Frequency of study and diversity of benthic hydrozoa of the argentine continental shelf

Abstract

The Argentine continental shelf was divided into 12 sectors every two degrees of latitude. All the bibliographical records and hydropolyp species found in each section were registered. The Hydrozoa of southern sections of the Magellanic zoogeographical province have been investigated since the nineteenth century, while in northern sections of this province and in the Bonaerensian zoogeographical province studies began in the early 1960s. The north section of the Magellanic zoogeographical province is the least known and shows less diversity. A total of 116 species were found. They are distributed among the families Sertulariidae (32.8%) Syntheciidae (1.7%), Campanulariidae (26.7%), Lafoeidae (10.3%) Plumulariidae (8.6%), Haleciidae (5.2%) Campanuliniidae (4.3%) Tubulariidae (2.6%), Bougainvilliidae (2.6%) Hydractiniidae (1.7%), Eudendriidae (1.7%), Corynidae (0.9%) and Clavidae (0.9%). Endemism was rare (8.5%) but 49.6% of the species have an austral distribution and 41.9% are cosmopolitan species. There are differences between the two zoogeographical provinces analyzed; the Magellanic zoogeographical province shows higher diversity (94 species), with 71 exclusive species, while the Bonaerensian zoogeographical province shows 48 species, 25 exclusive. Only 23 species were found in both provinces.