Cephalopods play an important role in the Antarctic ecosystem, being consumed by a wide range of predators such as whales, fish, seals, albatrosses and penguins. To understand predator-prey interactions between top predators and cephalopods, effort has been put into the development of methods to determine the identity and size of world cephalopods using beaks since the 1950s (Clarke 1962a, b; Clarke 1966; Clarke 1977; Clarke 1980; Clarke 1986; Kubodera & Furuhashi 1987; Fiscus 1991; Smale et al. 1993; Xavier et al. 2007). The most used beak guide worldwide (Clarke 1986) is now out of print and is in need of urgent revision with additional material (Santos et al. 2001). Also, several new cephalopod species for the Southern Ocean have been recently described taxonomically, whose beaks need to be described and/or included in a guide (e.g. Collins & Henriques 2000; Lipinski 2001; Allcock & Piertney 2002).\ud \ud New efforts in the Southern Hemisphere allowed a new cephalopod beak guide to be produced (Lu & Ickeringill 2002), covering 75 species of cephalopods in Australian waters. Also new internet technology has been used to create a website to aid beak identification (http://research.kahaku.go.jp/zoology/Beak-E/index.htm) for Japanese waters. However, a cephalopod beak guide for the entire Southern Ocean is nonexistent and urgently needed.\ud \ud Here, we specifically aim to describe the main cephalopod beaks from species found in the diet of predators from the Southern Ocean (defined as south of the Subtropical Front) and adjacent waters in order to assist scientists and students interested in identifying cephalopods by the means of their beaks. Special attention was paid to providing photographs of typical beaks found in the diets of adults and juveniles when relevant. As a new tool applied to marine ecology, 3-D computer images of the most important lower beaks are also provided, where it is possible to rotate each beak 360 degrees and zoom in and out of particular key features of beaks in three dimensions. In addition, a review of the allometric regressions available is provided in order to relate cephalopod beak size to mantle length and mass as well as a review of the predators feeding on those cephalopod species
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