Digenean parasites of deep-sea teleosts: a review and case studies of intrageneric phylogenies.

Studies on the digenean parasites of deep-sea (> 200 m depth) teleosts are reviewed and two case study generic phylogenies are presented based on LSU rDNA and ND1 mtDNA sequences. The phylogeny of the lepocreadiid genus Lepidapedon, the most common deep-sea digenean genus, is not clearly resolved as the two gene trees are not compatible. It can be inferred, however, that the genus has radiated in the deeper waters off the continental shelf, mainly in fishes of the gadiform family Macrouridae. Steringophorus, a fellodistomid genus, is better resolved. In this case a deep-sea radiation is also indicated, but the pattern of host-specificity is not clear, with evidence of much host-switching. Results of studies of the parasites of the macrourid fish Coryphaenoides (Nematonurus) armatus from various depths have reinforced recent views on the lack of zoned depth-related communities in the deep-sea. The diversity of deep-sea digeneans is relatively low with only 18 families (of about 60) reported. Little, or nothing, is known from most deep-sea areas and nothing from trenches and mid-ocean ridge systems.