Two new hadal amphipod species (Lysianassoidea: Uristidae) with notes on their reproductive strategies

Abstract

Amphipods of the family Uristidae Hurley, 1963 are geographically widespread scavengers found globally from shallow waters to hadal (> 6000 m) depths. This study utilises integrative taxonomy to describe two new Uristid species, sampled exclusively from hadal depths within two geographically discrete features. Galathella ovaimmensa sp. nov. was collected from the South Sandwich Trench (Southern Ocean) and is placed into the genus based on key morphological features including the tapering coxa 1 and the rounded sub-acute lateral cephalic lobe. Profundum solomoni gen. nov. sp. nov. was collected from the Santa Cruz and San Cristobal trenches (Southwest Pacific Ocean) yet did not morphologically correspond to any genera within the family Uristidae, prompting the description of the new genus Profundum gen. nov. Both new species were collected here with high proportions of brooding females. The reproductive strategies of amphipods living deeper than 6000 m are poorly characterised, mainly due to the challenge of sampling brooding females. The brood size of Galathella ovaimmensa sp. nov. ranged from 1 to 7 (median = 3, n = 169), compared to Profundum solomoni gen. nov. sp. nov. whose brood size ranged from 7 to 30 (median = 15, n = 50). Brood morphometrics were further investigated using micro-computed tomography. Egg volume of Galathella ovaimmensa sp. nov. was relatively large, ranging from 0.402 to 0.884 mm 3 compared to the egg volume of Profundum solomoni gen. nov. sp. nov. which was smaller, ranging from 0.102 to 0.255 mm 3 .

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