appendages as larvae prior to the final molt and metamorphosis. Beetle larvae, for example, can regenerate amputated limbs. Fruit fly larvae do not have limbs but can regenerate their appendage primordia, imaginal discs. In both systems, the regrowth of the new tissue delays pupation. Mechanisms underlying appendage limb regeneration in insects and crustaceans are highly conserved. During limb regeneration species in both taxa form a blastema that proliferates and grows to repattern the missing tissue. Venom regeneration Arachnids, including scorpions, are known to regenerate their venom, although the content of the regenerated venom is different from the original venom during its regeneration, as the venom volume is replaced before the active proteins are all replenished. Fruit fly model The fruit fly Drosophila melanogaster is a useful model organism to understand the molecular mechanisms that control regeneration, especially gut and germline regeneration. In these tissues, resident stem cells continually renew lost cells. The Hippo signaling pathway was discovered in flies and was found to be required for midgut regeneration. Later, this conserved signaling pathway was also found to be essential for regeneration of many mammalian tissues, including heart, liver, skin, and lung, and intestine. Annelids Many annelids (segmented worms) are capable of regeneration. For example, Chaetopterus variopedatus and Branchiomma nigromaculata can regenerate both anterior and posterior body parts after latitudinal bisection. The relationship between somatic and germline stem cell regeneration has been studied at the molecular level in the annelid Capitella teleta. Leeches, however, appear incapable of segmental regeneration. Furthermore, their close relatives, the branchiobdellids, are also incapable of segmental regeneration. However, certain individuals, like the lumbriculids, can regenerate from only a few segments. Segmental regeneration in these animals is epimorphic and occurs through blastema formation. Segmental regeneration has been gained and lost during annelid evolution, as seen in oligochaetes, where head regeneration has been lost three separate times. Along with epimorphosis, some polychaetes like Sabella pavonina experience morphallactic regeneration. Morphallaxis involves the de-differentiation, transformation, and re-differentation of cells to regenerate tissues. How prominent morphallactic regeneration is in oligochaetes is currently not well understood. Although relatively under-reported, it is possible that morphallaxis is a common mode of inter-segment regeneration in annelids. Following regeneration in L. variegatus, past posterior segments sometimes become anterior in the new body orientation, consistent with morphallaxis. Following amputation, most annelids are capable of sealing their body via rapid muscular contraction. Constriction of body muscle can lead to