Pteropoda
Distribution in the South Atlantic

According to their affinities with water masses (Surface water masses, Vertical water-mass structure), pteropods of the South Atlantic can be divided into warm water, cold water, Subantarctic and Antarctic species. No transitional forms are known in the area.

The warm water fauna is the most diverse, with more than 80 taxa of Thecosomata and Gymnosomata. It inhabits equatorial and subequatorial waters, reaching a southern distributional limit at the Subtropical Front. The Pseudothecosomata are restricted to this region.

Though poor in diversity, Euthecosomata and Gymnosomata are abundant in cold waters. The commonest cold water species is Limacina helicina antarctica, its geographic range extending from the Subtropical Front to the Antarctic coast. Limacina helicinaantarctica f. antarctica is the dominant pelagic gastropod in Antarctic waters. Swarms of this species with densities over 10,000 ind. per 1000 mö3 were found south the Antarctic Convergence near 65°S (Chen, 1968a). Limacina helicina antarctica f. rangi is very frequent in Subantarctic waters. In the Argentine Sea and surrounding areas, large numbers of that species inhabit the slope and penetrate the shelf water up to the 100 m isobath, more exceptionally up to the 50 m isobath (Dadon, 1989). Here the swarms seem to be smaller (Dadon, op. cit.).

Other cold water species are the Thecosomata Limacina retroversa australis and the Gymnosomata Clione limacinaantarctica and Spongiobranchaea australis. Limacina retroversa australis is clearly a subantarctic species, whereas both Gymnosomata are present from the Subtropical Front to the Antarctic coast.

Table Pteropoda lists the world wide biogeographic affinities by species; further details are given below.

