Jassa , Vader & Krapp 2005
Creators: name: Conlan, Kathleen E.
name: Desiderato, Andrea
name: Beermann, Jan
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Amphipoda
Ischyroceridae
Jassa

description: Key to the world species of Jassa (both sexes) 6
1 Gnathopod 2, basis, at least the distal part of the anterolateral margin bearing a fringe of setae (at least some setal lengths 20–40% or more of the maximal basis width) (e.g., Figs 15, 28, 78, 88 and 102) (fringe alsopresent in juveniles but may be less pronouncedthanin adults...e.g., see Fig. 102) ............................................................... 2
- Gnathopod 2, basis, setae short, minute or absent (setal lengths <20% of the maximal basis width) (e.g., Figs 37, 85, 95 and 104)............................................................................................... 13
2 Gnathopod 2, propodus, anteroproximal margin with a row of long setae (setal length Ẑthe maximal basis width). Gnathopod 1, carpuswithoutasetaorclusterofsetaeattheanterodistaljunctionofthepropodus (Figs 67 and 68) ... J. staudei Conlan, 1990
- Gnathopod 2, propodus, setae on the anteroproximal margin short or absent (setal length <65% of the maximal basis width). Gnathopod 1, carpus, seta(e) at the anterodistal junction of the propodus present or absent (may be slightly medial or lateral and aslongasthecarpusorveryshort) (e.g., Figs 15, 22, 65 and 88–90) ................................................3
3 Gnathopod 2, female, palmsinuous (e.g., Figs 88, 97 and 102).....................................................4
- Gnathopod 2, female, palmconcave (e.g., Figs 15, 26, 29 and 65)..................................................6
4 Gnathopod 1, basis, anterior margin with a row of spine-like setae; carpus, anterodistal margin with a single or cluster of setae at thejunctionof thepropodus (Figs 88–90) ................................................. J. alonsoae Conlan, 1990
- Gnathopod 1, basis, anteriormarginwithoutarowof spine-likesetae (Figs 85 and 102) ................................5
5 Gnathopod 1, carpus, anterodistal margin with a seta or cluster of setae at the anterodistal junction of the propodus (seta(e) ~40% thelengthof the carpus) (Fig. 85) ......................................................... J. myersi Conlan, 19907
- Gnathopod 1, carpus, anterodistal margin without a seta or cluster of setae at the junction of the propodus (Fig. 102).......... .................................................................................... J. gruneri Conlan, 1990
6 Uropod 1, peduncular spinous process that extends ventrally from the peduncle and underlies the rami very short (±10% of the lengthof thelongest ramus) (Fig. 65) ................................................... J. borowskyae Conlan, 1990
- Uropod 1, peduncular spinous process that extends ventrally from the peduncle and underlies the rami at least 25% to 50% the lengthofthelongestramus (e.g., Figs 42, 88 and 99) ............................................................7
7 Gnathopod 1, carpus with a seta or cluster of setae at the anterodistal junction of the propodus (seta or setal cluster may be slightly lateralormedialandshortoraslongasthe carpus) (e.g., Figs 15, 22, 29, 31, 62 and 81) ................................8
- Gnathopod 1, carpuswithoutasetaorclusterofsetaeattheanterodistaljunctionofthepropodus ... J. monodon (Heller, 1866)
8 Gnathopod 1, carpus, seta or cluster of setae at the anterodistal junction of the propodus short (length <25% of the length of the carpus) andslightlymedialorlateral (Figs 15 and 31)............................................................9
- Gnathopod 1, carpus, seta or cluster of setae at the anterodistal junction of the propodus long (length 25–50% of the length of the carpusor longer) andslightlymedialorlateral (Figs 22, 29, 62 and 81).............................................10
9 Telson, tip bearing a seta or setae extending between the third uropods (these setae are in addition to the usual upright setae at each lateral cusp and are visible when the uropods are pressed downwards and away from the telson). Antenna 2, thumbed males and adult females of any size without plumose setae on the posterior margin of article 5 and the flagellum (though setae may look finely pectinate). Gnathopod 2, propodus of major form thumbed male, thumb conical, tip acute, spine or spine group on the posteriormarginattheoriginof thethumbabsent (character statesdifferintheminor form) (Figs 31–33) ................... ..................................................................................... J. valida (Dana, 1853)
