Holotype DZMB–HH 56285 (ZMH K–46787): 1 ad. 5.5 mm, 61°59.83'–61°59.26 N, 000°30.40'–000°32.32'E, Poseidon IceAGE 2, POS 456, 24.7.2013, Norwegian Channel, North Sea, St. 867, 302.5–290 m depth, EBS Supra, 300 μm. In alcohol.

All in alcohol; one slide DZMB-HH52415.

DZMB–HH 52177 (ZMH K–46788): juv. 2 mm; 61°53.79'N–61°53.53'N, 010°13.77'W–010°12.65'W, Poseidon IceAGE 2, POS 456, 29.7.2013, FI Ridge, St. 878–1, 781.4–775.8 m depth, EBS Supra, 300 μm.

DZMB–HH 52021(ZMH K–46789): 1 es. 4 mm; 60°24.33'N–60°23.70'N, 006°36.91'–006°38.60'W, Poseidon IceAGE 2, POS 456, 29.7.2013, Farøer Channel South-East, St. 876–5, 554.3–674.8 m depth, shell fragments, EBS, 500 μm.

DZMB–HH 52593 (ZMHK–46790): 8 es. 3–4 mm; 61°53.79'N–61°53.53'N, 010°13.77'W–010°12.65'W, Poseidon IceAGE 2, POS 456, 29.7.2013, FI Ridge, St. 878–1, 781.4–775.8 m depth.

DZMB–HH 52617(ZMH K–46791): 1 juv. 2.5 mm; 63°42.53'N–63°42.78'N, 026°23.05'–026°22.53'W, Meteor IceAGE, ME 85–3, 9.9. 2011, South Iceland, Irminger Basin, slope, St. 1086–1, 698.1– 678.5 m depth, 730 trawling distance, EBS Supra, 300 μm.

DZMB–HH 52667 (ZMH K–46792): 1 juv. incompl., 2 mm: 61°38.50'N–61°39.24'N, 031°21.37'–031°20,95'W, Meteor IceAGE, ME 85–3, 7.9.2011, South Iceland, Irminger Basin, Deep Sea, St. 1057–1, 2504.7–2531.8 m depth, 1983 trawling distance, EBS Supra, 300 μm.

DZMB–HH 52694 (ZMH K–46793): 3 juv. 2–3 mm; 60°24.33'N–60°23.70'N, 006°36.91'–006°38.60'W, Poseidon IceAGE 2, POS 456, 29.7.2013, Farøer Channel South-East, St. 876–5, 554.3–674.8 m depth, shell fragments, EBS, 500 μm.

DZMB–HH 52415 (ZMH K–46794): 2 es. 2-3 mm; 63°42.10'N–63°42.37'N, 026°23.64'–026°23.46'W, Meteor IceAGE, ME 85–3, 9.9.2011, South Iceland, Irminger Basin, slope, St. 1082–1, 724.4–704.9 m depth, 782 trawling distance, EBS Supra, 300 μm. Slide in Faure’s medium, used for illustration.

Eyes oval, dark in ethanol. Mandibular palp long and narrow, art 3 more than half the length of art 2. Cx 1 inferior margin smooth, nearly as long as wide. Gn 1 carpus distal part approximately six times longer than wide, dactylus reaching approximately 1/3 of propodus length. P 3, P 4 with narrow basis, P 5 – P 7 basis oval and broadened, with regularly rounded and finely serrated hind margin. Ep 2 posterodistally with upturned tip, Ep 3 distoposterior corner with blunt, rounded angle.

Length 4–6 mm.

Head. Anterior margin rounded, anterodistal margin rectangular with rounded corner. Mid-cephalic keel with acute projection. Rostrum small.

Eyes oval. Antennae short, nearly 1/3 of body length, A 1 peduncle art 1 inferodistally with acute tooth, flagellum up to 11 arts, accessory flagellum not seen. A 2 subequal in length to A 1, peduncle art 4 > art 5, flagellum around 6 arts.

Mouthparts. Mandible lacking molars, palp 3-articulate, with long lateral and single distal setae. Art 3 with distal seta, incisors strongly dentate. Other mouthparts like in L. spinicarpa.

Peraeon. Cx 1– Cx 4 relative width 1: 1.2:0.8:1.

Coxa 1 smooth, length and width subequal; anterodistal margin produced, distal margin regularly rounded, facial setae absent.

Gn 1 basis not inflated, carpus distal part narrow, length to width ratio approximately 6:1; propodus straight, palm with fine short spines; dactylus curved, reaching nearly 1/3 of propodus length.

Cx 2 nearly as long as wide, subquadrangular, much wider than Cx 3, smooth; facial setae absent.

Gn 2 basis slightly inflated, on anterior margin some setae of different length; carpus reaching approx. half propodus, distally truncate, setose; propodus distally with short, sharp prolongation, palm convex, regularly rounded, with weak mediofacial setal row, with a few submarginal setae; dactylus curved, smooth, reaching more than 2/3 of propodus length.

Cx 3 length greater than its width, smooth, subrectangular with straight margins and rounded corners.

Cx 4 wider than Cx 3, posterior margin shorter than anterior one, somewhat excavate.

P 3, 4 basis narrow, approx. the width of merus; dactylus reaching or surpassing half the length of propodus.

P 5 – 7 similar, basis oval, both margins with fine serration.

Pleon. Ep 1 posteroventral corner rounded. Ep 2 posterodistal corner acutely produced, Ep 3 posteroventral corner bluntly rounded.

