Phoresis of the Green Hydra, Chlorohydra viridissima (Pall.), on a larval Anax imperator Leach under laboratory conditions (Hydrozoa: Hydrina; – Anisoptera; Aeshnidae)

Phoresis is a widespread phenomenon in nature. Phoretic associations of members of diverse invertebrate taxa on Odonata larvae have already been reported. C. DE LA ROSA & A. RAMIREZ (1995, Odonatologica 24: 219-224) give an overview of Diptera and Trichoptera, and H. BEUTLER (1991, Die Flussjungfer, Kinderbuchverlag, Berlin, p. 19) and J.K. TUCKER & J.B. CAMERER (1994, Odonatologica 23: 179-181) describe phoresy of Bivalvia on odonates. This note reports on the first association of a coelenterate with an odonate. When rearing Anax imperator larvae in aquaria for predation experiments, the aquaria became colonized by polyps of Chlorohydra viridissima. Most of the hydras settled on the vertical glass walls. A few individuals settled on two vertical wooden sticks in the centre of the aquarium (placed as a substrate for the dragonfly larvae). One hydra was found on the tergum of the fourth abdominal segment of a male Amir. The supposed mechanism of settlement of the hydra on the mobile Anax larva was by floating, facilitated by water currents, induced by the oxygen pump or by a kind of somersaulting typical of hydra (see R. BUCHSBAUM et al., 1987, Animals without backbones. Univ. Chicago Press, Chicago, pp, 102-103).