1 Urosome 1 bearing 3 dorsal teeth or cusps (Fig. 35a).................................. Bathyphotis Stephensen, 1944
– Urosome 1 without dorsal teeth although there may be a pair of short setae (Fig. 35b)............................... 2
2 Pereopods 5–7, ischium posteriorly winged (Fig. 35c). Uropod 3 uniramous, ramus ending in a cluster of spines (Fig. 35e).................................................................................. Alatajassa Conlan, 2007
– Pereopods 5–7, ischium not posteriorly winged (Fig. 35d). Uropod 3 biramous (Fig. 35f)...............................3
3 Pereopods 3–4, propodus prehensile (Fig. 35g)......................................... Isaeopsis K.H. Barnard, 1916
– Pereopods 3–4, propodus rectangular or oval and not expanded distally (Fig. 35h).....................................4
4 Coxa 4 posteriorly excavate (Fig. 35i)........................................................................5
– Coxa 4 not posteriorly excavate (though it may be shallowly concave) (Fig. 35j)......................................7
5 Gnathopod 1, carpus longer than the propodus (carpus:propodus length ~125%). Gnathopod 2, female, propodus massive, length ~175% the length of the propodus of gnathopod 1, palm toothed (Fig. 35k)............. Veronajassa Vader and Myers, 1996
– Gnathopod 1, carpus subequal to or shorter than the propodus (carpus: propodus length ~45–95%). Gnathopod 2, female, propodus not massive, length ~125% the length of the propodus of gnathopod 1, palm not toothed (Fig. 35l)....................6
6 Eyes absent. Maxilla 1, inner plate with a long apical seta (Fig. 36a). Coxa 1 more than half the depth of coxae 2–4. Gnathopod 1, carpus length ~95% the length of the propodus; propodus, palm shallowly excavate (Figs 36c, d)................................................................................................. Myersius Souza-Filho & Serejo, 2014
– Eyes present. Maxilla 1, inner plate without a long apical seta (Fig. 36b). Coxa 1 ± half the depth of coxae 2–4. Gnathopod 1, carpus length ~45–50% the length of the propodus; propodus, palm convex (Figs 36e, f)........... Microjassa Stebbing, 1899
7 Gnathopod 1, carpus ~100% the length of the propodus. Pereopods 3 and 4, dactyl ~175% the length of the propodus (Fig. 36g)................................................................................ Scutischyrocerus Myers, 1995
– Gnathopod 1, carpus shorter than the propodus. Pereopods 3 and 4, dactyl ±90% the length of the propodus (Fig. 36h)........8
8 Uropod 3 with a cluster of distolateral setae beside the outer ramus (Fig. 36i). Jassa group..............................9
– Uropod 3 without a cluster of distolateral setae beside the outer ramus Fig. 36j)......................................13
9 Antenna 1, accessory flagellum absent or scale-like (Fig. 37a)................................ Parajassa Stebbing, 1899
– Antenna 1, accessory flagellum 2 articles, the second minute (Fig. 37b)............................................10
10 Gnathopods and pereopods 3–4 clothed in abundant, long plumose setae (Fig. 3). Gnathopod 2, either sex, propodus, palm bearing a central tooth and a second tooth at the palmar angle, with or without a single large spine at the palmar angle (Fig. 37c)............................................................................................. Plumulojassa n. gen.
– Gnathopods and pereopods 3–4, setae simple or finely pectinate except in the palm of the male gnathopod 2 where the setae may be plumose (Figs 17, 22, 25 and 27– 29). Gnathopod 2, either sex, propodus, palm sinuous, concave or with a pronounced thumb defining the palm proximally, spines if present grouped in triplicate or if single, very small (Figs 37 d–f)..................11
11 Gnathopods 1 and 2, propodus, palm defined by 1 spine. Gnathopod 2 without a gill. Pereopod 5, carpus with a cluster of spines posterodistally. Pleopods, rami very short, length ± depth of the pleon (Figs 22–28)....................... Pleojassa n. gen.
