The hippolytid genus Leontocaris includes eight species, all restricted to the deep sea (240–2182 m). Associations with deep sea coralline habitats were reported and are herein confirmed. Three Australian species were recorded at seamounts as were the specimens herein identified as L. smarensis sp. nov. These specimens were sampled at the South Mid-Atlantic Ridge (SMAR) by the Mar Eco project during 12 bottom trawls using a Sigsbee trawl. The SMAR is a seamount chain that rises from 4000 m depth, with mountains of 100–200 km wide and 14,000 km length. Leontocaris smarensis sp. nov. shows closest affinity to L. lar from the north-western Atlantic and L. yarramundi, from Australia and New Zealand. It differs from L. lar mainly in: (1) the scaphocerite distolateral tooth reaching the distal margin of the blade while clearly falling short in the latter species; and (2) the mandibular palp possessing three distal setae while setae are absent in L. lar. The new species differs from L. yarramundi in the number and disposition of dorsal teeth on rostrum and in the absence of an acute posterolateral spine on abdominal somites 4 and 5.