<p>Life form (LF) is commonly defined as a group of species that share a common set of biological and morphological properties and are similar in general habitus and adaptations to a particular environment. For marine harpacticoids, several LFs have been distinguished based on their morphology, i.e., planktonic, phytal, epibenthic, burrowing and interstitial. We reviewed available data focused on LF ecology and demonstrated that each LF exhibited a consistently distinct set of properties. In particular, epibenthic species are predominant in fine silty sediments, burrowers and interstitial ones—in medium to coarse sands, while phytal species expectedly prefer macroalgal or sea grass habitats. Phytal and epibenthic harpacticoids can actively migrate into the water column, quickly disperse with currents and colonize new habitats, whereas interstitial species have the lowest dispersal ability. With respect to biogeographic distribution, planktonic species are most widespread, followed by phytal and then epibenthic forms, whereas burrowing and interstitial species generally have a restricted distribution. In addition, the LFs respond rather differently to different types of disturbances. These findings suggest that the classification of harpacticoids by LFs, even though not clear-cut and often provisional, is ecologically meaningful and has the potential for identifying patterns in community structure.</p>