 As with many crustaceans, larval development is metamorphic with immature forms differing greatly from those of adults.Embryos are carried in paired or single sacs attached to first abdominal somite (as seen in the illustration of the female "Sapphirina darwinii" above right).Most poecilostomatoid copepods are ectoparasites of saltwater fish or invertebrates (including among the latter mollusks and echinoderms).