The settlement pattern of epizoic organisms on the edible crab species such as Scylla serrata (Forskal), **Scylla tranquebarica (Fabricius) and Portunus pelagicus (Linnaeus) of the Pulicat Lake was surveyed. Ten species, three varieties and a form of epizoa infested the external parts of the 10% of host crabs of S. tranquebarica and their relative incidence to the size and site and to the different regions of this brackishwater lake was studied. The external epizoites settled mostly on the easily accessible carapace of larger crabs distributed mainly around the mouth of the lake. Encrustation both on S. serrata (0.3 %) and on P. pelagicus (0.2%) was strikingly insignificant.

The different gill-infesting pedunculate cirripeds were also examined as to their preferred gills and gill regions of S. tranquebarica, S. serrata and P. pelagicus. In the gill chamber the cirriped species infested largely the middle and the ventral regions of the middle gills which provided sufficient space as well as they are directly exposed to the inhalent resoiratory current of the host supplying food and oxygen to the epizoites.

Interestingly enough, no parasitic infestation was noticed on any of these crab species of the Pulicat Lake.