• Limacina bulimoides (Limacina bulimoides map). The dominant pteropod in the Benguela Current (Morton, 1954), where its abundance may exceed 350 ind. per mö3 (Dadon and Masello, in press).li>
• Limacina helicina antarctica forma antarctica (L. helicina antarc. f. ant. map). Cold water stenothermic. Present in the Southern Ocean from Antarctic coastal waters to the southern part of the West Wind Drift. li>
• Limacina helicina antarctica forma rangi (L. helicina ant. f . rangi map). Present to the northern limit of the West Wind Drift, but extending with the Malvinas (=Falkland) Current as far north as the Brazil-Malvinas (=Falkland) Convergence. Near South Africa it occurs to 30°S. North of the Weddell Sea the southern boundary of this form bends southwards. A cline seems to develop, with the forma rangi at the northern extreme and the forma antarctica at the southern end (Dadon, 1993).li>
• Limacina inflata (Limacina inflata map). Very abundant in the Brazil Current (reaching 38 ind. per mö3), but its numbers decrease in the Central Atlantic and in the Benguela Current (Dadon and Masello, in press).li>
• Limacina lesueuri (Limacina lesueuri map). Most abundant in the Central Atlantic, with densities to 24 ind. mö-3 (Dadon and Masello, in press), and frequent but not abundant in the boundary currents.li>
• Limacina retroversa australis (L. retroversa australis map). The most abundant pelagic mollusc in Subantarctic waters, with up to 67 ind. per mö3 (Dadon, 1990a, b), exceptionally to 1,000 ind. per mö3 (Boltovskoy, 1971a, b). Its geographic range in surface waters extends from the Subtropical Front to 3-10 degrees south of the Antarctic Convergence (Chen, 1968a; Dadon, 1993). Off southern South America it is very abundant in the slope and shelf water up to the 100 m isobath (south of 41°S; Dadon, 1990a). The shelf becomes narrower to the north, and here swarms drift to the coast and the species is recorded up to the 50 m isobath (Dadon, 1989). L. retroversa occurs near Cabo Frio (Massy, 1920), but this may be the result of frequent local upwellings (see "General biological features of the South Atlantic"). Swarming in neritic waters is associated with retention areas on the outer shelf, but even these areas cannot prevent a massive seasonal migration of stocks into the oceanic zone (Dadon, 1990a).li>
• Limacina trochiformis (Limacina trochiformis map). Abundant in the Brazil Current (up to 1.8 ind. per mö3 off Cabo Frio; Dadon and Esnal, 1995), but absent east of 10°W (van der Spoel, 1967).li>
• Cavolinia inflexa formae inflexa, imitans and labiata. C. inflexa is a warm water species. C. i. forma labiata shows a tendency for bisubtropical distribution, more abundant in the South Atlantic, South Indian, and Pacific Oceans, but also present in the Mediterranean. In the Indian Ocean a population of C. i. forma labiata is found between 0° and 40°S, and a smaller population occurs in the central and southern Arabian Sea. The South Indian and Atlantic populations are connected by the population in the Agulhas Current, composed of a mixture of the forms inflexa (C. inflexa f. inflexa map) and labiata (C. inflexa f. labiata map). In the Pacific the species does not occur north of 40°N, in contrast to the Atlantic population which reaches 55°N. C. i. forma inflexa is the most common form in the North Atlantic. C. i. forma imitans is found in the Atlantic and near Zanzibar. In the Atlantic it occurs between 55°N and 45°S, and is absent in the Benguela Current and off northern South America. li>
• Clio andreae (Clio andreae map). Only 3 small populations are recorded south of 5°N: off Cabo Blanco, off Cape of Good Hope, and in the Argentine Basin. li>
• Clio cuspidata (Clio cuspidata map). Found east of 40°W between 65°N and 20°S. In the southern part of the Eastern Atlantic, influences of Benguela Current are evident. li>
• Clio piatkowskii (Clio piatkowskii map). Recorded in the Weddell Sea at great depth.li>
• Clio pyramidata forma antarctica (Clio pyramidata f. antarct. map). This form occurs immediately south of the area of Clio pyramidata forma lanceolata (Clio pyramid. f. lanceolata map). It is found in the Western Atlantic between 20°S and 55°S, south of the Agulhas Current south of Australia and New Zealand at 50°S, and west of Chile at 50°S. It normally inhabits Antarctic Intermediate Waters and Subantarctic Intermediate Waters (Chen, 1966). It is frequent, but not abundant, and widely distributed between 40° and 60°S. It is rare at the surface, with maximum densities reaching about 200 ind. 1000 mö-3 (Chen, 1968a). Never found in neritic areas off South America (Dadon, 1989).li>
• Clio pyramidata forma sulcata (Clio pyramidata f. sulcata map). Recorded between the area of Clio pyramidata forma antarctica and the Antarctic Continent. South of Australia, between 180°W-160°W and 140°W-90°W, the forma sulcata seems absent. It is characteristic for Antarctic water, and found from the Antarctic Convergence to the Antarctic coast. It is not abundant; dense patches were observed only in the South Sandwich Trench, reaching 10,000 ind. 1000 mö-3 (Massy, 1932; Chen, 1968a; Ramírez and Viñas, 1983).li>
• Creseis acicula forma acicula (Creseis acicula f. acicula map). Coastal areas off Brazil. li>
• Creseis virgula forma virgula (Creseis virgula f. virgula map). Frequent in Brazilian neritic waters, and some vague records in the Caribbean Area, in addition to those of a small population in the Gulf of Darien.li>
• Diacavolinia limbata forma limbata (D. limbata f. limbata map). Present in the upwelling area off Northwest Africa and the tropical western Atlantic. li>
• Diacavolinia strangulata (Diacavolinia strangulata map). Originally described from the West Pacific Ocean, but probably has a wider distribution.li>
• Styliola subula (Styliola subula map). Frequent in the Brazil Current (to 60 ind. 1000 mö-3; Dadon and Esnal, 1995). One exceptional record at 64°S is due to expatriation by local currents.li>
• Cymbulia peroni morpha peroni (Cymbulia peroni m. peroni map). Present in the Mediterranean and occasionally in the Atlantic. li>
• Peraclis bispinosa (Peraclis bispinosa map). Recorded from 60°N (northwest of Iceland) to 25°S (off the West African coast).li>
• Peraclis depressa (Peraclis depressa map). Typical for the eastern Atlantic, occurring in the eastern and southern basins.li>
• Peraclis valdiviae (Peraclis valdiviae map). In the Pacific, isolated records from the Gulf of Panama, the Tasman Sea and the Indo-Malayan archipelago. Numerous records from the northern and southern Indian Ocean and the entire Atlantic Ocean. It clearly occupies shallower depths in colder areas than in warmer areas, with pronounced subtropical submergence at 40-45°N and 40-45°S. li>
• Cephalobrachia macrochaeta. Bathypelagic (below 1000 m) between 65°N-10°S, in colder areas also between 400 and 750 m. Probably a cosmopolitan deep-sea species. li>
• Clione limacinaantarctica (Clione limacina antarctica map). This is the dominant Gymnosomata in Antarctic waters (Chen and Ericson, 1967), extending to the Subtropical Front. In neritic water it is present on the outer shelf up to the 100 m isobath (Dadon and Chauvin, 1998).li>
• Spongiobranchaea australis (Spongiobranchaea australis map). The most frequent Gymnosomata in subantarctic waters, also present in the Antarctic; it is found in close association with its prey, Limacina helicinaantarctica and L. retroversa australis. In neritic waters it occurs on the outer shelf, eventually reaching the 80 m isobath (Dadon and Chauvin, 1998).li>
• Spongiobranchaea intermedia (S. intermedia map). Probably a eurythermic, cosmopolitan species. Known from only four localities; Panama, Dakar, Argentine waters and the Tasman Sea. li>
• Thliptodon antarcticus. Its Antarctic record is dubious as it was reported by Meisenheimer from a single sample from the Valdivia expedition in which many tropical organisms were present at an extremely southern locality (incorrect labeling?).li>

Table Pteropoda, World wide biogeographic affinities of pteropod species.