First record of endoparasitism of Pycnogonida in Hydrozoan polyps (Cnidaria) from the Brazilian coast

Abstract

Despite the relatively high number of recent studies on Cnidaria off the Brazilian coast, we have observed only two records of parasitism on macromedusae and none on polyps. Endoparasitic associations between Pycnogonida larvae and hydroids have been well known since the early 20th century. Protonymph larvae develop inside the gastrovascular cavity of polyps, typically gastrozooids, which are then called gallzooids. This short communication is an unprecedented record of parasitism on the polyps of Brazilian cnidarian fauna. The parasitic association between Pycnogonida Anoplodactylus stictus and a new hydroid species of Podocoryna has been casually detected on the encrusting communities of experimental polyethylene plates installed at the Paranaguá Yacht Club, Paranaguá, south of Brazil from February 2007 to February 2008. This hydrozoan host is most likely an exotic species because it had not been observed in previous studies of Paranaguá Bay or beaches along the southern coast of Brazil in the previous 20 years. Eighty-eight hydroid colonies were analyzed, of which 19 were parasitized mainly from June to August 2007. Protonymphs were pink-red colored, similar to gallzooids and all other polyps of the colony, thus indicating that they had eaten the hosts' tissues. Up to six protonymphs were observed inside the gallzooids. The gallzooid column was elongated, and the tentacles were atrophied or even absent because of the development of the larvae. Some observations of endoparasitism in two live colonies that were maintained in aquaria until their complete disappearance (one month) are also described in this note.