CLASS MAXILLOPODA: SUBCLASS COPEPODA: Order Harpacticoida

1. Brief definition of the group and main diagnosing characters The Harpacticoida is one of the orders of the subclass Copepoda, and includes mainly free-living epibenthic aquatic organisms, although many species have successfully exploited other habitats, including semi-terrestial habitats and have established symbiotic relationships with other metazoans. Harpacticoids have a size range between 0.2 and 2.5 mm and have a podoplean morphology. This morphology is char-acterized by a body formed by several articulated segments, metameres or somites that form two separate regions; the anterior prosome and the posterior urosome. The division between the urosome and prosome may be present as a constriction in the more cylindric shaped harpacticoid families (e.g. Ectinosomatidae) or may be very pronounced in other familes (e.g. Tisbidae). The adults retain the central eye of the larval stages, with the exception of some underground species that lack visual organs. The harpacticoids have shorter first antennae, and relatively wider urosome than the copepods from other orders. The basic body plan of harpacticoids is more adapted to life in the benthic environment than in the pelagic environment i.e. they are more vermiform in shape than other copepods. Harpacticoida is a very diverse group of copepods both in terms of morphological diversity and in the species-richness of some of the families. Harpacticoids are extremely abundant yet, as a result of thei