Amygdalum papyrium (Conrad, 1846), Atlantic Paper Mussel

[Marlo]

Amygdalum papyrium (Conrad, 1846)

This is a beautify shell that can only be appreciated when seen just collected live from the water. It is among that group of bivalve shells that is capable of displaying an iridescent rainbow of colors. However, the natural brilliance of its coloration fades quickly. I attempted to capture the iridescence in these photos, and was able to come close to capturing the rich coloration. In her book Bivalve Seashells of Florida: An Identification , Trish Hartmann comments that A. papyrium has "faint, tan, zigzag lines which are just barely visible." While some varieties of this species are rather dull in coloration, the below photos illustrate that A. papyrium can be a striking shell.

I have found A. papyrium in lagoonal waters on both sides of Florida, but have not found it in the Florida Keys. It is always found among grasses on bottoms that have a muddy component. The bottom in the Florida Keys is mostly composed of coral silt and sand, which may be why I've yet to find A. papyrium there.

This specimen was taken at Jupiter Sound, Palm Beach County. Florida. 18 mm Photos by Marlo Krisberg

[HGLee]

Thanks for presenting this feature, Marlo. I have reviwed all the relevant material in my collection, done literature and on-line research, and formulated a re-analysis of this species in NE Floruda. I can now trace the growth of this mussel from under 2 mm to over 35 mm. It undergoes a fairly consistent evolution of characters from conspicuously marked with red-brown, purplish, or even dark green zigzag markings to a bicolored apple green with obsolescent to obsolete zigzagging in more mature shells. Meanwhile the shape becomes more slender and ventrally deflected. Although there is a surprising plethora of images off the striking juveniles on the Internet, standard and respected published works, e.g., Abbott (1974), Mikkelsen and Bieler (2008), mention neither the allometry nor evanescent (ontogenetically, that is) color pattern. I am ashamed to say I misidentified not my own material (Lee, 2009: 116) from Big Talbot Island (see below) as Amygdalum sagittatum. I now see I have shells of what Timothy Abbott Conrad named Modiola papyria from Duval, Brevard, Palm Beach, Levy, Taylor (2 stations), and Bay Cos., FL as well as Bahia, Brazil (HGL! 8/65).

I have also been influenced by Huber (2010), who drives a wide phylogenetic wedge between the two genera Arcuatula and Amygdalum.

Drawing from the above resources, I have come up with this schema for the three patterned Recent Paper Mussels in Florida waters:

Arcuatula Jousseaume in Lamy (1919: 173). Type species by tautonomy: Modiola arcuatula Hanley, 1844: 16, Recent: Southeast Asia.
Modiola papyria Conrad, 1846 Maryland to Brazil
Amygdalum sagittatum Lee, 2009: 16 non (Rehder, 1835) in partim [one cited lot juveniles taken from Big Talbot Island drift]

Amygdalum Mühlfeld, 1811 Type species by monotypy: Amygdalum dendriticum Mühlfeld, 1811, Recent: Gulf of Mexico to Brazil.
Amygdalum dendriticum Mühlfeld, 1811
Mytilus arborescens Chemnitz 1895: 251; pl. 198, figs. 2016, 2017) [Unavailable for purposes of taxonomic nomenclature; work not consistently binominal].
Mytilus arborescens 'Chemnitz' Fischer von Waldheim, 1807 [This nominal taxon, apparently the earliest available name for the biotaxon, may meet criteria for nomen oblitum.]
Mytilus arborescens 'Chemnitz' Dillwyn (1817: 306)
Modiola picta Lamarck, 1819: 112-113 [Type figure (Bruguière, 1797: pl. 221, fig. 2)]
Amygdalum sagittatum Lee, 2009: 16 non (Rehder, 1835) in partim[Xalvis Island: hypotype]
Modiolus sagittatus Rehder, 1935 [Figure of holotype: <http://www.biodiversitylibrary.org/item/34874#page/155/mode/1up>]

N.B. Distinction between Amygdalum dentriticum and A. sagittatum has been blurred by the consistent reference to "cobwebbing" in the pattern of the latter. In fact the color pattern of former species is more aptly thus characterized.

Short version: I agree with your diagnosis at the species level but feel the taxon should be reassigned to Arcuatula Jousseaume., i.e., Arcuatula papyria (Conrad, 1846) Atlantic Papermussel.

