Knowing Patagonia and its Mollusks

Patagonia is a geographic region in the southern end of South America. It is the southernmost continental area of the world (except Antarctica), reaching almost 56°S latitude. Patagonia is shared by Argentina (provinces of Neuquen (southern part), Rio Negro, Chubut, Santa Cruz and Tierra del Fuego ) and by Chile (regions: IXth, Xth, XIth and part of the XIIth). In Chile it is coincident with the South Longitudinal Valley in the southern part of the country. In Argentina, extends from Colorado River at 38°S up to the Great Island of Tierra del Fuego .

Among the most attractive sites to be visited in the Argentinean Patagonia we can mention:

•  Nahuel Huapi National Park , including San Carlos de Bariloche city and areas from Rio Negro and south Neuquen, with beautiful landscapes, snowed mountain tops, lakes of greenish or bluish iced waters, and hills covered by conifers and other gymnosperms.

•  Valdés Peninsula , placed in the North West of Chubut province and declared Humanity Patrimony, with marine elephants and wolves, and numerous bird species. Every year since July to November , its coasts become a reproduction area for the austral frank whales. It is one of the scarce continental places where this phenomenal takes place.

•  Perito Moreno National Park , in the North West of Santa Cruz province, where the magnificent wall of the glacial can be admired. From time to time, during the summer season the main structure of the Glacial brokes down, and huge blocks of ice fall down to the lake's waters providing a magnificent visual and sounding spectacle.

•  Bosques Petrificados Natural Monument , in the North East of Santa Cruz province. It is a paleobotanic deposit with big fossil trees which were part of large forests existing 130 million years ago.

•  Tierra del Fuego National Park , where the southern end of the Andes meets the Beagle Channel providing a great diversity of attractions. Much less known is Estados Island, separated from Tierra del Fuego Great Island by the Lemaire Strait. Many shipwrecks have taken place in its turbulent waters. In this island was placed a well known light house that oriented those brave marines that adventured themselves in those seas. Many of them shipwrecked in their goal to reach the Pacific Ocean countourning Cape Horn, inspiring Jules Verne to write his popular adventure novel “ Le Phare du bout du monde ”. It is well known that many victims of those shipwreckings survived feeding themselves with mollusks that populate the rocky beaches of that region. Among those mollusks, we can mention abundant mussels, and other species like Nacella deaurata and wonderful Trophon geversianus .

One of the famous naturalists that first came to Patagonia was Alcide d'Orbigny (1802-1857) who make an extensive trip through South America from 1825 to 1833. During his travel, he exhaustively explored Bolivia and the Brazilian Matto Grosso. He joint military expeditions to the Argentinean Indian frontier, watching Indian populations. The out coming scientific results from his trip include the study of almost seven-hundred species of marine, fresh water and terrestrial mollusks and the first description of more than three hundred nominal species exhaustively illustrated in his monumental work, “ Voyage dans l'Amerique Méridionale”.

Between July 1833 and June 1834, Patagonia was visited by Charles Darwin (1809-1882) aboard the Beagle as part of his world round trip which last since 1831 to 1836. The author of “On the origin of species by means of natural selection…” explored Rio Negro, Sierra de la Ventana, Santa Cruz and Tierra del Fuego. Darwin described with amazing precision its rich geological and biological observations together with other personal experiences while he was in contact with the Argentinean population. Like his predecessor, Darwin came into contact with aboriginal cultures while he navigated through the channels of Tierra del Fuego . Years later, between 1878 and 1879, the so called Second Conquer of the Dessert commanded by Julio A. Roca, led to the systematic elimination of aboriginal cultures, and to the incorporation of this huge region to the argentine national territory. Other important research efforts on Patagonian mollusks were the works by Watson, in 1876 ( H.M.S Challenger), King & Broderip (1831), Rochebrune & Mabille (1889), Smith (1877, 1885, 1902, 1915), Lamy (1906, 1911), Melvill & Standen (1907, 1912) Strebel (1904 to 1908), Powell (1951) and Dell (1964) ( Discovery Reports ), to mention some of them.

XVIII Century Patagonian map

The mollusk species that are present in the coasts of Patagonia permit to characterize two different zones or provinces.

The first one is the so called Argentine Malacological Province that runs from Bahia State in Brazil up to Golfo San Jose in Argentina. Water temperatures are warm to tempered, due to the influence of the Brazilian Current, which runs in the north to south direction up to the Rio de la Plata latitude. The most important Patagonian sites in this province are Golfo San Matías and Golfo San José. Among the remarkable shell species of this gulfs it can be mentioned big Adelomelon brasiliana , Odontocymbiola magellanica varieties (plate 1), some dwarf forms of Zidona dufresnei , Buccinanops globulosus , and Aequipecten tehuelchus scallop.

The second province is called Magellan Malacologic Province and extends from Golfo Nuevo in Argentina down to Tierra del Fuego and from there up to Conception in Chile on the West Coast. Patagonian coasts have in general low temperatures due to the influence of the Malvinas (Falklands) Cold Current, which runs in South-North sense. Some of the species found in this province are also present in Antarctic waters.

