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Sexual dimorphism has long been stressed as a remarkable characteristic of Eulimidae snails. This idea is so common for this family that, even without information on the soft parts, some species were already identified as male or female, as observed in Nanobalcis worsfoldi Warén, 1990. Here, we investigated whether larger and smaller individuals of N. worsfoldi are female and male, respectively, and what are the most useful characteristics to differentiate the sexes. We analyzed shell morphology and morphometry, along with coloration of the soft parts of large and small individuals, and crosschecked our findings through histological analysis. Our results confirmed that (i) larger and smaller individuals are females and males, respectively; (ii) shell morphology is not useful, while morphometry is important to address sexual dimorphism; (iii) since shell length and width showed the most remarkable differences, they are considered the best parameters to predict the sex. Furthermore, conchological characteristics associated with histological analysis suggest that this species could be the first non-sessile eulimid known as a sequential hermaphrodite (protandric) with environmental sex determination, but this remains to be confirmed. Considering that most studies on eulimids are based on shells, the morphometric parameters used here may support future ecological/biological analyses in the family, such as parasitological prevalence, or parasitic burden related to sex.

Sea slugs are interesting models to study post-copulatory sexual selection in simultaneous hermaphrodites due to the enormous variation of their reproductive systems. However, the knowledge of the functional morphology of their reproductive system is limited to few species, and it is rarely discussed in the context of sexual selection theory. In this study, we investigated the functional morphology of the sperm-containing chambers (i.e., ampulla, seminal receptacle, and bursa copulatrix) of the reproductive system of Okenia polycerelloides (Ortea & Bouchet, 1983), based on light, confocal, and electron microscopy. Although the morphology of the ampulla is similar to other species, indicating that it is a site for autosperm storage, we found some sperm facing the ampullar epithelium, a feature commonly regarded as characteristic of the seminal receptacle of sea slugs. The seminal receptacle of O. polycerelloides showed secretory activity and contained sperm with distribution and orientation suggestive of stratification of allosperm from distinct mating events, a feature that would affect sperm competition. The bursa copulatrix had epithelial cells with secretory and absorptive characteristics, and contained degraded sperm and yolk granules within its lumen. Comparative analyses of the contents of each organ demonstrated that sperm digestion occurs in the bursa copulatrix and affects sperm heads first, changing their morphology from slender and curved to shorter and ellipsoid before complete lysis. Although digestion and absorption of surplus sperm are currently the main hypothesized functions for the bursa copulatrix, its role in cryptic female choice should not be ruled out. The close structural connection between the seminal receptacle and bursa copulatrix, as well as their muscular walls, would enable control over the fate of the sperm received in each mating event, that is, storage or digestion.