- Telson, tip without apical setae (though the usual upright setae at each lateral cusp are present). Antenna 2, large thumbed males and adult females, with dense plumose setae on the posterior margin of article 2 and the flagellum. Gnathopod 2, propodus of major form thumbed male, thumb wide, tip squared, spine or spine group on the posterior margin at the origin of the thumb absent (character statesdifferintheminor form) (Figs 15–16)..................................... J. marmorata Holmes, 1905
10 Gnathopod 2, basis and propodus, anterior marginal setae abundant and plumose (Figs 62–63). Mandibular palp, article 2, with a fringeof setaeonthedorsalmargin (Fig. 64) ................................................. J. oclairi Conlan, 1990
- Gnathopod 2, basis and propodus, anterior marginal setae sparse and simple (Figs 22, 28 and 78). Mandibular palp, article 2, withoutafringeofsetaeonthedorsalmargin (Figs 27, 30 and 82) ................................................11
11 Telson, tip bearing apical seta or setae in addition to the usual upright seta or setae at each lateral cusp (Fig. 28).............. .................................................................................... J. morinoi Conlan, 1990
- Telson, tipwithoutapical setae, onlywiththeusualuprightsetaorsetaeateachlateralcusp (Figs 22 and 78) ..............12
12 Antenna 2, large thumbed male and large adult female, peduncular article 5 and flagellum, posterior margin bearing dense plumose setae (Figs 22 and 23). Gnathopod 2, propodus of major form male, thumb tip acute; spine or spine group on the posterior margin at the origin of the thumb absent (although present in small thumbed males) (Figs 22 and 23). Gnathopod 1, female propodus, palm straight to shallowly concave. Gnathopod 2, female propodus, maximum width about 50% of maximum length, palmar anglenotclosetothedefining spines; spinestightly clustered (Fig. 26) ........................... J. slatteryi Conlan, 1990
- Antenna 2, thumbed male and large adult female, peduncular article 5 and flagellum setae not plumose (though may be microscopically pectinate) (Fig. 81). Gnathopod 2, propodus of major form male, thumb tip angled posteriorly, spine or spine group on the posterior margin at the origin of the thumb present (Fig. 78). Gnathopod 1, female propodus, palm convex. Gnathopod 2, female propodus, maximum width about 65% of maximum length, palmar angle close to the defining spines; spines sequential
6 This key is limited by incomplete knowledge of J. kimi, J. laurieae, J. monodon and J. shawi. Sufficient information for J. kimi, J. monodon and J. shawi allow for their inclusion but Jassa laurieae has been excluded because its characteristics are unknown posterior of pereon segment 4. See Table 11 and Remarks section for J. laurieae for distinguishing character states.
7 J. myersi appearstwiceinthekeybecausethesetalfringeontheanterolateralmarginofthebasisofgnathopod 2 canbe interpreted as being present or absent due to the sparseness of the setae on some individuals
(Fig. 81) ............................................................................. J. carltoni Conlan, 1990
13 Uropod 1, peduncular spinous process that extends ventrally from the peduncle and underlies the rami short (<10% of the length of thelongest ramus) (e.g., Figs 65 and 83). Onlyknownfromthe Northeastern Pacific................................14
- Uropod 1, peduncular spinous process that extends ventrally from the peduncle and underlies the rami at least 25% to 50% the lengthofthelongestramus) (e.g., Figs 42, 88 and 99). Notknownfromthe Northeastern Pacific ........................15
14 Gnathopod 1, carpus, seta or setal cluster at the anterodistal junction of the propodus about 35% of the length of the carpus. Gnathopod 2, female propodus, palmsinuous (Fig. 85) ............................................ J. myersi Conlan, 1990
- Gnathopod 1, carpus, seta or setal cluster at the anterodistal junction of the propodus minute (<15% of the length of the carpus) and slightly medial. Gnathopod 2, female propodus, palm concave, palmar defining angle acute and close to the defining spines (Fig. 83) ............................................................................... J. shawi Conlan, 1990
15 Pereopods 5–7, anterior margin of the propodus, spines strong and spine row extending half or more of its full length, propodus expandedornotexpanded forgrasping (Figs 92, 95 and 99). .....................................................16
- Pereopods 5–7, anterior margin of the propodus, spines mostly on the distal half, propodus not expanded for grasping (e.g., Figs 42, 48, 93 and 96)........................................................................................18
