meromorph

Meromorph is a term used in biology to describe an organism that exhibits partial metamorphosis, in which the juvenile and adult stages share some morphological traits but differ in others; the transition between stages is incomplete, and the morphology is not a straightforward juvenile form that becomes a distinct adult form as in holomorphy. In meromorph development, certain adult features may be present in the juvenile form or may fail to fully develop until later, resulting in a mixed or intermediate morphology across life stages. The concept is used mainly in invertebrate zoology, particularly among crustaceans such as copepods, amphipods, and isopods, where life cycles can include larval forms that resemble adults in some respects while lacking reproductive maturity or specialized adult structures. Meromorphs are contrasted with holomorphs (complete metamorphosis into a distinct juvenile and adult form) and with anamorphs (stages that add new structures progressively after hatching).

Etymology: From Greek meros meaning part and morphe meaning form.

Notes: The term is relatively specialized, not widely used across all taxa, and definitions can vary by author. Some researchers prefer to describe the phenomenon in terms of heterochrony or paedomorphosis rather than as a separate metamorphosis category.