Mysidopsis, G. O. Sars, 1864

Price, W. Wayne, 2024, Mysidopsis jenseni n. sp. from the Pacific coast of Washington, with first description of female M. intii Holmquist, 1957 (Crustacea: Mysida: Mysidae), Zootaxa 5399 (4), pp. 397-417 : 414-415

Key to the species of Mysidopsis from Pacific coasts of the Americas

1 Uropodal endopod with 16 or more spiniform setae or spines along ventro-medial margin distal to statocyst............. 2

- Uropodal endopod with fewer than 16 spiniform setae along ventro-medial margin distal to statocyst................... 5

2 Antennal scale apex acutely pointed...................................................................... 3

- Antennal scale apex rounded............................................................................ 4

3 Antennal scale 7.0–10 times as long as maximum width; carapace, anterior margin produced into a short, bluntly rounded subtriangular rostrum, not covering any part of eyestalks; thoracic endopods 3–8 with 2-articulate carpopropodus; telson apex, median pair of spiniform setae equal to or slightly longer than adjacent pair.......................................................... M. californica W. Tattersall, 1932 ( USA: California; Mexico: Baja California, Sinaola; shallow water)

- Antennal scale about 5 times as long as maximum width; anterior margin produced into a subtriangular rostrum, extending about half the length of eyestalks; thoracic endopods 3–8 with 3-articulate carpopropodus; telson apex, median pair of spiniform setae at least 2 times longer than adjacent pair........................................................................... M. acuta Hansen, 1913 ( Chile, Tierra del Fuego, Patagonian Shelf, Falkland Islands, South Georgia; 0–250 m)

4 Uropodal endopod with 30–43 short spines in 8–10 groups of 2–7 spines each along a straight or slightly undulating ventro-medial margin from the region of the statocyst to the apex; thoracic endopods 3–8 with 2-articulate carpopropodus; telson apex densely armed with 5–6 subequal spiniform setae............................................................................................ M. intii Holmquist, 1957 ( Chile: Los Lagos, Coquimbo: USA: California; 1.0–6.0 m)

- Uropodal endopod with 16–20 fairly large spiniform setae along ventro-medial margin from the statocyst to the apex; thoracic endopods 3–8 with 3-articulate carpopropodus; sexual dimorphism exhibited; female telson apex with 2 pairs of long, stout spiniform setae, about 0.3 length of telson; male telson apex with 3 pairs of fairly stout spiniform setae, inner-most pair about 0.2 length of telson............ M. gemina Price, Heard and Vargas, 2019 ( Costa Rica: Puntarenas, Guanacaste; 0.5–1.0 m)

5 Telson , total number of spiniform setae about 80; telson length (excluding apical setae) about 2.2 times maximum basal width; uropodal endopod with 12 spiniform setae along ventro-medial margin from region of statocyst distally; antennal scale with no distal suture, about 9 times as long as maximum width............. M. cathengelae Gleye, 1982 ( USA: California; 7–8 m)

- Telson, total number of spiniform setae 30–60; telson length (excluding apical setae) 1.4–1.5 times maximum basal width; uropodal endopod with 5–9 spiniform setae from region of statocyst distally; antennal scale with distal suture, 3.0–4.5 times as long as maximum width................................................................................ 6

6 Telson , total number of spiniform setae about 30, inner-most pair of apical spiniform setae 2 times as long as adjacent pair.................................................. M. brattegarti Băcescu and Gleye, 1979 ( USA: California; 12 m)

- Telson, total number of spiniform setae 40–60, inner-most pair of apical spiniform setae less than 2 times as long as adjacent pair................................................................................................ 7

7 Uropodal endopod with 5 spiniform setae along ventro-medial margin from region of statocyst distally; carapace, anterior margin produced into a strong subtriangular rostrum with acute apex; female carapace lacking lappet near midline of posterior margin......................................... M. onofrensis Băcescu and Gleye, 1979 ( USA: California; 15–75 m)

- Uropodal endopod with 8–9 spiniform setae along ventro-medial margin from region of statocyst distally; anterior margin produced into a strong subtriangular rostrum with rounded apex; female carapace with ovoid to trilobed lappet near midline of posterior margin.................................................. M. jenseni n. sp. ( USA: Washington; 8–15 m)