Microturbellarians (Platyhelminthes and Acoelomorpha) in Brazil: invisible organisms? / Microturbelários (Platyhelminthes e Acoelomorpha) no Brasil: organismos invisíveis?

Abstract Microturbellarians typically belong to the benthos and may occur in a wide variety of environments. They are abundant in freshwater and marine ecosystems and may occur in moist terrestrial habitats. However, turbellarians are seldom taken into account in studies of biodiversity. Most studies on Brazilian microturbellarians had taxonomical purposes and were done in the years 1940-1950. Thus, information on their occurrence and ecological aspects are dispersed throughout several papers. We intend here to summarize the biogeographical distribution and ecological aspects of microturbellarians recorded for Brazil, indicating the main gaps in their knowledge and possible actions to enhance studies on this group. There are 239 species of microturbellarians registered for Brazil, with records distributed in 12 states. However, just three states located in southern Brazil have records of 94% of microturbellarian species. Thus, knowledge on the systematics and geographical distribution of Brazilian microturbellarians clearly reflect the scientific activity over many years or decades in two states of southeastern and southern Brazil. Considering the scant information on this group in Brazil, which is also the situation of the Neotropical microturbellarians in general, some actions should be proposed. First, it would be necessary to sample in the diverse biomes, as well as in the various river and sea basins, based on standardized sampling protocols. Second, it would be necessary to encourage diverse research groups to include microturbellarians and/or turbellarians in general into biodiversity inventories and studies on community structure of invertebrates. Third, it is necessary to increase the number of research groups on microturbellarians, in order to augment the studies on their morphology, systematics, and ecology. Considering their abundance, species richness and ecological importance in aquatic environments, despite some peculiarities regarding their sampling, sorting and identification procedures, the challenge to study microturbellarians and enhance knowledge about them in Brazilian ecosystems should be faced.

Resumo Microturbelários são tipicamente bentônicos e podem ocorrer em uma ampla variedade de ambientes. São abundantes em ecossistemas marinhos e de água doce, podendo ocorrer em ambientes terrestres úmidos. Entretanto, turbelários raramente são considerados em estudos de diversidade. A maioria dos estudos sobre microturbelários brasileiros tiveram propósito taxonômico e foram realizados nos anos 1940-1950. Assim, informações sobre ocorrência e aspectos ecológicos estão dispersos em diversos artigos. O objetivo deste trabalho é sumarizar a distribuição biogeográfica e aspectos ecológicos dos microturbelários registrados para o Brasil, indicando as principais lacunas do conhecimento e possíveis ações para ampliar estudos sobre esse grupo. Há 239 espécies de microturbelários registradas no Brasil, com registros distribuídos em 12 estados. No entanto, 94% das espécies de microturbelários foram registradas em apenas três estados localizados no sul e sudeste do Brasil. Assim, o conhecimento sobre a sistemática e distribuição geográfica dos microturbelários claramente reflete as atividades científicas realizadas por muitos anos ou mesmo décadas em dois estados do sudeste e sul do Brasil. Considerando as escassas informações existentes sobre esse grupo no Brasil, assim como a situação dos microturbelários neotropicais em geral, algumas ações devem ser propostas. Primeiramente, é necessário realizar amostragens em diversos biomas, assim como nas várias bacias e regiões hidrográficas marinhas, baseadas em protocolos de amostragem padronizados. Em segundo lugar, faz-se necessário incentivar diversos grupos de pesquisa a incluir microturbelários e/ou turbelários em geral em inventários da biodiversidade e estudos de estrutura de comunidades de invertebrados. Em terceiro lugar, é necessário ampliar o número de grupos de pesquisa em microturbelários, para aumentar os estudos sobre sua morfologia, sistemática e ecologia. Considerando sua abundância, riqueza de espécies e importância ecológica em ambientes aquáticos, apesar de suas peculiaridades de amostragem, triagem e identificação, o desafio de estudar e ampliar o conhecimento sobre microturbelários em ecossistemas brasileiros deve ser enfrentado.

Microturbellarians (Platyhelminthes and Acoelomorpha) in Brazil: invisible organisms?

Microturbellarians typically belong to the benthos and may occur in a wide variety of environments. They are abundant in freshwater and marine ecosystems and may occur in moist terrestrial habitats. However, turbellarians are seldom taken into account in studies of biodiversity. Most studies on Brazilian microturbellarians had taxonomical purposes and were done in the years 1940-1950. Thus, information on their occurrence and ecological aspects are dispersed throughout several papers. We intend here to summarize the biogeographical distribution and ecological aspects of microturbellarians recorded for Brazil, indicating the main gaps in their knowledge and possible actions to enhance studies on this group. There are 239 species of microturbellarians registered for Brazil, with records distributed in 12 states. However, just three states located in southern Brazil have records of 94% of microturbellarian species. Thus, knowledge on the systematics and geographical distribution of Brazilian microturbellarians clearly reflect the scientific activity over many years or decades in two states of southeastern and southern Brazil. Considering the scant information on this group in Brazil, which is also the situation of the Neotropical microturbellarians in general, some actions should be proposed. First, it would be necessary to sample in the diverse biomes, as well as in the various river and sea basins, based on standardized sampling protocols. Second, it would be necessary to encourage diverse research groups to include microturbellarians and/or turbellarians in general into biodiversity inventories and studies on community structure of invertebrates. Third, it is necessary to increase the number of research groups on microturbellarians, in order to augment the studies on their morphology, systematics, and ecology. Considering their abundance, species richness and ecological importance in aquatic environments, despite some peculiarities regarding their sampling, sorting and identification procedures, the challenge to study microturbellarians and enhance knowledge about them in Brazilian ecosystems should be faced.

