Crustacean larva stop after a single copepodid stage. Once the gonads develop, there are no further moults. Chalimus (plural chalimi) is a stage of development of a copepod parasite of fish, such as the salmon louse ("Lepeophtheirus salmonis"). "Chalimus" Burmeister, 1834 is also a synonym for "Lepeophtheirus" Nordmann, 1832. The single genus in the Facetotecta, "Hansenocaris", is only known from its larvae. They were first described by Christian Andreas Victor Hensen in 1887, and named "y-nauplia" by Hans Jacob Hansen, assuming them to be the larvae of barnacles. The adults are presumed to be parasites of other animals. Crustacean larva Crustaceans may
Genus of a quadratic form the same genus have equal discriminant and hence there are only finitely many equivalence classes in a genus. The Smith–Minkowski–Siegel mass formula gives the "weight" or "mass" of the quadratic forms in a genus, the count of equivalence classes weighted by the reciprocals of the orders of their automorphism groups. For binary quadratic forms there is a group structure on the set "C" equivalence classes of forms with given discriminant. The genera are defined by the "generic characters". The principal genus, the genus containing the principal form, is precisely the subgroup "C" and the genera are the cosets of "C":