 1995 monograph on the non-marine molluscs of Malta, Giusti,
Manganelli and Schembri made two relevant decisions.  First, they decided
to treat Cantareus and Cryptomphalus as genus-level synonyms, on the basis
of the shared presence of a peculiar sculture within the (invaginated)
penis.  Secondly, they decided to reject Cornu on the grounds that it was
based on a teratological specimen.  Even if not explicitly stated in its
original description, Cornu copiae Born, 1778 has a name evidently
referring to its "scalariform" shape.  I agree with Giusti et al in that
Born thought this unusual shape was a characteristic trait --ie., he was
not naming a three-legged chicken.  So they called the pest Cantareus
aspersus.

Some time later, on the Mollusca list somebody asked about the potential
impact of farming Helix aspersa in the United States (a bad idea anyway).
 I participated in that discussion quoting the proposed new name.  Roth
sent a message stating that before anyone started to mess with name
changes, Helix aspersa had to be known as such, thereby rendering the pest
clearly recognizable.  In their 2003 checklist of non-marine gastropods of
California, Roth and Sadeghian wrote (as quoted in a previous message) that
Cornu is valid because the teratological charater was not known initially,
and that it should be better used as a subgenus of Helix.  Likewise,
Falkner et al, in their 2002 checklist of non-marine molluscs of France,
argued that Cornu was valid for the same reason, but that it should be used
as a genus (i.e., Cornu aspersum).

So, we have three different questions:
1) Is Helix a genus encompassing pomatia as well as aperta and aspersa?
2) Should aperta and aspersa be included in the same genus-level cluster?
3) What is the valid name for the aspersa group?

From the foregoing discussion, and in my personal opinion, the answers are:

1) Yes, they all are best treated as Helix.  A genus should be considered
an adaptive cluster; i.e., a branch of the tree of life including all
species being closely related and sharing similar ecological traits.
 (Without this provision, we may soon end treating every single species as
representing its own genus, or even family!)

2) No, aperta is a very different animal from aspersa.  They share some
traits indicative of phylogenetic closeness, yet it is not reasonable to
include both of them in the same subgenus.

3)  H. aperta should be set in its own subgenus: Helix (Cantareus) aperta.
 As for aspersa, it is pity that the International Commission for
Zoologocial Nomenclature did not rule years ago in the sense of declaring
Cornu an unavailable name.  Without such ruling, and for the time being,
the pest should be called Helix (Cornu) aspersa.


Well, I hope you get the story...

Best wishes,

Cristian R. Altaba

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