The nematodes were collected from the penguin Spheniscus magellanicus (Forster) (Sphenisciformes). A study from the main species of Contracaecum that occur in penguins and piscivorous birds from the south hemisphere is made, more specifically the C. eudyptulae Johnston & Mawson, 1942a, C. eudyptes Johnston & Mawson, 1953, C. heardi Mawson, 1953, C. antarcticum Johnston, 1938, C. prevosli Tchéprakoff, 1966, C. spiculigerum (Rudolphi, 1809), C. osculatum (Rudolphi, 1802), C. scotti (Leiper & Atkinson, 1914) and C. pelagicum Johnston & Mawson, 1942b. C. pelagicum is redescribed and turns to be a new rference for Spheniscus magellanicus (Foster).