|Abstract: ||Abstract:Members of the deep-sea caridean shrimp genus Leontocaris Stebbing, 1905(family Hippolytidae Spence Bate, 1888) have a very peculiar major secondcheliped with a massive palm bearing a tympanum and a blade-like dactylus,probably related to an as yet unknown predatory behaviour (Taylor & Poore,1998; Fransen, 2001; Poore, 2009). Currently nine species are known in thegenus (De Grave & Fransen, 2011; Cardoso & Fransen, 2012). In North Atlanticwaters only one species, Leontocaris lar Kemp, 1906 has been reported and upto now, remains only known from three specimens collected off Ireland morethan a century ago (Kemp, 1906, 1910; d’Udekem d’Acoz, 1999). The rarity ofthis species, and indeed all known species in the genus, is likely due to theseshrimps inhabiting deep-sea coralline habitats, which are very difﬁcult to sampleby conventional means (Kemp, 1906, 1910; Taylor & Poore, 1998; Fransen,2001; Poore, 2009; Ahyong, 2010; Cardoso & Fransen, 2012). In 2011, duringa ROV “Victor6000” dive of the “BobEco” cruise carried out on board the RV“Pourquoi Pas?” (chief scientist: S. Arnaud-Haond, Ifremer), a further specimenwas collected in the Celtic Sea off north-western France, allowing for a betterunderstanding on the characteristics and ecology of this rare species. In situobservation of L. lar conﬁrms for the ﬁrst time its association with antipathariancorals. A close examination of the present specimen reveals that the recentlydescribed Leontocaris smarensis Cardoso & Fransen, 2012, from the South Mid-Atlantic Ridge is extremely similar to L. lar, potentially being a synonym of L. lar.
The specimen described in this work is deposited in the collection of theMuséum National d’Histoire Naturelle, Paris (MNHN). Carapace length (cl) ismeasured dorsally from the posterior part of the orbit to the posterior margin of thecarapace.