Abstract
Agathotanaisis one of the seven genera classified into the family Agathotanaidae. So far, 12 species have been described for the genus, seven of which are known from the Pacific. However, considering the present poor state of knowledge on deep-sea environments, a much higher number ofAgathotanaisspecies than currently known can be suspected. Among the studied material, collected from below 1,000 m during five deep-sea expeditions in different parts of the Pacific Ocean, we identified eight species: two of them were already known to the science and five species were identified as new to knowledge and their formal description is presented in the paper: two from the North West Pacific (the Sea of Okhotsk and Kuril-Kamchatka Trench), two from the Central Pacific (Clarion-Clipperton Fracture Zone), and one from the Australian slope. The eighthAgathotanaisspecies in our material was determined using a molecular approach, but it was represented by only one partially destroyed individual and could therefore not be formally described. The proportion ofAgathotanaiscollected at the Sea of Okhotsk was the highest (22%), whereas the numbers were substantially lower for the Kuril-Kamchatka Trench, and the Central and the Southern Pacific. Molecular analyses confirmed the monophyly ofAgathotanaisandParagathotanaisand a close relationship between both genera. Moreover, a close relationship between the two Australian species was revealed. As a result of our findings, the number of species known from the Pacific increased from 5 to 11, with the total number of species in this genus increasing from 12 to 17. An updated identification key forAgathotanaisspecies is given.
Highlights
Genus Agathotanais was established to allocate Agathotanais ingolfi Hansen, 1913, discovered off Iceland during the Danish Ingolf Expedition (Hansen, 1913)
Using morphological and genetic tools, we present the description of five new species of Agathotanais collected from four areas of the Pacific: ClarionClipperton Fracture Zone, off East Australia, the Sea of Okhotsk, and the KurilKamchatka Trench (KKT)
A total of 736 specimens of Agathotanais were classified into eight species, five of which were new to science: A. beatae n. sp., A. frutosae n. sp
Summary
Genus Agathotanais was established to allocate Agathotanais ingolfi Hansen, 1913, discovered off Iceland during the Danish Ingolf Expedition (Hansen, 1913) It was described and marked as the most aberrant among all tanaids due to its rudimentary antenna, cheliped attached directly to the cephalothorax, the appearance of the pleopods in juvenile males (Hansen, 1913), and the setulose surface of its body (Larsen, 2005; Józwiak and Jakiel, 2012; Kakui and Kohtsuka, 2015). The history of the exploration of Pacific deep-sea regions started in the XIX century with the HMS Challenger expedition (1872–1876), during which the polymetallic nodules and the Mariana Trench were discovered (Schofield, 2018). Six new species belonging to genus Agathotanais were added to the list of Pacific agathotanaids, namely: Agathotanais hadalis Larsen, 2007 from the North West Pacific abyssal, Agathotanais misakiensis Kakui and Kohtsuka, 2015 and Agathotanais toyoshioae Kakui and Kohtsuka, 2015 from the coast of Japan, Agathotanais spinipoda Larsen, 1999 from the slope of Bass Strait, and Agathotanais manganicus Larsen, 1999 and Agathotanais ahyongi Larsen, 1999 from the Central Pacific abyssal (Larsen, 1999, 2007; Kakui and Kohtsuka, 2015)
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