Abstract
Larval stages of A. simplex (Rudolphi, 1809, det. Krabbe, 1878) and P. decipiens (Krabbe, 1878), infecting marine teleosts from New Zealand waters are described and compared morphometrically to pre‐adult and adult stages. A. simplex larvae were positively identified using adults obtained from in vitro cultivation. Some morphometric variations compared to overseas descriptions are noted; the main differences being the small size of A. simplex larvae and the long intestinal caecum in P. decipiens larvae and adults from New Zealand waters.