GAMMERUS OR SCUD
(fast moving side swimmers, the scud indicates better water
quality than the previous species on the opposite page)
FIG. 1 - Structure of Amphipoda. A, male Pontoporeia affinis
(Lindstrom), x9; B, basal portion of first antenna of male P. affinis
; C, anterior end of female P. affinis; D, first antenna of female
Hylalella azteca (Saussure); E, third uropod of H. azteca. a2
, second abdominal segment; a6, sixth abdominal segment; cp,
coxal plate; p3, third pereiopod; pl, third pleopod;
t, telson; u1, first uropod. (A to C modified from
Segerstrale; D, redrawn from Geisler; E redrawn from Weckel, 1907.)
CRAYFISH
(another good indication of water quality)
FIG. 2 - Structure of a typical crayfish. a, acumen; ar,
areola; c, cervical groove; h, hand; mf,
movable finger of chela; p3, third leg (pereiopod); p5,
fifth leg (pereiopod); pr, postorbital ridge; r,
rostrum; t, telson; u, uropod (Modified from Hobbs, 1942a.)
Fig. from Pennak Robertt, Fresh - Water Invertebrates of the U.S.
