Dawn of astome ciliates in light of morphology and time-calibrated phylogeny of Haptophrya planariarum, an obligate endosymbiont of freshwater turbellarians.

Morphology, systematic position and time-calibrated phylogeny of Haptophrya planariarum were investigated. This endosymbiont of freshwater turbellarians is characterized by: (i) a length of about 200-900 µm; (ii) a campanulate to truncate claviform body carrying an anterior adhesive sucker; (iii) an ellipsoidal macronucleus localized in the rear body end; (iv) a contractile canal extending along the dorsal margin; and (v) usually more than 150 meridional ciliary rows, a horseshoe-shaped suture line along the sucker, and two inconspicuous secant systems at lateral ends of the suture line. In 18S rRNA gene phylogenies, astomes were depicted as a non-monophyletic group within the scuticociliate clade, whereby H. planariarum clustered with the loxocephalid genus Dexiotricha. After considering morphological evidence, statistical tree topology tests and evolutionary distances, we find astomes as a distinct group that evolved from a free-living scuticociliate ancestor in the early Paleozoic. Molecular clock analyses indicated that astomes living in annelids diverged from those inhabiting turbellarians within about 50 Ma during the Late Cambrian and the Upper Ordovician. This comparatively short time span might have not sufficed for fixation of molecular synapomorphies in the 18S rRNA gene and/or they might have been erased by substitutions during the almost 500 Ma-long evolutionary history of astomes.

Urosporidium sp. hyperparasite of the turbellarian Paravortex cardii in the cockle Cerastoderma edule.

Cysts with spores showing different degree of maturity and a single plasmodium were observed in the connective tissue of the turbellarian Paravortex cardii located in the digestive lumen of the cockle Cerastoderma edule. The study of spore morphology by transmission electron microscopy revealed that they correspond to an haplosporidian belonging to the genus Urosporidium. Spore ornaments were similar to those described from Urosporidium spisuli, infecting a nematode parasite of the Atlantic surf clam, Spisula solidissima.

An ectosymbiotic flatworm, Temnocephala chilensis, as second intermediate host for Echinoparyphium megacirrus (Digenea: Echinostomatidae) in Patagonia (Argentina).

During a survey of parasites of the Patagonian freshwater crab Aegla neuquensis neuquensis, its ectosymbiont Temnocephala chilensis was found parasitized with an echinostomatid metacercaria with 43 collar spines. Of the 414 T. chilensis collected, 106 were parasitized with metacercariae of Echinoparyphium sp. Ovigerous adults of E. megacirrus were obtained from domestic chicks experimentally infected with metacercariae obtained from temnocephalans. This is the first record of temnocephalans being parasitized by digeneans.