Systematic Parasitology 37: 195–205, 1997. 195 c 1997 Kluwer Academic Publishers. Printed in the Netherlands. A new species of Lernaea L. (Copepoda: Cyclopoida) from Brazil, with notes on its ontogeny G.A. Boxshall 1 , M.A. Mont ´ u 2 and A. Schwarzbold 3 1 Department of Zoology, The Natural History Museum, London SW7 5BD, UK 2 Departmento de Oceanografia, Foundation University of Rio Grande, Cx. Postal 474, Rio Grande, CEP 96.201-900, RS, Brazil 3 Departamento de Ecologia, Instituto de Biociencias, Av. Paulo de Gama s/n., CEP 90.040-060 Porto Alegre, RS, Brazil Accepted for publication 3rd February, 1997 Abstract A new species of Lernaea, closely related to L. cyprinacea, is described from both native and introduced fish species at a fish farming facility in Rio Grande do Sul, Brazil. All life-cycle stages of the new species, L. devastatrix, can be distinguished from L. cyprinacea by the reflexed claw on its antenna. A partial scheme of homologies of the antennulary segments is proposed, and the development of the segmentation and setation patterns is traced from CoIII to adults of both sexes. New interpretations are proposed of the homology of the antennary claw and of the maxillipedal endopod in lernaeids. Introduction Thatcher (1991) included only two members of the family Lernaeidae Wilson, 1917 in his checklist of parasitic copepods from Neotropical freshwater fishes and Kabata (1979) listed only two species of Lernaea L. from the whole of South America, but in late 1995 a serious outbreak of lernaeosis occurred at an aqua- culture facility on the Rio Jacui near Porto Alegre in southern Brazil. Heavy infection was reported both on native Brazilian fishes (Hoplias malabaricus and Astyanax sp.) and on fish species (Cyprinus carpio var. specularis and Rhamdia aff. sapo) originally imported from abroad but bred for some generations in Brazil. Postmetamorphic and premetamorphic adult females, males and late copepodid stages were examined in an attempt to identify the parasite, which closely resem- bled the widely distributed Lernaea cyprinacea L. Materials and methods Adult lernaeids were removed from fish hosts taken from a fish farming facility on the Rio Jacui near Porto Alegre, Rio Grande do Sul, Brazil. Adult Ler- naea females were found infecting Hoplias malabar- icus, Astyanax sp., Cyprinus carpio var. specularis and Rhamdia aff. sapo and were dissected from their hosts. Fish infected with ovigerous female Lernaea were transported alive to the laboratories of the Foun- dation University of Rio Grande, Rio Grande but lat- er died. The dead fish were fixed in 10% formalin and the aquarium water was filtered through a fine mesh sieve. The mesh retained numerous copepodid stages and premetamorphic adults of Lernaea. The copepods were examined whole and with appendages dissected as temporary preparations in lactophenol on a Leitz Diaplan microscope using differential inter- ference contrast microscopy. All drawings were made with the aid of a camera lucida. Comparative material of Lernaea cyprinacea L. from the collections of The Natural History Museum was examined in order to check details of appendage structure. The material comprised numerous adult females of L. cyprinacea, collected from “goldfish” from a pond in Surrey UK, identified and presented by G. Fryer: BM(NH) Registration Numbers 1967.11.2.1.