| The Atlantic Partridge Tun |
| By Harry G. Lee, M.D. |
 One of the more unusual marine mollusk records for
northeast Florida waters is the occurrence of the Atlantic Partridge Tun. It is
one of a very few locally-collected species on which I personally have never
laid a hand, but documentation was secured by Charlotte Lloyd, who came across a
living specimen at a depth of 128 feet 45 miles east of Mayport on August 6,
1991. Being conservation-minded, yet wanting to placate skeptics of "(shell)fish stories," she chronicled the encounter on videotape just before releasing the
snail!Aside from Charlotte's unusual coup, there is a bit more to say about this critter - partly its natural history, but more so the history of its naming. The unraveling of this paper trail took me through two and a half centuries of literature and provided a few general lessons in the sometimes complex process of taxonomic nomenclature. The Atlantic Partridge Tun  (see
figure 1., a 40 mm. juvenile from Eleuthera, Bahamas
in the Lee Collection), is widely known as Tonna maculosa (Dillwyn,
1817), a name proposed as "Buccinum perdix .... Variety ... Buccinum
maculosum." on page 583 of volume 2 of this work (see bibliography for this
and other citations). Lewis Weston Dillwyn recorded two references. The first
was "Solander [actually Lightfoot, 1786  ] lot 3050 p. 136" [sic; error
for 137]. In Lightfoot (1786) this entry reads "A very fine variety of Buccinum
maculosum, S. or spotted Tun, undescribed from New Holland -
very rare" [Lightfoot's italics]. The "S." connotes a name in a
Daniel Solander manuscript - possibly only on the label appended to the specimen
in question. Unfortunately the passage I quoted was all Lightfoot wrote; there
is no cited illustration and insufficient text for this to stand as a
validly-proposed taxon; ergo Buccinum maculosum Solander [Lightfoot,
1786] is a nomen nudum and unavailable for taxonomic nomenclature
(International Code for Zoological Nomenclature (ICZN) Article 12; Criteria of
Availability; see ref. below). How Dillwyn knew what Lightfoot had before him
is uncertain, but he may have seen the actual shell, which was to have been sold
at auction on Thursday May 25, 1786 according to the "Portland Catalog" (when
Dillwyn was in his ninth year of life) at some point. Needless to say, the
species is more than "very rare" in New Holland (Australia) as it does
not live there. Dillwyn's other (second) citation was Seba vol. 3, pl. 68,
fig. 16 (see figure 2, taken from Müsch, I., R.
Willman, and J. Rust [eds]). Although the text of the non-binominal Seba work
is not available for taxonomic nomenclature, this illustration almost certainly
depicts the western Atlantic taxon in question - the editors' misidentification
of it as Tonna perdix (Linnaeus, 1758) notwithstanding. Dillwyn was
correct in recognizing his Buccinum maculosum as a new taxon!
Unfortunately, however, a quarter century earlier Gmelin (1791, p. 3476, no. 22)
applied that same binomen to a different shell, which we now know as the west
African Cassis tessellata (Gmelin, 1791)  [Buccinum tessellatum
op. cit. p. 3476, no. 20]; see Abbott (1968; p. 54). The Dillwyn name is a
primary junior homonym of Buccinum maculosum Gmelin, 1791 and therefore,
until recently (see last paragraph),
unavailable for taxonomic nomenclature according to the ICZN Article 52;
Principle of Homonymy (ICZN, 1985).Wait.... it gets more complicated! In looking further into the synonymy in Tucker's Cassis monograph (Abbott, 1968; p. 54), I saw that the binomen Buccinum maculosum was validly proposed by an even earlier authority, Thomas Martyn (1784)! Because Martyn's Universal Conchologist was not a consistently binominal work (like Seba), the International Commission for Zoological Nomenclature exercised its plenary powers (Anon., 1957) to declare most of Martyn's names invalid, while conserving the names applied therein to nine well-known New Zealand marine gastropod species. View The Nine Species Among these is Buccinum maculosum Martyn; now Cominella maculosa (Martyn, 1784). The consequence of this discovery is that B. maculosum Gmelin, like B. maculosum Dillwyn, would not be not available (primary junior homonymy, again; using ICZN, 1985). Since authors hadn't used B. maculosum Gmelin, quite possibly because it was reported as a junior synonym of B. tessellatum Gmelin by Dillwyn (1817; p. 596, no. 20), who appears to be the First Reviser (ICZN Article 24). It is possible that Dillwyn chose B. t. over B. m. because it appeared earlier in the Gmelin work (on the same page, two species above it, a convention referred to as "position priority," employed by some taxonomists in the past but never codified by ICZN) or perhaps because he thought the earlier Solander [Lightfoot] (nude) name rendered Gmelin's Buccinum maculosum unavailable. Whatever the machination, the outcome is that the cassid (helmet shell), unlike our tonnid (tun shell), nomenclature avoided being threatened with mass confusion by the loss of a such well-travelled binomen as Tonna maculosa (Dillwyn), the topic of this discussion.
