Abstract
Abstract Morphology in general and developmental morphology in particular provide us with an insight into the evolution, phylogeny, ecological features, behavior, and life cycle of organisms. The present study describes the external morphology of the first three postembryonic developmental stages (Stage 13) of two prominent European crayfish species, the noble crayfish Astacus astacus (Linnaeus, 1758) and the narrowclawed crayfish Pontastacus leptodactylus (Eschscholtz, 1823). External morphology and setation of appendages are similar, presence of recurved tips for cheliped in Stage I and then the tip lost in Stage 2, long plumose setae on the telson in Stage 2 and then the setae disappearance in Stage 3 accompanied with the fully developed tail fan. The number of segments on antennal flagella differs between the species in Stage I and Stage II. Observed findings on early postembryonic development are consistent between European and North American (Pacifastacus sp.) astacid species, but differ in certain aspects from other crayfish families.
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