Metazoan symbionts of the yellow clam, Mesodesma donacium (Bivalvia), in southern Chile: geographical variations.

Mesodesma donacium is a dominant species on sandy beaches along the Chilean coast. However, the only previous parasite records for this species were obtained for the northern Chilean coast (20° S-33° S), which dealt with cestodes, polychaetes, and copepods. In this study, the symbiotic fauna of M. donacium in its southern distributional range is reported, and the geographical variations in the occurrence of this fauna are evaluated. A total of 565 individuals of M. donacium were captured by local fishermen from 5 localities: Mehuín (MEH) (39° 26' S), Carelmapu (CAR) (41° 44' S), Ancud (ANC) (41° 53' S), Cucao (CUC) (42° 35' S), and Quellón (QUE) (43° 24' S), covering a total distance of 450 km. To collect metazoan symbionts, the valves, mantle, gills, gonad, and digestive gland of each specimen of yellow clam were examined, and symbiont identifications were made via morphological and genetic analyses. The prevalence and mean intensity of infestation were calculated for each symbiotic species. Univariate and multivariate analyses were performed to evaluate the differences in symbiotic load between localities. Seven metazoan symbiotic species were recorded. The most abundant species were Paranthessius mesodesmatis, Monorchiidae gen. sp., and Paravortex sp. The copepod P. mesodesmatis and metacercaria Monorchiidae gen. sp. showed a high prevalence in all localities, but their intensity of infection varied among localities. The turbellarian Paravortex sp. was most frequently associated with ANC and CUC. The digenean Sanguinicolidae gen. sp. was recorded only at CAR, and the polychaete Spionidae gen. sp. was recorded only at MEH. In its southern distributional range, M. donacium was characterized by an absence of cestodes. This absence can be explained by the absence of the definitive host. The local environmental conditions in the southern range of the host could explain the differences in symbiotic composition among localities.

Parasites of the pleasure oyster Crassostrea corteziensis cultured in Nayarit, Mexico.

The pleasure oyster Crassostrea corteziensis is collected and cultured in Nayarit on the Pacific coast of Mexico, and the improvement and promotion of its culture are seen as a possible source for the economic development of coastal populations. However, information about the parasite fauna of the pleasure oyster is almost completely lacking. A histopathological survey carried out in two estuaries, Boca del Camichín and Pozo Chino, revealed the presence of hypertrophied gametes, rickettsiales-like prokaryotes (RLPs), the protozoan Perkinsus marinus, a protozoan Nematopsis sp., Ancistrocoma-like ciliates (ALCs), Sphenophrya-like ciliates, a turbellarian Urastoma sp., and encysted crustaceans. In general, prevalence and intensity of parasites were similar in both localities except that ALCs and encysted crustaceans were more prevalent in Pozo Chino than in Boca del Camichín. Perkinsus marinus and RLPs seem to represent a more significant risk for the health of pleasure oysters than do the other parasites, and surveillance and control of these parasites are needed for the development of pleasure oyster culture.

The first ultrastructural description of the Haswell cells in Temnocephalidae (Platyhelminthes, Temnocephalida), with insights into their function.

This paper provides the first description of the Haswell cells at the ultrastructural level, as well as giving an insight into their function. Two species of Temnocephalidae were studied, Temnocephala iheringi and T. haswelli. Haswell cells are identical in both species, and their structure indicates that they have a secretory function. They are highly interdigitated with parenchymal cells and are usually joined to them by cup-like desmosomes. Nuclei are irregular, with a honeycomb structure and perichromatin granules. The most prominent organelle is granular endoplasmic reticulum, which is typically arranged in concentric rings that usually encircle a conspicuous Golgi complex. Secretion bodies are secreted via projections of the Haswell cells that reach the surface in the anterior portion of the body and in the tentacles. Distinct pores with a size and distribution consistent with the TEM observations were seen under SEM in these regions.

Labelling of the platyhelminth Dugesia tigrina with 99mtechnetium.

The study of the labelling of planaria with 99mTc shows that the incorporation of radioactivity in this platyhelminth increases with an increase in SnCl2 concentration from 0.13 to 1.3 microM, reaching a plateau in the range of 1.3-130 microM then decreasing with 1300 microM. At concentrations of 1.3 and 13 microM SnCl2, a stronger binding of 99mTc was obtained. The biological viability of the labelled planaria was not altered when the described methodology was used. The advantage of this new labelling technique is that it is possible to obtain a platyhelminth preparation labelled with a radionuclide that is very cheap, is easily available and is a gamma emitter with a photon energy of 140 keV.