16 Gnathopod 1, carpus, seta or setal cluster at the anterodistal junction of the propodus about 1/3 the length of the carpus and slightly lateral and medial. Body length at maturity 15–25 mm (thumbed males and females with setose brood plates) (Fig. 99)........ .................................................................................... J. ingens (Pfeffer, 1888)
- Gnathopod 1, carpus without a seta or setal cluster at the anterodistal junction of the propodus. Body length at maturity 5–9 mm (thumbedmalesandfemaleswithsetosebroodplates) (Figs 92 and 95) ............................................17
17 Pereopods 5–7, anterior margin of the propodus expanded proximally for grasping. Antenna 2, thumbed male, posterior margin of article 5 andflagellumdenselyclothedinplumose setae. Gnathopod 2, female, palmof thepropodussinuous (Fig. 95) ........ .................................................................................... J. fenwicki Conlan, 1990
- Pereopods 5–7, anterior margin of the propodus not expanded proximally for grasping. Antenna 2, thumbed male, posterior margin of article 5 and flagellum without plumose setae (though setae are minutely barbed). Gnathopod 2, female, palm of the propoduswithadistinctledgedistalof thepalmardefiningspines (Fig. 92) .......................... J. justi Conlan, 1990
18 Gnathopod 1, carpus with a seta or setal cluster at the anterodistal junction of the propodus (length about 25% of the carpus length) (Fig. 93)............................................................................ J. thurstoni Conlan, 1990
- Gnathopod 1, carpus without a short seta or setal cluster at the anterodistal junction of the propodus (e.g., Figs 42–43), or if seta present, length <15% of thecarpuslength (e.g., Figs 60 and 96). ..................................................19
19 Mandibular palp, article 2 withafringeof setaeonthedorsalmargin (Figs 47 and 53) ................................20
- Mandibular palp, article 2 withoutafringeofsetaeonthedorsalmargin (Figs 41, 61 and 98) ...........................21
20 Uropod 3, inner ramus bearing 1 or 2 spines centrally in addition to the usual spine at the tip (Fig. 42). Antenna 2, large adult male and female, posterior margin of peduncular article 5 and flagellum article 1 bearing dense plumose setae (Figs 42–43) (these absentinsmall juveniles). Gnathopod 2, female propodus, palmarangle bulbous, distantfromthedefiningspines (Fig. 44). .... .................................................................................. J. falcata (Montagu, 1808)
- Uropod 3, inner ramus without central spines (only the usual spine at the tip) (Fig. 48). Antenna 2, large adult male and female, posterior margin of peduncular article 5 and flagellum article 1 without plumose setae (Fig. 48) (although setae may be minutely barbed) (Fig. 50). Gnathopod 2, female propodus, palmarangle acute, close tothedefining spines (Figs 51 and 52) ........... ................................................................................. J. herdmani (Walker, 1893)
21 Gnathopods 1 and 2, basis, anteriormarginbearingafringeof setaeorspines (Fig. 104) ......... J. hartmannae Conlan, 1990
- Gnathopods 1 and 2, basis, anterior margin without an obvious fringe of setae or spines (setae minute or restricted distally (Figs 37, 60 and 96) ..........................................................................................22
22 Gnathopod 2, female, palm sinuous (Fig. 97). Gnathopod 2, propodus of the major form thumbed male, thumb short with acute tip, spineorspinegroupontheposteriormarginattheoriginof thethumb onaledge (Fig. 96). Southern Hemisphere ......... .......................................................................... J. kjetilanna Vaderand Krapp, 2005
- Gnathopod 2, female, palm concave (Fig. 37). Gnathopod 2, propodus of the major form thumbed male, thumb long with rounded or incised tip, spine or spine group on the posterior margin at the origin of the thumb residual or absent (Figs 39 and 60). Northern Hemisphere ............................................................................................23
23 Antenna 2 markedly larger than antenna 1, width up to 2x the width of antenna 1 in the thumbed male. Gnathopod 2, propodus of themajorformthumbedmale, thumbtipnotincised (Fig. 60). North Pacific ............................... J. kimi n. sp.
- Antenna 2 not markedly larger than antenna 1, width up to 1.5x the width of antenna 1 in the thumbed male. Gnathopod 2, propodusof themajorformthumbedmale, thumbtipincised (Figs 37–39). North Atlantic.................. J. pusilla (Sars, 1894)
description: Published as part of Conlan, Kathleen E., Desiderato, Andrea & Beermann, Jan, 2021, Jassa (Crustacea: Amphipoda): a new morphological and molecular assessment of the genus, pp. 1-191 in Zootaxa 4939 (1) on pages 162-163, DOI: 10.11646/zootaxa.4939.1.1, http://zenodo.org/record/4580622