Ischyrocerini, Kroyer, 1838

Conlan, Kathleen E., 2021, New genera for species of Jassa Leach (Crustacea: Amphipoda) and their relationship to a revised Ischyrocerini, Zootaxa 4921 (1), pp. 1-72 : 61-62

Key to genera of the Ischyrocerini

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

Figures

FIGURE 3. Plumulojassa ocia (Bate, 1862). Neotype, male 1, 3.5 mm. West side of St. Warna’s Cove, St. Agnes, Scilly Isles, Cornwall, England, 1 August 1973, P. Parslow, coll., NHM 1987:514. Male 2, 3.0 mm and male 3, 3.7 mm, Le Croisic, France, date unknown, E. Chevreux, coll., MNHN Am. 2664. Setae are omitted from the gnathopod 2 profiles of males 2 and 3. All views lateral. Scale 0.1 mm.

FIGURE 17. Hemijassa goniamera (Walker, 1903). Lectotype, male, 18.3 mm, and paralectotype, male 1, 6.1 mm, Cape Adare, McMurdo Sound, Ross Sea, Antarctica, 10, 14 and 26 November 1899, Southern Cross Expedition, NHM 1987:515. Lateral view: whole body; dorsal view: telson; other views medial. Scale 0.1 mm.

FIGURE 22. Pleojassa moorei n. sp. Holotype, male 1, 4.0 mm (NHM 1987:511), allotype, female 1 (NHM 1987:512), 4.25 mm and paratype, male 2, 3.25 mm. Billie Rocks, Signy Island, South Orkney Islands, 4 March 1965, M. H. Thurston, coll., NHM 1969:768:ca. 430, station no. 13(244). Male 3, 3.4 mm, male 4, 3.6 mm, male 5, 3.4 mm, and female 2, 4.2 mm, Billie Rocks, Signy Island, South Orkney Islands, 3 March 1965, M. H. Thurston, coll., CMN IZ1989-013, 1969:771:ca 260 (pt.), station no. 16(333). Most setae are omitted from the gnathopod 2 profiles. Lateral views: whole body, male 3 antenna 1, uropod 3 and gnathopod 2 profiles; dorsal view: uropod 1 and telson; medial views: male 5 antenna 1 and female 2 gnathopod 2. Scale 0.1 mm.

FIGURE 25. Pleojassa lowryi n. sp. Holotype, male, 5.3 mm, allotype, female, 4.6 mm and paratypes, male 1, 2.9 mm and male 2, 4.3 mm. Rima Islet, The Snares, New Zealand, 21 November 1976, G. D. Fenwick, coll., AM P.34948, station no. SA-3417. Setae are omitted from the second gnathopod profiles. All views lateral. Scale 0.1 mm.

FIGURE 27. Pleojassa multidentata (Schellenberg, 1931). Male, 8.0 mm and male 1, 7.4 mm. South Georgia, Swedish Antarctic Expedition (1901–1903), collection date and collector unknown, MfN 22.962. Male 2, paralectotype, 3.7 mm and adult female, lectotype, 7.7 mm. South Georgia, 1883, Deutsche Polar Commission, K. von den Steinen, coll., ZMH K-8028. Setae are omitted from the gnathopod 2 profiles of the male 1 and male 2. All views lateral. Scale 0.1 mm.

FIGURE 28. Pleojassa orientalis n. sp. Holotype, adult female, 9.8 mm and male, paratype, ~6.5 mm (full length estimated from comparison with the female as body posterior to segment 4 missing). Southeast corner of Gorilla Head Rock, Macquarie Island, Australia (54°29ʹS, 158°58ʹE), 23 December 1977, J. K. Lowry, coll., AM P.34955, station no. MA-147. Setae are omitted from the male gnathopod 2 profile. All views lateral. Scale 0.1 mm.

FIGURE 29. Pleojassa wandeli (Chevreux, 1906). Lectotype, male, 6.0 mm. Ile Booth-Wandel, Antarctica, 10 December 1904, Expédition Antarctique Française (1903–1905), MNHN Am. 2630(1). Lateral view: whole body; dorsal view: telson; other views medial. Scale 0.1 mm.

FIGURE 35. a. Bathyphotis tridentata after Stephensen (1944); b. Jassa falcata from Conlan et al. (in press); c. Alatajassa similis after Conlan (2007); d. Jassa falcata from Conlan et al. (in press); e. Alatajassa similis after Conlan (2007); f. Jassa falcata from Conlan et al. (in press); g. Isaeopsis tenax after K.H. Barnard (1916); h. Jassa falcata from Conlan et al. (in press); i. Microjassa bahamensis after Conlan (1995); j. Neoischyrocerus lilipuna after Conlan (1995); k. Veronajassa neptunea after Vader and Myers (1996); l. Myersius denticaudatus after Souza-Filho and Serejo (2014). Scale 0.1 mm.

FIGURE 36. a. Myersius denticaudatus after Souza-Filho and Serejo (2014); b. Microjassa cumbrensis after Conlan (1995); c. Myersius denticaudatus after Souza-Filho and Serejo (2014); d. magnification of c (palm only); e. Microjassa floridensis after Conlan (1995); f. magnification of e (palm only); g. Scutischyrocerus scutatus after Myers (1995); h. Jassa marmorata from Conlan et al. (in press); i. Jassa oclairi from Conlan et al. (in press); j. Pseudischyrocerus denticaudata after Schellenberg (1931). Scale 0.1 mm.

FIGURE 37. a. Parajassa pelagica after Sars (1894); b. Jassa thurstoni from Conlan et al. (in press); c. Plumulojassa ocia from FIGURE 3; d. Pleojassa lowryi from FIGURE 25; e. Hemijassa goniamera from FIGURE 17; f. Jassa falcata from Conlan et al. (in press); g. Ruffojassa festa after Vader and Myers (1996); h. Ventojassa frequens from FIGURE 10; i. Paradryope orguion after Stebbing (1888); j. Neoischyrocerus lilipuna after Conlan (1995). Scale 0.1 mm.

FIGURE 38. a. Neoischyrocerus lilipuna after Conlan (1995); b. Coxischyrocerus rhombocoxus after Just (2009); c. Tropischyrocerus pugilus after Just (2009); d. Neoischyrocerus claustris after Conlan (1995); e. Ischyrocerus anguipes after Sars (1894); f. Ischyrocerus megacheir after Sars (1894); g. Ischyrocerus megalops after Sars (1894); h. Ischyrocerus anguipes after Sars (1894). Scale 0.1 mm.