Aquatic oligochaeta ( Annelida : Clitellata ) in extractive reserve Lake Cuniã , Western Brazilian Amazon

Oligochaeta is one of the most common and abundant taxon in continental aquatic fauna. However, knowledge of their distribution in Brazilian ecosystems is still incomplete and fragmented. Thus, the aim of this study was to develop an inventory of aquatic oligochaetes in the Extractive Reserve of Lake Cuniã in the State of Rondônia, Brazil. Collections of data were performed during the dry (August 2015) and rainy seasons (February 2016). The sediment samples were collected near the lakeside region using the kick sampling method and a kick-net sampler (mesh size of 0.25mm). This paper provides a catalog with 12 taxon from a total of 383 specimens, distributed into two families: Naididae (95.08%) and Opistocystidae (4.92%). The Pristininae subfamily was the most significant (85.68%), followed by subfamilies: Naidinae (8.36%), Tubificinae (0.52%) and Rhyacondrilinae (0.52%). In addition, some species such as Allonais inaequalis, Aulophorus furcatus, Dero nivea, Pristina synclites, Pristina menoni and Opistocysta serrata, were recorded for the first time in the Brazilian Amazon region. Therefore, the results of this study contribute to increase knowledge on the distribution of the Oligochaeta class in Brazil, particularly in the North of the country, which is so extensive and rich in water resources, but not extensively studied.


Introduction
Even though tropical regions are considered the most important in biodiversity, the biotas of these areas are rarely explored and still possess many undescribed species (Lewinsohn & Prado, 2005).In this context, Brazilian invertebrate diversity remains largely unknown, mainly because some groups receive more attention than others (Hortal et al. 2015) and the difficulties in taxonomic identification discourage the development of new studies.This results in fragmented and scarce information on the invertebrate fauna (Magurran, 2011), especially in continental aquatic ecosystems, where the information about this group is even more incomplete (Agostinho et al. 2005).
However, despite the importance of Oligochaeta in the dynamics of aquatic environments, there have been few scientific studies focused on registering these organisms in Brazilian ecosystems (Gorni & Alves, 2008b).Consequently, Christofferson (2010) affirms that studies on oligochaetes in South America are a pioneer phase.
In the Brazilian Amazon, Du Bois-Reymond Marcus (1947;1949a;1949b) and Marcus (1942;1943;1944) were the first researchers to register many of the species known in scientific literature.Eventually, some species of Oligochaeta were recorded by Imler (1989) and Collado & Schmelz (2000;2001).Similarly, organisms of this class have been identified in the Ecuadorian Amazon (Turcotte & Harper, 1982) and Colombian Amazon (Carvajal et al., 2009).However, studies on the Amazon aquatic macrofauna have not evolved to present specific levels of species identification (Cleto-Filho & Walker, 2001, Lopes et al. 2011, Aviz et al. 2012).
This study provides a checklist of aquatic oligochaete in The Extractive Reserve of Lake Cuniã -Rondônia, in the Western Brazilian Amazon, and proposes a catalog of the local species found and their ecological information.

Area of Study
This study was conducted in the Extractive Reserve of Lake Cuniã (Figure 1), located about 130 kilometers from Porto Velho, on the left bank of the lower Madeira River.With an area of approximately 55.850 hectares, the Reserve has two distinct areas.The first is formed by a piece of land that has a diverse environment with high biodiversity and the second is a floodplain area with seasonal water flow throughout the year.The wet season occurs from November to April and the dry season from May to October.
Samples were oxygenated with aquarium pumps to maintain the organisms living during the screening process.For organism selection, small portions of the samples were put into translucent trays containing water and subsequently fixed in 10% formalin and preserved in 70% alcohol (Alves & Gorni, 2007).Semi-permanent slides were prepared and the taxonomic criteria adopted by Righi (1984) and Brinkhurst & Marchese (1989) were followed in order to identify Oligochaeta.The identified specimens were deposited in the Zoological Collection of the University of Araraquara (UNIARA).Water temperature, dissolved oxygen, pH and electrical conductivity were measured in each site of the lake with a multiparameter sensor (YSI 5560).The concentrations of organic matter were determined by mass loss.For this purpose, sediment samples were dried for 12 hours at 60 °C and then ignited at 550 °C for 5 h, according to Maitland (1979).
Information on oligochaeta species in Brazil were searched for in the following databases: Scopus, Google Scholar, and Scielo, with no date filter.Papers by Marcus (1942Marcus ( , 1943Marcus ( , 1944) ) and Christoffersen (2007) were also consulted for obtaining additional data.

Results
The dissolved oxygen in the rainy season reached a maximum of 5.250 mg/L in S5, while the minimum for the dry season was 1.950 mg/L in S6.The oxygen concentration measured in the Cuniã Lake followed a pattern previously found by Almeida & Melo (2009) in Amazon lakes.Temperature was high, electrical conductivity was low, especially during the dry season, and the pH was acid at all sites of the lake.Regarding organic matter, sites S6 and S7 presented the highest concentrations throughout the year and presented a small increase during the rainy season (Table 1).
The Dero sp.species was only collected in dry season samples, but we were not able to properly count the number of gills, making it impossible to identify the species level.Similarly, the Bothrioneurum sp.species and immature tubificinae were not identified at more specific levels.Pristina sp.1 showed a different dorsal needle setae compared to the species already described in literature, and may be a new species of the genus.
Aulophorus costatus Du Bois-Reymond Marcus,1944 (Figure 2c) Its main characteristic is the palmate dorsal needle seta and gill cavity with two pairs of gills (Brinkhurst & Marchese, 1989).Registration in Brazil has already occurred in the States of Amazonas and Pará, as well as in São Paulo, in association with other organisms such as macrophytes (Alves & Gorni, 2007) and sponge specimens (Gorni & Alves, 2008a).

