Mesamphisopus, : Nicholls, 1943

Gouws, Gavin, 2008, New species of Mesamphisopus, an endemic South African freshwater isopod genus (Isopoda: Phreatoicidea: Mesamphisopidae), Zootaxa 1690, pp. 1-62 : 59-60

Key to the known species of Mesamphisopus

1 Antennal basal articles sparsely to moderately setose ............................................................................... 2

– Antennal basal articles heavily setose ....................................................................................................... 3

2 Pleotelson dorsal margin straight, apex continuous with and at same level as anterior dorsal margin (ventral inflection absent or very shallow), apex long and not up-turned .................................... M. paludosus

– Pleotelson dorsal margin gradually curving downwards with deep ventral inflection, apex below level of anterior dorsal margin, apex long and up-turned or very short ........................................... M. penicillatus

3 Uropodal protopod dorsomesial margin/ridge produced to some extent and plate-like ............................ 4

– Uropodal protopod dorsomesial margin approximately linear, not produced ........................ M. tsitsikamma

4 Pleotelson with subapical pair of dorsal robust setae ................................................................................ 5

– Pleotelson without subapical pair of dorsal robust setae ........................................................................... 6

5 Cephalon and pereon sparsely to moderately setose; antennula with 5 or 6 articles; pleotelson abrupt, stubby, dorsal margin sloping steeply with shallow ventral inflection, apex indefinite and hardly upturned; elongate setae abundant on uropodal rami ............................................................. M. abbreviatus

– Cephalon and pereon with abundant elongate setae, particularly laterally; antennula with 7 or 8 articles; pleotelson dorsal margin sloping gradually, ventral inflection deep, apex broad, small and up-turned; elongate setae sparse on uropodal rami or absent .......................................................................... M. depressus

6 Eyes small, diameter less than half the width of proximal antennal article and <0.10 head depth; body lacking pigmentation ................................................................................................................. M. albidus

– Eyes larger, diameter approximately half width of proximal antennal article and> 0.10 head depth; body pigmented or weakly pigmented ................................................................................................................ 7

7 Antennula short (<0.15 body length); antenna long (> 0.60 body length); pereopod I with distoventral cuticular process on propodal palm;> 10 robust setae on each of uropodal rami; body weakly pigmented ..................................................................................................................................................... M. setosus

– Antennula long (> 0.15 body length); antenna short (<0.60 body length); pereopod I without distoventral cuticular process on propodal palm; <6 robust setae on each of uropodal rami; body strongly pigmented .................................................................................................................................................................... 8

8 Pereopod I dactylus distoventral row of scale-like spines absent or weakly developed; pleotelson lateral uropodal ridge absent/weakly developed; abundant elongate setae on uropodal protopod and rami .......... ................................................................................................................................................... M. kensleyi

– Pereopod I dactylus distoventral row of scale-like spines well developed; pleotelson lateral uropodal ridge well developed; elongate setae on uropodal protopod and rami sparse to common ................................. 9

9 Antennular and antennal articles short, broad, inflated and bulbous; setae common to abundant on pereon and pleon .................................................................................................................................. M. baccatus

– Antennular and antennal articles long, slender, broadly rectangular; pereon and pleon sparsely setose ..... .................................................................................................................................................. M. capensis