O gênero Okenia possui cerca de 50 espécies distribuídas ao redor do mundo, o qual claramente necessita de uma profunda revisão taxonômica. No Brasil, até então, são reportadas apenas três espécies: Okenia impexa, O. evelinae -- ambas com localidade-tipo em São Paulo -- e O. zoobotryon que foi originalmente descrita para Bermudas. Entretanto os registros de O. zoobotryon em águas brasileiras são ainda questionáveis. Esta espécie tem sido considerada durante muitos anos uma das mais problemáticas dentro do gênero, com outras como O. evelinae e O. polycerelloides já tendo sido propostas como sinônimas de O. zoobotryon e revalidadas por diferentes autores. Adicionalmente, O. zoobotryon tem sido reportada em diferentes partes do mundo, supostamente apresentando uma distribuição praticamente cosmopolita. Nesse contexto, este estudo apresenta uma análise morfológica e molecular de espécimes previamente identificados como O. zoobotryon procedentes de Bermudas, Austrália e Brasil. Além disso, exemplares de O. evelinae também foram analisados, com o intuito de esclarecer a possível sinonímia entre estas espécies. A análise morfológica revelou que os exemplares da Austrália são de fato uma espécie diferente, recentemente descrita como Okenia harastii, enquanto os espécimes do Brasil pertencem à espécie O. polycerelloides, que é claramente diferente de O. zoobotryon proveniente das Bermudas. Os principais caracteres anatômicos que corroboram a distinção entre as espécies aqui estudadas estão presentes na rádula e nos sistemas reprodutor e nervoso. A coloração é muito diferente entre O. evelinae e O. zoobotryon, porém a morfologia não as separou claramente, o que foi conseguido através de estudos moleculares preliminares. Dessa forma, ao contrário do que se pensava, O. zoobotryon parece estar restrita ao Oceano Atlântico Norte / The genus Okenia has about 50 species distributed around the world, which clearly need a deep taxonomic revision. In Brazil only three species are reported: Okenia impexa, O. evelinae -- both with type locality in São Paulo, Brazil -- and O. zoobotryon. Originally described from Bermuda, the records of the latter on the Brazilian waters are still questionable. In fact this species has been one of the most problematic in the genus. Okenia evelinae and O. polycerelloides have already been considered as synonyms of O. zoobotryon and were revalidated by different authors. Additionally, O. zoobotryon has been reported in different parts of the world, with a supposed cosmopolitan distribution. Thus, this study presents a morphological and molecular analysis of specimens previously identified as O. zoobotryon from Bermuda, Australia, and Brazil. We also studied specimens of O. evelinae in order to clarify the possible synonymy of these species. The morphological analysis revealed that the specimens from Australia are indeed a different species, recently described as Okenia harastii, while the ones from Brazil belong to Okenia polycerelloides, which is clearly distinct from O. zoobotryon. The distinctive anatomical characteristics that justify the separation among the species studied here are present in the radula, and reproductive and nervous systems. The color is very different between O. evelinae and O. zoobotryon, but the morphology did not clearly separate these two taxa. However, preliminary molecular data reveal that they are two distinct species. Thus, contrary to what was thought O. zoobotryon seems to be restricted to the North Atlantic Ocean.

In the Indian River Lagoon, the nudibranch Okenia zoobotryon and its egg masses are found attached to the bryozoan Zoobotryon verticillatum throughout the year. Okenia zoobotryon is thought to live, feed, and reproduce exclusively on Z. verticillatum, which would make this a very specialized predator-prey interaction. The primary goal of my study was to document certain aspects of the ecological and chemical relationships between Z. verticillatum and O. zoobotryon. Specifically, I wanted to understand the cues used by the nudibranch to locate and remain on Z. verticillatum. Population surveys on Z. verticillatum, as well as other potential hosts, were performed. From these surveys, I found a small number of O. zoobotryon adults and egg masses on the red macroalga S. filamentosa mixed with Z. verticillatum (0.01 and 0.05 g/wet-weight, respectively), none on the bryozoan Amathia distans, and none on the red macroalga Gracilaria tikvahiae. To determine if prey identification was associated with an adult cue, I ran paired-choice trials. In these, the adults did not significantly prefer Z. verticillatum. Next, laboratory culture of larvae of O. zoobotryon was performed. During larval culture some aspects of this previously undocumented life-history were recorded; adults of this species developed from planktotrophic veliger larvae that hatched out of egg masses between 4 and 6 days, the time post-hatching to settlement was 7-8 days, and metamorphosis occurred approximately 24 hours after settlement. The final question addressed in this study was; "Does O. zoobotryon feed on and take up chemicals from Z. verticillatum?" To address this question, high-performance liquid chromatography was performed on extracts of Z. verticillatum and O. zoobotryon. Both organisms were compared and found to contain similar compounds, which suggest that the nudibranch is feeding on Z. verticillatum and taking up chemicals. Concentrations of compounds in Z. verticillatum varied between populations in the northern and southern regions of the Indian River Lagoon. There are, also, differences between the chemical composition of Z. verticillatum in the IRL (northern and southern) and the California species identified by Sato and Fenical (1983).