Dero nivea Aiyer 1930 (Figure 2e)
This species is cosmopolitan and is mainly characterized by its prolonged gill cavity (Brinkhurst & Marchese, 1989).Its incidence in Brazil is more significant in the State of São Paulo, but has also been recorded in Rio Grande do Sul.Like other species of Oligochaeta, it can live in association with other organisms, but is especially found on aquatic vegetation (Correia & Trivinho-Strixino, 1998, Trivinho-Strixino et al. 2000, Alves & Gorni, 2007).

Pristina synclites
Stephenson, 1925 (Figure 2f) The records of this species occurrence are in the State of São Paulo, where it was found in urban streams with low concentration of dissolved oxygen (Alves et al. 2006) and in organically enriched reservoirs (Fusari & Fonseca-Gessner, 2006).
Pristina menoni (Aiyer, 1929) (Figure 2g) Species with records only in São Paulo and Paraná.It has been recorded that it associates with bryophytes (Gorni & Alves, 2007).It has also been found in urban stream waters in São Paulo (Alves et al. 2006) and in the Ivinhema River in Paraná (Montanholi- Martins and Takeda, 2001).

Bothrioneurum sp. (Figure 2h)
This genus is mainly characterized by the presence of a sensitive organ in the prostomium and the presence of an external spermatophore (Brinkhurst & Marchese, 1989).Its occurrence has been cataloged in the States of São Paulo, Minas Gerais, Amazonas, Pará and Rio Grande do Sul.It also occurs mainly in the sediments of degraded sites (Alves & Lucca, 2000;Suriani et al. 2007) and in the streams of preserved areas (Rodrigues et al. 2013).In the south of the country, it has been collected in rice fields (Stenert et al. 2012).In the Amazon region, it was found in Pará, near the County of Belterra, by Marcus (1942) and Du Boys-Reymond Marcus (1947, 1949aand 1949b) and in Central Amazon by Irmler (1989) and Collado & Schmelz (2000;2001).Harman, 1970 (Figure 2i, j) Serrate hair seta, the presence of proboscis and three (one median and two lateral) caudal appendages (Brinkhurst & Marchese, 1989) characterize this species.In Brazil it was collected only in the States of Paraná (Montanholi- Martins & Takeda, 2001) and Mato Grosso do Sul (Takeda et al., 2000).

Discussion
This study showed the occurrence of 12 taxa, representing approximately 13.95% of 86 species registered in Brazil (Christoffersen, 2007).In addition, this was the first registration of some species, such as Allonais inaequalis, Aulophorus furcatus, Dero nivea, Pristina synclites, Pristina menoni and Opistocysta serrata, in the Brazilian Amazon region.According to Christoffersen (2010) the catalogued oligochaetes from South America represent only a fraction of their true diversity, which emphasizes the need for more studies that contemplate species inventory in neotropical regions.Most of the global biodiversity data still comes from temperate regions and refer mainly to important and economically valuable taxa.These shortfalls in biodiversity information need to be recognized and quantified for more accurate conservation assessments and actions (Hortal et al. 2015).
In the aquatic community of Oligochaeta, the Naididae family stands out as the most abundant and diverse, consisting of eight subfamilies and comprising about 50% of the described species on the planet (Rodriguez & Reynoldson, 2011).Moreover, according to Martin (1996) Naididae is a cosmopolitan family, which is very common in lakes.In this study, this family was the most abundant (95.08%), mainly represented by the Pristininae subfamily (85.68%).Some species are periphytic naidids (Pristina), some have gills and respiratory appendages that allow inhabiting systems where oxygen is a limiting factor (Dero, Aulophorus) and others are more often found in sediment (Tubificinae, Bothrioneurum) (Martin, 1996).From a regional perspective, the State of São Paulo has the highest species richness, with 75 species recorded (Gorni et al. 2015), but little is known about these species in other Brazilian States, which reinforces the importance of studies that seek to verify the occurrence of Oligochaeta in other places.Only recent inventories conducted in States, such as Minas Gerais (Rodrigues et al. 2013) and Rio Grande do Sul (Stenert et al. 2012) have started to change this scenario.
The results of this research will contribute to increase knowledge on Oligochaeta in tropical ecosystems, since some species were reported for the first time in the Western Brazilian Amazon.In this context, it is important to promote other biodiversity studies in areas with difficult access, because according to Hortal et al. (2007) species inventories are more frequent in places that offer more research infrastructure and logistics.

Figure 1 .
Figure 1.Location of Extractive Reserve Lake Cuniã in the state of Rondônia, Brazil.Source: Own author (2016)

Table 2 :
Oligoqueta taxa registered in the Extractive Reserve Lake Cuniã.