The tantulocarid life cycle is unique among crustaceans. The tantulus larva transforms directly from a non-feeding (lecithotrophic) and free-swimming organism into a parasite without any
instars. When entering the parasitic stage much of the body, such as the muscles, degenerates, even if the body itself becomes bigger. As a parasite it is permanently attached to its host, and after piercing its host's cuticle with an unpaired stylet, a rootlet system used to absorb nutrients enters through the hole and grow into the host's tissue. The adult form develops inside the larva, and can become either a sac-like
parthenogenetic female, or a fully developed free-living, non-feeding and sexually-reproducing male or female. The eggs inside the parthenogenetic female are eventually released as fully developed tantulus larvae. The finding of what appears to be a benthic non-feeding
nauplius larva suggests that eggs produced by sexual females hatch as nauplii instead of tantulus larvae. Both the parthenogenetic and sexual females are
semelparous. ==Classification==