229 J. Parasitol., 91(1), 2005, pp. 229–231  American Society of Parasitologists 2005 An Ectosymbiotic Flatworm, Temnocephala chilensis, as Second Intermediate Host for Echinoparyphium megacirrus (Digenea: Echinostomatidae) in Patagonia (Argentina) G. Viozzi, V. Flores, and C. Rauque, Laboratorio de Parasitologı ´a, Universidad Nacional del Comahue, Quintral 1250, 8400 Bariloche, Rı ´o Negro, Argentina. e-mail: gviozzi@bariloche.com.ar FIGURE 1. Specimen of Temnocephala chilensis parasitized by meta- cercariae of Echinoparyphium megacirrus. Bar = 500 m. ABSTRACT: During a survey of parasites of the Patagonian freshwater crab Aegla neuquensis neuquensis, its ectosymbiont Temnocephala chi- lensis 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. me- gacirrus were obtained from domestic chicks experimentally infected with metacercariae obtained from temnocephalans. This is the first re- cord of temnocephalans being parasitized by digeneans. Temnocephalans are ectocommensal flatworms associated with a va- riety of freshwater crustaceans, insects, gastropods, and turtles from Australia and the Neotropical Region (Damborenea, 1998). In Patagon- ia, the freshwater decapod Aegla neuquensis neuquensis Schmitt ranges from 37°S to 46°S (Ringuelet, 1949), being a common host for Tem- nocephala chilensis (Moquin-Tandon, 1846) (Damborenea and Cannon, 2001). The life cycle of this flatworm is simple. The adult attaches eggs to the surface of a host and an immature worm hatches (Dioni, 1967). The life cycle of echinostomatids in the world includes snails as first intermediate hosts; gastropods, bivalves, fishes, tadpoles, and annelids as second intermediate hosts; and a wide range of birds, mammals, and reptiles as definitive hosts (Kanev et al., 2000). Some species of pla- narians have been experimentally infected with cercariae of Echinos- toma sp. Rudolphi, 1809 (Fried and Rosa-Brunet, 1991; Lo, 1995). In a review of the group, Kanev et al. (2000) did not indicate that meta- cercariae of Echinoparyphium sp. Dietz, 1909 were able to parasitize any species of platyhelminths. During a survey of parasites of A. n. neuquensis, the ectosymbiont T. chilensis was found to possess echinostomatid metacercariae. The aim of this study was to report the presence of metacercariae in T. chilensis, to identify the parasite species, and to determine its ability to infect avian hosts. Freshwater crabs were hand-collected from Andean Patagonian lakes and rivers in March 2003 (Table I). Specimens were transported live to the laboratory and examined for temnocephalans. Infected T. chilensis were then force-fed to 1-day-old domestic chicks: 15 metacercariae were given to one of them and 72 to another. The experimental hosts were killed 7 days after infection, following the procedure of Semenas et al. (1999). Adult flukes obtained were fixed in hot 5% formalin, stained with hydrochloric carmine, and mounted in Canada balsam. The metacercariae were found in the parenchyma of the body and in the tentacles of both immature and mature specimens of T. chilensis (Fig. 1). Eight ovigerous adults were obtained from 72 metacercariae given to 1 of the experimentally infected chicks. The morphometric characteristics of these specimens allowed us to identify them as Echin- oparyphium megacirrus (Semenas et al., 1999) (Table II). According to Buscher (1978), the following species of Echinopary- phium with 43 collar spines are considered valid: E. elegans (Looss, 1899); E. syrdariense Burdelev, 1937; E. bioccalerouxi, Dollfus, 1953; E. paracinctum Bychovskaya-Pavlovskaya, 1953; E. dunni Lie and Umathevy, 1965; and E. ralphaudyi Lie, Heyneman, Jayarasasingam, Mansour, Lee, Lee and Kostanian 1975. Mouahid and Mone ´ (1988) synonymized E. bioccalerouxi, E. ralphaudyi, and E. combesi Kech- emir, 1980 with E. elegans; subsequently, Kanev et al. (1994) synon- ymized E. cinctum (Rudolphi, 1803) with E. dunni. When comparing E. megacirrus and E. elegans (Mouahid and Mone ´, 1988), they were found to differ in the arrangement of collar spines (4-4-4-4 and 5-5-3- 3, respectively), in the length of corner spines (36–48 m and 42–55 m, respectively), and in the egg size (98–108 m and 75–91 m, respectively). In addition, E. megacirrus differs from E. cinctum and E. rubrum (Kanev et al., 1994, 1998) in the length of spines (40–90 m and 76–121 m, respectively) and in the length of eggs (90–120 m and 85–120 m, respectively). Of the 414 T. chilensis collected, 106 (26%) were parasitized with 189 (mean intensity = 1.8) metacercariae (Table III). The maximum prevalence of E. megacirrus in T. chilensis was detected in Lake Nahuel Huapi (29%) and the maximum mean intensity in Lake Ruca Choroi (2.3). Of the 41 crabs collected, 25 (61%) were parasitized by T. chi- lensis, and the highest prevalence was observed in the Alumine ´ River (100%). This is the first record of temnocephalans infected by digeneans and the first of a species of Echinoparyphium parasitizing any flatworm. Little is known about the life cycle of E. megacirrus in Patagonia. The natural definitive host of E. megacirrus is unknown, and the second intermediate host is the freshwater clam Diplodon chilensis (Gray) (Se- menas et al., 1999). Semenas et al. (1999) obtained ovigerous adults of E. megacirrus from experimentally infected 1-day-old domestic chicks but not from mice fed metacercariae.