– Gnathopods 1 and 2, propodus, palm defined by multiple spines (usually 3–4). Gnathopod 2 with a gill. Pereopod 5, carpus not spinose posterodistally. Pleopods, rami long, length> depth of the pleon (Fig. 17)....................................12
12 Gnathopod 2, propodus, both sexes producing a thumb at adulthood, palmar defining spines, if present, at the thumb tip (Fig. 37e), juvenile palm sinuous, without a thumb; pereopods 3 and 4, carpus <25% overlapped by the merus; uropod 3, outer ramus with many minute cusps proximal of the dorsally recurved terminal spine but without additional larger cusps (Figs 17–21)............................................................................................. Hemijassa Walker, 1907
– Gnathopod 2, propodus, only the male producing a thumb at adulthood, palmar defining spines, if present, proximal of the thumb tip (Fig. 37f), juvenile palm concave or sinuous, without a thumb; pereopods 3 and 4, carpus 80–100% overlapped by the merus; uropod 3, outer ramus with 2 (usually) larger cusps in addition to minute cusps proximal of the dorsally recurved terminal spine (Figs 35b,d,f,h, 36 h,i and 37f)................................................................ Jassa Leach, 1814
13 Uropods 1, 2 and/or 3, peduncle with lateral row of setae (Fig. 37g)..................... Ruffojassa Vader and Myers, 19961
– Uropods 1, 2 and/or 3, peduncle without a lateral row of setae...................................................14
14 Antenna 1, accessory flagellum 3–4 articles, the last minute. Uropod 3, outer ramus with one to several medial setae projecting dorsally (Fig. 37h)................................................................ Ventojassa J. L. Barnard, 1970
– Antenna 1, accessory flagellum 1–2 articles, the last minute. Uropod 3, outer ramus without medial setae projecting dorsally.........................................................................................................15
15 Gnathopod 1, carpus longer than the propodus (carpus ~120% of the propodus length). Known only from subantarctic islands and Brazil, 44–1058 m......................................................... Pseudischyrocerus Schellenberg, 1931
– Gnathopod 1, carpus shorter than the propodus (carpus ~50–95% of the propodus length). Various locations and depths......16
16 Mandibular palp, article 3 slender, ventrally convex and broadest centrally, tip acute (Fig. 37i). Antennae 1 and 2, length Ξ85% of the body length (headlobe to end of uropods), antenna 2 not stouter than antenna 1. Pereopods 3 and 4, merus not overlapping the carpus anteriorly. Uropod 2, outer ramus, length 65% of the inner ramus....................... Paradryope Stebbing, 18882
– Mandibular palp, article 3 broad distally, end rounded (Fig. 37j). Antennae 1 and 2, length ±65% of the body length (headlobe to end of uropods), antenna 2 stouter than or similar to antenna 1. Pereopods 3 and 4, merus overlapping 10–100% of the carpus. Uropod 2, outer ramus, length 75–80% of the inner ramus.......................................................17
17 Adult male gnathopod 2 grossly lengthened and pendulate, length 190–350% of the length of gnathopod 1, propodus slender, length 180–400% of its width at the centre, dactyl 50–100% of the length of the propodus (Figs 38 a-c). Uropod 3 with 1–2 rows of mid-dorsal spines but without a corona of multiple spines on the distal margin (Fig. 38d). Warm temperate and tropical, Northern and Southern Hemisphere, known from 9– 40°N and 5– 34°S, 0–16 m depth................... Neoischyrocerus Conlan, 1995
– Adult male gnathopod 2 variable in length but not pendulate, length 100–220% of the length of gnathopod 1, propodus variably slender or stout, length 120–290% of its width at the centre, dactyl 33–75% of the length of the propodus (Figs 38 e-g). Uropod 3 with 1–2 rows of mid-dorsal spines and a corona of numerous spines on the distal margin 3 (Fig. 38h). Cold temperate and polar, primarily Northern Hemisphere, known from 36– 81°N and 42°S, 1–2000 m depth............... Ischyrocerus Krøyer, 1838