a condition in which males and females of the same species are morphologically different, usually indicated in unionoids by an expanded posterior marsupial area in the female in contrast to a more pointed or bluntly rounded area in the male. (Parmalee and Bogan 1998)

A marked difference in size and appearance between males and females of a species.

Refers to species that have noticeable physical differences between males and females (e.g. Heteropteryx dilatata, Extatosoma tiaratum).

species where the male and female are visibly different in appearance

a biological term used to describe external differences between males and females of the same species. For example, many bird species are sexually dimorphic with the males being bigger and more colorful than the females. Relative to harbor seals, there are no obvious external differences between males and females and, thus, they are not sexually dimorphic. Sexual dimorphism is evident in California sea lions with the males being much larger and having a bulging forehead.