Ultrastructure, phylogeny and histopathology of two novel haplosporidians parasitising amphipods, and importance of crustaceans as hosts

ABSTRACT: This study provides morphological, ultrastructural and phylogenetic characterization
of 2 novel species of the order Haplosporida (Haplosporidium echinogammari n. sp. and H. orchestiae
n. sp.) infecting amphipods of the genera Echinogammarus and Orchestia collected in southwestern
England. Both parasites infect the connective tissues associated with the digestive gland and
the tegument, and eventually infect other organs causing disruption of host tissues with associated
motor impairment and fitness reduction. Prevalence of infection varied with host species, provenance
and season, being as high as 75% for individuals of E. marinus infected with H. echinogammari
in June (n = 50). Although no spores were found in any of the infected amphipods examined
(n = 82), the morphology of monokaryotic and dikaryotic unicellular stages of the parasites
enabled differentiation between the 2 new species. Phylogenetic analysis of the new species
based on the small subunit (SSU) rDNA gene placed H. echinogammari close to H. diporeiae in
haplosporidian lineage C, and H. orchestiae in a novel branch within Haplosporidium. An additional
25 new haplosporidian SSU rDNA sequences were generated from crab, isopod, and crayfish
samples, significantly increasing the number of crustacean-derived sequences within Haplosporida,
which was previously thought to comprise mostly parasites of molluscs. Phylogenetic
analysis of these new sequences revealed 3 clades of primarily crustacean-derived sequences within
Haplosporida.