U 1 – U 3 similar, length regularly diminishing and U 2 not considerably shorter (like in L. spinicarpa).

Wim Vader completed eight decades in February 2017. He was born Dutch but having lived for much more than half of his life in Norway, he will easily guess that I used the Norwegian word åtti = eighty for dedicating this Atlantic species to him. Fifty years ago we began our long-lasting and harmonious collaboration, a “golden jubilee”- thank you, Wim!

South Iceland- Farøer Channel and Ridge; depth 554–2531 m.

Together with five specimens collected 1983 between Greenland and Iceland (see Krapp-Schickel and Vader 2012) the present material of the proposed new species consists of 23 animals belonging undoubtedly to the genus Leucothoe. All specimens are between 2 and 5 mm, rarely up to 6 mm long. There are four specimens larger than 10 mm with all characters fitting Leucothoe spinicarpa, sampled in similar depths as those of the animals 2–5 mm in size. The larger specimens show some differences which are not very conspicuous. It is most probable that they belong to two different species, and it seems also quite reasonable to presume that within the period of early June to end of September these 23 specimens are not all juveniles; however, no ovigerous females were found.

Differences of the small animals compared with Leucothoe spinicarpa are:

• Ep 3 totally blunt (see here fig. 2 and Krapp-Schickel and Vader 2012: 390 fig. 4 Ep3) vs. not rounded, but with small but clear posterodistal corner in L. spinicarpa (Crowe 2006: 61 fig. 1a, 63 fig. 3e; Sars 1885 pl. 101)

• U 2 in adults reaching length of U1 (see fig. 2) vs. clearly much shorter than U1 and U3 in L. spinicarpa (Crowe 2006 fig. 1 and fig. 4)

• Gn 1, 2 basis anterior margin with few irregular longer or shorter setae (see here fig. 1, Krapp-Schickel and Vader 2012: 389 fig. 3) vs. dense setation in L. spinicarpa (Crowe 2006 fig. 61 fig. 1 b–e; Sars 1895 pl. 100)

• Gn 1 dactylus less than half the length of propodus (see above fig. 1; Krapp-Schickel and Vader 2012: 389 fig. 3) vs. more than half the length of propodus in L. spinicarpa (Crowe 2006 fig. 61 fig 1c; Sars 1885 pl. 100)

• sizes of 23 specimens collected between 1 June–30 September are all between 2–4 mm, with only a few reaching 6 mm; vs. size range between 10–19 mm of L. spinicarpa (Crowe 2006, Sars 1895, Krapp-Schickel and Menioui 2005).

These differences are significant enough to distinguish these small specimens as a new species.

Two other Leucothoe species were sampled, L. spinicarpa and L. lilljeborgi, the latter clearly in lower depths than the new species.

DZMB–HH 56264 (ZMH K–46795): 1 spec. 2.5 mm Leucothoe lilljeborgi 61°25.63'–61°25.05'N, 001°21,07'–001°21.66'E, Poseidon IceAGE 2, POS 456, 24.07.2013, Norwegian Channel, North Sea, St. 866, 169.1–168.8 m depth, EBS Epi, 500 μm.

DZMB–HH 56326 (ZMH K–46796): 2 spec. 2–2.5 mm L. lilljeborgi 61°25.63'–61°25.05N, 001°21.07'–001°21.66'E, Poseidon IceAGE 2, POS 456, 24.7.2013, Norwegian Channel, North Sea, St. 866, 169.1–168.8 m depth, EBS Epi, 300 μm decant.

DZMB–HH 56428 (ZMH K–46797): 1 spec. 2.5 mm L. lilljeborgi: 61°25.63'–61°25.05N, 001°21.07'–001°21.66'E, Poseidon IceAGE 2, POS 456, 24.7.2013, Norwegian Channel, North Sea, St. 866, 169.1–168.8 m depth, EBS Epi, 300 μm.

DZMB–HH 56500 (ZMH K–46798): 1 L. spinicarpa 13 mm, 2 males L. lilljeborgi 5.5 and 4 mm 61°59.83'–61°59.26N, 000°30.40'–000°32.32'E, Poseidon IceAGE 2, POS 456, 24.7.2013, Norwegian Channel, North Sea, St. 867, 302.5–290 m depth, EBS Epi, 500 μm.

DZMB–HH 52362 (ZMH K–46799): 1 L. spinicarpa 11 mm; 63°42.53'N–63°42.78'N, 026°23.05'–026°22.53'W, Meteor IceAGE, ME 85-3, 9.9.2011, South Iceland, Irminger Basin, slope, St. 1086-1, 698,1–678.5 m depth, 730 trawling distance, EBS Supra, 300 μm.

DZMB–HH 52627 (ZMH K–46800): 1 L. spinicarpa 8 mm 62°33.10'N–62°33.22'N, 020°23.71'–020°22,87'W, Meteor IceAGE, ME 85-3, 2.9.2011, South Iceland, Iceland Basin, slope, St. 1010–1, 1384.8–1389 m depth, 1183 trawling distance, EBS Supra, 300 μm.

DZMB–HH 32864 (ZMH K–46801): 1 juv. Leucothoe sp. imperf. 2 mm, together with Leucothoe spinicarpa 12 mm; 61°53.79'N–61°53.53'N, 010°13.77'W–010°12.65'W, Poseidon IceAGE 2, POS 456, 29.7.2013, FI Ridge, St. 878-1, 781.4–775.8 m depth, EBS Supra, 300 μm.