The study of twenty-nine oligochaete samples collected in 1996 by J. H. Stock and J. J. Vermeulen (University of Amsterdam), in the Sultanate of Oman, allowed us to draw up an initial inventory of the freshwater oligochaete fauna of the Arabian peninsula, a fauna totally unknown until now. The 147 specimens examined belong to nine species of four families: Phreodrilidae, Naididae, Tubificidae and Enchytraeidae. The Phreodrilidae (2 species) represent more than half of the total specimens; whilst the rest belong mainly to the Naididae.
Two new species of Phreodrilidae (Antarctodrilus arabicus n. sp. and Phreodrilus stocki n. sp.) are described. Both belong to the subfamily Phreodrilinae, until now not reported from north of the tropic of Capricorn. Other identified species include Dero (Dero) zeylanica, Allonais paraguayensis and Doliodrilus puertoricensis, which are for the first time recorded in subterranean habitats.
These studies confirm the hypothesis of the presence of Phreodrilidae in the Arabian peninsula as relict taxa inhabiting refuges in hyporheic/groundwater habitats.
The presence of an oligochaete fauna with marine phyletic affinities in underground waters already highlighted in Europe now equally applies to the Arabian peninsula with the discovery of the tubificid genera Aktedrilus and Doliodrilus in the underground habitats of Oman. As these genera already are well known from the littoral marine or brackish water with a wide range of salinity, we have additional evidence that the migration of interstitial marine meiobenthic tubificid species through water of decreasing salinity may be a way of colonising the subterranean freshwaters.
The present record of Doliodrilus puertoricensis (Limnodriloidinae), previously known from Puerto Rico and Belize in the western Atlantic Ocean, represents a large extension of its known distribution area.