A seleção sexual atua significativamente na diversificação de atributos reprodutivos. Muitos hermafroditas possuem órgãos para armazenamento e digestão de espermatozoides, os quais estão potencialmente envolvidos em mecanismos pós-copulatórios de seleção sexual, como competição espermática e escolha críptica da \"fêmea\". Tais processos geralmente ocorrem no interior do sistema reprodutor feminino, portanto, o conhecimento sobre sua morfologia funcional é de extrema importância para compreensão de mecanismos pós-copulatórios. Lesmas marinhas são predominantemente hermafroditas e possuem sistema reprodutor complexo, incluindo órgãos para armazenamento e digestão de esperma. Nesse contexto, o presente estudo teve como objetivo investigar o comportamento de cópula e a morfologia funcional dos órgãos que contêm esperma no sistema reprodutor feminino do nudibrânquio Okenia polycerelloides (Ortea & Bouchet 1983), bem como o comportamento de cópula do nudibrânquio Phydiana lynceus Bergh 1867. Para o estudo morfológico, foram empregadas técnicas de microscopia óptica, confocal e eletrônica. Manipulações experimentais e análises histológicas foram combinadas para investigar o destino dos espermatozoides dentro do sistema reprodutor após uma e duas cópulas subsequentes, e se a ausência de alimento influencia a ocorrência de digestão de espermatozoides. Os resultados sugerem função de recepção e armazenamento de espermatozoides para o receptáculo seminal, e de digestão de espermatozoides para a bursa copulatória. Cópulas múltiplas podem levar à estratificação de espermatozoides no receptáculo seminal. Embora a ausência de alimento aparente intensificar a digestão de esperma, ela não determinou sua ocorrência. A digestão de espermatozoides ocorreu continuamente, e pelo menos parte dos espermatozoides recebidos em cada cópula foi direcionada para a bursa copulatória, corroborando a hipótese prévia de digestão de espermatozoides supérfluos. Entretanto, todo o aloesperma recebido pode também ser digerido, sugerindo a possibilidade de escolha críptica. Redução gradual dos conteúdos da bursa copulatória associada ao aumento do tempo pós-cópula sugere reabsorção do material digerido. Interações de cópula em O. polycerelloides incluem contato mútuo utilizando a região oral, alinhamento corporal, intromissão do pênis e transferência de esperma. Porém, as interações podem ser interrompidas em qualquer um desses estágios, e mesmo intromissão do pênis não implica em inseminação. P. lynceus exibe cópula traumática, na qual parceiros consomem cerata um do outro durante a cópula, um fenômeno inédito dentre as complexas estratégias reprodutivas de hermafroditas Sexual selection is pervasive and shapes reproductive traits. Many hermaphrodites have organs for sperm storage and digestion, which are potentially involved in post-copulatory sexual selection mechanisms such as sperm competition and cryptic \"female\" choice. In animals with internal fertilization, these processes occur within the female reproductive tract, thus the knowledge of its functional morphology is of utmost importance for understanding post-copulatory mechanisms of sexual selection. Most sea slugs are hermaphrodites and have a complex reproductive system, with organs for sperm storage and digestion. In this context, the present study aimed to investigate the mating behavior and the functional morphology of the sperm-containing chambers of the reproductive tract of the nudibranch Okenia polycerelloides (Ortea & Bouchet 1983), and the mating behavior of the nudibranch Phydiana lynceus Bergh 1867. First, we have applied different microscopy techniques (light, confocal and transmission electron microscopy) to study the sperm-containing chambers of O. polycerelloides. Then, we have combined experimental manipulations and histological analyses to investigate the fate of sperm within the female reproductive tract after one and two subsequent matings, and if starvation influences the occurrence of sperm digestion. Sperm was received and stored by the seminal receptacle, while the bursa copulatrix had a digestive function. Multiple mating events could lead to sperm stratification in the seminal receptacle. Although starvation seemed to intensify sperm digestion in the bursa copualtrix, it did not determine its occurrence. Sperm digestion occurred continuously, and at least some amount of sperm received during each mating event was directed to the bursa copulatrix to be digested, corroborating a previous hypothesis of surplus sperm digestion. However, all received sperm could also be directed to the bursa copulatrix, suggesting the possibility of cryptic female choice. Gradual reduction of the contents of the bursa copulatrix with increasing post-copulation times suggests resorption of the digested gametes. Mating interactions in O. polycerelloides initiated by mutual contact using the oral region, followed by body alignment, penis intromission, and sperm transfer. However, interactions could end at any of these stages, and even penis intromission did not guarantee insemination. Phidiana lynceus exhibited traumatic mating, in which partners consume cerata from one another before sperm exchange, clearly adding to the complexity of mating strategies in hermaphrodites

The polyclad Pericelis cata has been reported in two distinct localities along the North Atlantic: Curaçao and the Caribbean coast of Colombia. Recently identified from the Southwestern Atlantic, the species was first described from the Cabo Frio region (23°S) (Rio de Janeiro State), a transitional zone between warm and cold water species located southeastern Brazil. The second location is in the northeastern coast in warm waters, in the entrance of the Todos-os-Santos Bay, a geographic area within the Brazilian Biotic Province, an important center of marine biodiversity of the Tropical Atlantic.

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.

The crabs of the genus Dissodactylus are well known as ectosymbionts of irregular echinoids belonging to Clypeasteroida and Spatangoida. Dissodactylus crinitichelis is the only species of the genus reported in Brazil. The pea crab species has been already recorded associated with four species of echinoids in Brazilian waters. This paper reviews the known hosts for D. crinitichelis and registers for the first time the association between the pea crab and the sand dollar Leodia sexiesperforata increasing to five the number of known hosts for the crab.

The nudibranch Flabellina dana Millen and Hamann, 2006 is reported from two localities in the northeastern Brazilian coast. These are the first records of this species, previously recorded from localities in the Bahamas and the Caribbean Sea, in South Atlantic Ocean, extending its known geographic distribution more than 3500 km southward.

Although around 3,000 species of nudibranchs are known worldwide, only nearly 100 species are reported from Brazil. From Bahia State, northeastern Brazil, only seven species are listed. The current article provides four new records of nudibranchs from this region: Geitodoris pusae (Marcus 1955); Felimida paulomarcioi (Domínguez, García and Troncoso 2006); Felimida binza (Marcus and Marcus 1963) and Cadlina rumia Marcus 1955. The new records presented herein fill part of a historical gap in the species geographic distribution, and increase to eleven the number of nudibranch species known from Bahia.