Abbott, R.T., 1974. American Seashells (Second Edition). Van Nostrand Rheinhold Co., New York. Pp. 1-663 + 24 pls.

Bruguière, J.G. [ed.], 1797. Tableau encyclopédique et méthodique des trois règnes de la nature vers, coquilles, mollusques et polypiers tome second. Agasse, Paris. Planches 190-286. 8 July.

Chemnitz, J.H., 1795. Neues systematisches Conchylien-Cabinet 11: pls. 174-213 [not seen; see Richardson et al.]

Conrad, T.A., 1846. Descriptions of new species of fossil and Recent shells and corals. Proceedings of the Academy of Natural Sciences Philadelphia 3: 19-27.
<http://www.biodiversitylibrary.org/item/17669#page/32/mode/1up>

Dillwyn, L.W., 1817. A descriptive catalogur of Recent shells (2. vols.). Londin. xii + 1-1092. <http://biodiversitylibrary.org/item/43021#page/324/mode/1up>

Hanley, S., 1844. Descriptions of new species of Mytilacea &tc. Proceedings of the Zoological Society of London 12: 14-18.
<http://www.biodiversitylibrary.org/item/46217#page/28/mode/1up>

Huber, M., 2010. Compendium of Bivalves. ConchBooks, Hackenheim, Germany. Pp [1]-901. August.

Fischer von Waldheim, G., 1807. Muséum Demidoff, ou catalogue systématique et raisonné des curiosités de la nature et de l'art. vol . 3 Végétaux et animaux. Moscau (Moscow), Russia. Pp 1-330. [not in my library nor available on-line]

Lamarck, J. B. P. A. de M. de, 1819. Histoire naturelle des animaux sans vertèbres présentant les caractères généraux et particuliers de ces animaux, leur distribution, leurs classes, leur familles, leurs genres, et la citation des principales espèces qui s'y rapportent; précédée d'une introduction offrant la détermination des caractères essentiels de l'animal, sa distinction du végétal et des autres corps naturels; enfin l'exposition des principes fondamentaux de la zoologie. [Première édition] Tome 6 Partie 2. Lamarck, Paris. i-vi + 1-343. Feb. to June.
<http://www.biodiversitylibrary.org/item/26549#page/124/mode/1up>

Lamy, E., 1919. Les Moules at les Modioles de la Mer Rouge. Bulletin du Museìum national d'histoire naturelle 25: 173-178. <http://www.biodiversitylibrary.org/item/27186#page/195/mode/1up>

Lee, H.G., 2009. Marine shells of northeast Florida. Jacksonville Shell Club, Jacksonville, FL. Pp. (1)-204 incl. numerous text figs. + 19 color pls. 28 May.

Mikkelsen, P.M. and R. Bieler, 2008. South Florida seashells living marine mollusks of the Florida Keys and adjacent regions. Bivalves. Princeton University Press, Princeton, NJ. -viii + 1-503.

Mühlfeld, J.K.M. von, 1811. Entwurf eines neuen system's der schaltiergehüse. [I]Magazin. Gesellschaft Naturforschender Freunde zu Berlin 5: 38-72. 31 Dec.
[not in my library or available on-line]

Rehder, H.A., 1935. New Caribbean marine shells. The Nautilus 48: 127-130. April. <http://www.biodiversitylibrary.org/item/34874#page/151/mode/1up>.

Richardson, L., R.T. Abbott, and G.M. Davis, 1979. Early references to the figures in the Conchylien Cabi [sic] of Martini and Chemnitz: volumes I-XII. Tryonia 2(1,2): 1-225 + iv + 193 pls + 44 vignettes; 226-427 + 237 pls. [195 A, B] + 26 vignettes. August 1.


Turgeon, D.D., J.F. Quinn, Jr., A.E. Bogan, E.V. Coan, F.G. Hochberg, W.G. Lyons, P.M. Mikkelsen, R.J. Neves, C.F.E. Roper, G. Rose nberg, B. Roth, A. Scheltema, F.G. Thompson, M. Vecchione, and J.D. Williams, 1998. Common and scientific names of aquatic invertebrates from the United States and Canada: mollusks, 2nd edition. American Fisheries Society, Special Publication 26. Bethesda, Maryland. ix + pp. 1-509 + 16 pls. (unpaginated).

Harry G. Lee