Cephalopods are an important component of Southern Ocean food webs but studies analysing their habitat and trophic ecology are scarce. Here, we use the Antarctic toothfish Dissostichus mawsoni as a biological sampler of Southern Ocean's cephalopods in the Ross, Amundsen, and D'Urville Seas. Ten cephalopod taxa were identified in the diet of the Antarctic toothfish, with Pareledone turqueti and Moroteuthopsis longimana being the only species present in all the three studied areas. DNA analysis conducted on squid flesh samples allowed identification of eight and two specimens of Mesonychoteuthis hamiltoni and M. longimana, respectively, proving this technique as a potential tool to improve the knowledge of cephalopods biodiversity and biogeography in the Southern Ocean. Stable isotopes were used to compare the habitat (δ¹³C) and trophic ecology (δ¹⁵N) between two life-stages of the two most abundant squid species (M. longimana and Psychroteuthis glacialis) from the D'Urville Sea (both squid species) and Amundsen Sea (only P. glacialis). Higher δ¹³C values in M. longimana suggest that this species inhabits waters near the Antarctic Polar Front, with incursions into sub-Antarctic waters, whilst P. glacialis spends its entire life in Antarctic waters. The most recently deposited part of the beak is enriched in ¹⁵N suggesting an increase in trophic level during squid growth. These results give us the first insights into the bathyal distribution of cephalopods in the Amundsen and D'Urville Seas, as well as into the ontogenetic changes of two of the most consumed squid species by top predators in this region. Such results are an important step towards improving the biogeography of Antarctic cephalopods, being of utmost importance to understand the biodiversity, food web structure, and functioning of this region.

头足类动物是南大洋食物网的重要组成部分，但对其栖息地和营养生态进行分析的研究很少。在这里，我们使用南极牙鱼Dissostichus mawsoni作为罗斯海、阿蒙森海和德维尔海中南大洋头足类动物的生物采样器。在南极牙鱼的饮食中发现了 10 种头足类动物分类群，Pareledone turqueti和Moroteuthopsis longimana是所有三个研究区域中唯一存在的物种。对鱿鱼肉样本进行的 DNA 分析允许鉴定出八个和两个Mesonychoteuthis hamiltoni和M. longimana标本分别证明该技术是提高南大洋头足类生物多样性和生物地理学知识的潜在工具。稳定同位素被用来比较来自德维尔海的两种最丰富的鱿鱼物种（M. longimana和Psychroteuthis glacialis）的两个生命阶段的栖息地 ( δ ¹³ C) 和营养生态学 ( δ ¹⁵ N)。种）和阿蒙森海（仅P. glacialis）。M. longimana 中较高的δ ¹³ C 值表明该物种栖息在南极极地前沿附近的水域，并侵入亚南极水域，而P. glacialis一生都在南极水域度过。喙最近沉积的部分富含¹⁵ N，表明在鱿鱼生长过程中营养水平增加。这些结果使我们首次了解了阿蒙森海和德维尔海中头足类动物的深海分布，以及该地区顶级捕食者消耗最多的两种鱿鱼物种的个体发育变化。这些结果是改善南极头足类生物地理学的重要一步，对于了解该地区的生物多样性、食物网结构和功能至关重要。