Among the most representative mollusks we have to mention genera Fissurella (plate 2), with several species abundant in the Chilean coast; Margarella (plate 3) and Photinula (Trochidae), Calyptraeidae, about fifteen Trophon (plate 4) and four of Xymenopsis , different Buccinidae, Buccinanops (Nassariidae), more than a tenth of volutes, and wonderful Turridae many of them still not described (plate 5). Among the bivalves we can mention several Pectinidae, and clams like Tawera, Eurhomalea (plate 6), Venus and other species (see plate 7, 8 & 9).

Inland of south Patagonia is mostly a plateau of low height with scarce and shrubby vegetation characteristic of dessert areas. The number of snail species that can survive is limited in this region by the low temperatures and poor vegetation. Discoleus ameguinoi (plate 10) is a Bulimidae which projects itself to the beaches areas from Rio Negro to Santa Cruz. In the northern region the landscape is exhibits some chains of old mountains and hills as the systems of Ventania and Tandilia. From those last geographical sites we can mention some isolated species of Plagiodontes and Cyclodontina (Odontostomidae), Austroborus (Strophocheilidae) (plate 11), and Discoleus (Bulimulidae).

Towards the west, near the southern end of the Andes Cordillera the ground level is higher.

In this region we found large andino-patagonian forests with higher rainfalls that attaint their maximum in the Valdivian Forest in Chile. In this area a fortnight of micro mollusks- today classified as belonging to the Punctoidea group - and several forms of Succineidae and Limacidae (hemi slugs) have been described. In the cordilleran areas of Rio Negro and Neuquen provinces we can find Plectostylus mariae (Bulimulidae), and Macrocyclis laxata (plate 12) which are probably among the most spectacular species in Patagonia. This mollusk, proper of the Valdivian Forest has a shell that reaches more than 110 mm in length, and belongs to a residual group that remembers Paryphanta from New Zealand.

Without any doubt Patagonia is one of the most privileged territories in the world because of its remarkable geography and unique characteristics. Many of the endemic mollusks present in the extensive Argentinean platform as well as in the inland territory are badly known to the international community and causes the fascination of scientists and collectors.

Plate 1. Odontocymbiola magellanica Gmelin 1791 Golfo Nuevo, Chubut Province, Argentina. At 12 to 18 meters depth.	Plate 2. Fissurella picta picta (Gmelin 1791) Near Porvenir, Magallanes Strait, XII Región, Chile	Plate 3. Margarella expansa (Sowerby 1838) Ushuaia, Tierra del Fuego Province, Argentina	Plate 4. Trophon geversianus (Pallas 1774) var. lamellosa Castellanos 1993 Estados Island, Tierra del Fuego Province, Argentina.

Plate 5. Leucosyrinx paratenoceras Powell 1951 150 km . SE of Mar del Plata, Argentina. At 100 meters depth.	Plate 6. Eurhomalea exalbida (Chemnitz1795). Lemaire Strait, Tierra del Fuego Province, Argentina.	Plate 7. Nacella deaurata (Gmelin 1790) Estados Island, Tierra del Fuego Province, Argentina.	Plate 8. Pareuthria plumbea ( Philippi 1845) Ushuaia, Tierra del Fuego Province, Argentina

Plate 9. Chlamys patagonicus King 1831 Ushuaia, Tierra del Fuego Province, Argentina	Plate 10. Discoleus ameguinoi (Ihering 1908) Punta Colorada, Río Negro Province, Argentina.	Plate 11. Austroborus dorbignyi (Doering 1876) Sierra de la Ventana, south Buenos Aires Province, Argentina.	Plate 12. Macrocyclis laxata (Férussac 1820) Huacho Cupil, South Chile.

Bibliography

• Darwin, Carlos. 1899. Viaje de un Naturalista alrededor del mundo . Tomo I. Biblioteca de jurisprudencia, filosofía e historia. Madrid. La España Moderna.

• Darwin, Carlos. 1899. Viaje de un Naturalista alrededor del mundo . Tomo II. Biblioteca de jurisprudencia, filosofía e historia. Madrid. La España Moderna.

• D'Orbigny, A. d', 1835-1847. Voyage dans l'Amerique Meridionale . Paris, C.P. Bertrand Ed., Vol. 5, Part 3, pp 1-758

• D'Orbigny, A. d', 1835-1847. Voyage dans l'Amerique Meridionale . Paris, C.P. Bertrand Ed., vol. 9.

• Fernández, Delicia. 1973. Catálogo de la Malacofauna Terrestre Argentina. Comisión de Investigaciones Científicas, La Plata, provincia de Buenos Aires

• Forcelli, Daniel Oscar. 2000. Moluscos Magallánicos. Guia de moluscos de Patagonia y sur de Chile. Vazquez Massini Editores. 200 pp.

• Marco, J. y Samopablo R. (dir.). 1992. Gran Diccionario Salvat. Salvat Editores, S.A. Barcelona. Edición Especial para La Nación. En tres tomos.

• Olascoaga, Manuel J. 1881. La Conquête de la Pampa. Recueil des documents relatifs a la Campagne du Rio Negro. Comprend l'itinéraire suivi par toutes les colonnes expéditionnaires qui, sou les orders du ministre de la guerre, Général D. Julio A. Roca ont occupé le désert la ligne de frontiére sur le Rio Negro. Buenos Aires. Imprimerie du “Courrier de la Plata”.