title: Mikrocytids are a broadly distributed and divergent radiation of parasites in aquatic invertebrates.
abstract: Microcell parasites have independently evolved in several eukaryotic lineages and are increasingly recognized as important and emerging pathogens of diverse hosts, including species of economic importance subject to international legislation concerning the trading of aquatic animals [1-3]. The microcell Mikrocytos mackini causes Denman Island disease of oysters and represents one of the most genetically divergent eukaryotes known. Mikrocytos has remained an isolated lineage with a limited distribution. We investigated two emerging diseases of juvenile crabs and oysters from the UK using massively parallel sequencing and targeted primer approaches to reveal that their causative agents are highly divergent lineages related to M. mackini (Paramikrocytos canceri n. gen. et n. sp. and M. mimicus sp. nov., respectively). We demonstrate a major new globally distributed parasite radiation (Mikrocytida ord. nov.) with phylogenetic affinities to the commercially important haplosporidian parasites of invertebrates. Mikrocytids have eluded detection because of their small size, intracellular habit, and extreme sequence divergence. P. canceri was frequently detected in a range of shoreline invertebrates, demonstrating that these newly recognized parasites are in fact common, diverse, and widespread and should be considered when assessing the risks of aquaculture activities, invasive species spread, and movements of ballast water and sediments with associated invertebrates.
authors.affiliation: Department of Life Sciences, The Natural History Museum, Cromwell Road, London SW7 5BD, UK; EAWAG, Department of Aquatic Ecology and ETH-Zurich, Institute of Integrative Biology (IBZ), Überlandstrasse 133, 8600 Dübendorf, Switzerland.
authors.forename: Hanna
authors.initials: H
authors.lastname: Hartikainen
authors.affiliation: Centre for Environment, Fisheries, and Aquaculture Science (Cefas), Barrack Road, The Nothe, Weymouth, Dorset DT4 8UB, UK; European Union Reference Laboratory for Crustacean Diseases, Cefas, Barrack Road, The Nothe, Weymouth, Dorset DT4 8UB, UK. Electronic address: grant.stentiford@cefas.co.uk.
authors.forename: Grant D
authors.initials: GD
authors.lastname: Stentiford
authors.affiliation: Centre for Environment, Fisheries, and Aquaculture Science (Cefas), Barrack Road, The Nothe, Weymouth, Dorset DT4 8UB, UK; European Union Reference Laboratory for Crustacean Diseases, Cefas, Barrack Road, The Nothe, Weymouth, Dorset DT4 8UB, UK.
authors.forename: Kelly S
authors.initials: KS
authors.lastname: Bateman
authors.affiliation: Department of Life Sciences, The Natural History Museum, Cromwell Road, London SW7 5BD, UK.
authors.forename: Cédric
authors.initials: C
authors.lastname: Berney
authors.affiliation: Centre for Environment, Fisheries, and Aquaculture Science (Cefas), Barrack Road, The Nothe, Weymouth, Dorset DT4 8UB, UK.
authors.forename: Stephen W
authors.initials: SW
authors.lastname: Feist
authors.affiliation: Centre for Environment, Fisheries, and Aquaculture Science (Cefas), Barrack Road, The Nothe, Weymouth, Dorset DT4 8UB, UK.
authors.forename: Matt
authors.initials: M
authors.lastname: Longshaw
authors.affiliation: Department of Life Sciences, The Natural History Museum, Cromwell Road, London SW7 5BD, UK.
authors.forename: Beth
authors.initials: B
authors.lastname: Okamura
authors.affiliation: Centre for Environment, Fisheries, and Aquaculture Science (Cefas), Barrack Road, The Nothe, Weymouth, Dorset DT4 8UB, UK.
authors.forename: David
authors.initials: D
authors.lastname: Stone
authors.affiliation: Department of Life Sciences, The Natural History Museum, Cromwell Road, London SW7 5BD, UK.
authors.forename: Georgia
authors.initials: G
authors.lastname: Ward
authors.affiliation: Department of Life Sciences, The Natural History Museum, Cromwell Road, London SW7 5BD, UK.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Wood
authors.affiliation: Department of Life Sciences, The Natural History Museum, Cromwell Road, London SW7 5BD, UK.
authors.forename: David
authors.initials: D
authors.lastname: Bass
mesh_terms: D000818:Animals; D017756:Aquaculture; D003386:Brachyura / Q000469:parasitology*; D017125:Genes, Protozoan; D058865:Introduced Species; D008969:Molecular Sequence Data; D010125:Ostreidae / Q000469:parasitology*; D010802:Phylogeny; D056901:Rhizaria / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*; D006113:United Kingdom