It is puzzling that one genus, Heterom esus, is represented by no less than An three different, hitherto undescribed species, of which five species were found exclusively in Thalassia rhizomes at four stations between 4417 and 8330 m, mainly in the Puerto Rico Trench (Fig. 6f ,g,h) No mention of Thalassia or other plant material has been made in conection with the altogether 34 records of the twelve previously known species of Fieteromesus, five of which are bathyal, two bathyal-abyssal, and five abyssal. Heteronesus belongs to the family Ischnomesidae another with other seven genera. Usually the long, fragile antennae and legs of the Ischnomesidae (and other similar deep-sea isopods) are lost in the trawl, but the rhizomes have preserved the Heteromesus species (and the other tiered iscpods) in a remarkable way.