Paramarteilia canceri sp. n. (Cercozoa) in the European edible crab (Cancer pagurus) with a proposal for the revision of the order Paramyxida Chatton, 1911.

A new species, Paramarteilia canceri sp. n., is described using light and electron microscopy from the edible crab Cancer pagurus L. captured from the English Channel. No external symptoms were noted, although infected animals were typically lethargic and unresponsive to external stimuli. Organs of infected animals were shrunken and collapsed compared with apparently healthy individuals. Although the infection was systemic, marked host responses were only noted in the hepatopancreas where the parasite induced a pronounced haemocytic infiltration. Prevalence of infection throughout the study was 1.1%, with a maximum monthly prevalence of 3%. The intracellular parasite was typically 15 microm in length and composed of a primary cell containing up to three secondary cells derived by internal cleavage. Each secondary cell contains two bicellular spores. The parasite is readily differentiated from the other described paramyxean species by a combination of the number of secondary and tertiary cells. In light of this new discovery, a revision of the order Paramyxida Chatton, 1911 is proposed based upon comparison to the original descriptions of this parasite group in various species of invertebrate hosts. The proposed classification is based on the number of cells within the spores (tertiary cells), so that only three genera remain within the order, namely Marteilia Grizel, Comps, Bonami, Cousserans, Duthoit et Le Pennec, 1974, Paramarteilia Ginsburger-Vogel et Desportes, 1979 and Paramyxa Chatton, 1911. Subsequent discrimination of species is based on a combination of the number of secondary cells within the primary cell and the number of tertiary cells within secondary cells. It is proposed that the genus Marteilioides Comps, Park et Desportes, 1986 is suppressed and the type species of the genus, M. chungmuensis Comps, Park et Desportes, 1986, is transferred to Marteilia and that the other representative of the genus, M. branchialis Anderson et Lester, 1992, is transferred to Paramarteilia. Further, Paramyxoides Larsson et Køie, 2005 is considered as a junior synonym of Paramyxa and its type and only species, Paramyxoides nephtys Larsson et Køie, 2005, is transferred to Paramyxa.