AbstractEfforts have begun to establish test subjects other than the intact pregnant mammal to serve as models for rapid teratology screens.Artemianauplii transcending instar I to later instars were examined to determine their potential for indicating chemicals as potential developmental hazards and thus prioritizing them for more extensive in vivo testing. Several criteria selected for assessing the system's potential for screening were the ability to: 1) collect homogeneous populations of instar I nauplii; 2) characterize intermediate development by technically simple measurements; and 3) demonstrate development‐related differentials in naupliar vulnerability.Homogeneous populations of nauplii were harvested from a flow‐through hatching and cold storage system. Nauplii accumulated in the system are stored at 4°C in a quiescent state with little physical (body length, body water volume) and biochemical (DNA and protein levels) change and thus are maintained at instar I. Intermediate development of nauplii transcending instar I to IV was characterized after the onset of 25°C incubation by measuring changes in drinking activity, body length, body water volume, and DNA and protein levels. During the first day of incubation, development was greatest between 6 and 24 hours of incubation.Development‐related differentials in naupliar vulnerability were shown by comparing median lethal concentrations (LC50) estimated for cadmium sulfate (CdSO4), mercuric chloride (HgCl2), and sodium azide (NaN3) at various times during incubation. With cadmium and mercury, LC50s decreased as nauplii aged and developed; whereas, with azide, LC50s did not vary. Developing nauplii were differentially vulnerable to cadmium and inorganic mercury.Artemianauplii transcending instar I to IV appear useful for indicating chemicals that preferentially interact with developmental