Armed with all this
information about synonyms, homonyms, availability of nomina, etc., I was
getting ready to dismantle the underpinnings of the Atlantic Partridge Tun
nomenclature until a very perceptive correspondent of mine, Marien Faber
tactfully pointed out the value of "reading the directions" before launching
such an ambitious campaign. Marien indicated that the ICZN (1999;
fourth edition) contained an important policy change versus between the
third (1985) edition. Until 2000 a primary junior homonym (e.g. Buccinum
maculosum Gmelin, 1791; B. maculosum Dillwyn, 1817) was deemed
unavailable for taxonomic nomenclature (see end of
paragraph four) by the ICZN, and could only be conserved by petition to the
Commission to exercise its "plenary powers." The current (fourth; 1999) edition
states (Article 23.9.5): "When an author discovers that a species-group name in
use is a primary junior homonym of another species-group name also in use, but
the names apply to taxa not considered congeneric after 1899, the author must
not [our emphasis] automatically replace the junior homonym; the
case should be referred to the Commission for a ruling under the plenary power
and meanwhile prevailing usage of both names is to be maintained." Short
version: the burden of petition is shifted from authors who wish to conserve (a
majority of) primary junior homonyms to those authors who wish to suppress such
names. Ergo, until told otherwise, we are legit in using Tonna maculosa
(Dillwyn, 1817) as did the overwhelming majority of the authors who taught us
much of what we know of the Atlantic Partridge Tun.
|
Wait; there's still more. Helix sulphurea C. B. Adams, 1849 (p. 33) was
first reported from Jamaica, and the author gave a short description, noted the
size (0.175 inch across by 0.16 inch high), and stated; "Perhaps this is a young
shell, but probably not of any described species." The next year he returned to
this taxon and wrote (C. B. Adams, 1850; page 98): "On page 33 we described
Helix sulphurea as 'perhaps a young shell.' This opinion was founded on its
papyraceous appearance. Mr. Chitty, from whom the original specimens were
received, has recently furnished a series, which shows that this shell, with all
the generic characters of Helix, is the last embryonic stage of the West
Indian variety of Dolium perdix!" [his exclamation point]. I believe
figure 3. is very much like what C. B. Adams had
before him in 1849 (and Chitty somewhat later). This is a photomicrograph of
the apex of the same shell as in figure 1. It shows an intact
ultraplanktotrophic protoconch reflecting a very long swimming veliger stage, an
attribute which no doubt accounts for the wide dispersal of this species and
many of its confamilial relatives. 
It appears the next available name for the Atlantic
Partridge Tun is Dolium pennatum coined by the Danish conchologist Otto
Andreas Lowson Mørch (he actually signed this work "Mörch;" see below) from the
"Antill." It was published in another public auction catalog - that of the
Alphonso .... de Yoldi collection (its 4,012 lots rivaling the 4,156 of the
Dutchess of Portland). Mørch's indication (lot 2058; p. 110) was an
illustration in Martini - vol. 3, fig. 1078 (see figure 4).
This is interesting because Martini himself called it a juvenile of Buccinum
[now Tonna] perdix Linnaeus, 1758 and showed it alongside two
adult T. perdix! Nonetheless this juvenile shell shows the color pattern
of the W. Atlantic species (look at the smudgy pattern on the penultimate whorl
in figure 1) - not the Indo-Pacific T. perdix, with which it seems to
have been confused/associated by many authors. Ergo Tonna pennata (Mørch,
1852) refers to the Atlantic Partridge Tun, and the Partridge
Tun, T. perdix (Linnaeus, 1758) from the Indo-Pacific is closely related
- and not just biologically and by its vernacular name: Pennata probably
means "feathered" in reference to its color pattern, which a century before
likely inspired Linnaeus' perdix, Latin for "partridge."
