Paula Henttonen

A comparison of the known life forms of Psorospermium spp. in freshwater crayfish (Arthropoda, decapoda) with emphasis on Astacus astacus L. (Astacidae) and Procambarus clarkii (Girard) (Cambaridae)

Abstract Psorospermium spp. are unicellular organisms of uncertain taxonomic status found in the tissues of crayfish from three crayfish families. We describe the various life forms that we have identified in astacid, cambarid, and parastacid crayfish. A small amoeboid form, 10 μm, is described from juvenile North American Procambarus clarkii . A similar form had been described only once before in European Astacus astacus in the 1930s. Psorospermium spp. described to date are apparently otherwise immobile and often surrounded by a thick wall. Infection becomes apparent in 5th or 6th stage crayfish.

Occurrence of Psorospermium sp. in several North American crayfish species, with comparative notes on Psorospermium haeckeli in the European crayfish, Astacus astacus.

Abstract Psorospermium haeckeli is a thick-walled, unicellular organism widely reported in European astacid crayfish. Its taxonomic status and life cycle have not been elucidated. It is often referred to as a “parasite”, but conclusive evidence has yet to be found. Recent examination of two North American crayfish species, Procambarus clarkii and Procambarus zonangulus, confirmed its presence in the south-central USA (Louisiana) with morphologies that differ from that of P. haeckeli. This form had been previously reported from Orconectes virilis in southern Canada. We report here the presence of this North American form of Psorospermium in additional North American crayfish including Orconectes immunis and Orconectes rusticus from the northern USA (Minnesota and Wisconsin), Procambarus alleni and Procambarus fallax from the southern USA (Florida), and Pacifastacus leniusculus from the western USA. We also confirm this Psorospermium in O. rusticus from eastern Canada (Ontario). It was not, however, confirmed in several additional southern crayfish species including Cambarus diogenes, Cambarellus puer, Fallicambarus fodiens, and Orconectes palmeri. We describe the morphological forms of this Psorospermium and conclude that it is present in many crayfish species in North America.

The crayfish pathogen Psorospermium haeckeli activates the prophenoloxidase activating system of freshwater crayfish in vitro

Abstract Preparations of the crayfish pathogen Psorospermium haeckeli were found to activate the prophenoloxidase activating (proPO) system in haemocyte lysates of two crayfish species Pacifastacus leniusculus and Astacus astacus . This is the first report showing that this parasite can elicit the activation of a defence system in crayfish and that the activation appears to be similar to the activation of the proPO system triggered by different microbial polysaccharides.