Instar-specific head and body lengths of Hyalella(Amphipoda): criteria for starting and endpoints in experimental studies

Abstract Instar-specific data on head length and body length of Hyalella azteca was obtained from live specimens reared individually at 23 ± 1 °C under a 14L:10D photoperiod and with food ad lib. Both head length and body length were strong predictors of instar number through instars 1 – 10. The relationship between instar number and head length was linear (head length m] = 104.28 + 61.05instar]; r ²=0.98, P<0.001), whereas that between instar and body length was not (body length m] = 1339.28 + 55.82instar]²; r ² = 0.97 , P< 0.001). Head length measurements were easier to obtain and were more accurate than body measurements. Both measurements can be obtained without injury to the animal, permitting repeated observations on the same individual.