A new occurrence of Anodontites tenebricosus (Bivalvia: Mycetopodidae) in the Sapucaí river basin, São Paulo, Brazil: environmental and conchological aspects Troncon, EK.* and Avelar, WEP.* Laboratório de Malacologia, Departamento de Biologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo – USP, Av. Bandeirantes, 3900, CEP 14040-901, Ribeirão Preto, SP, Brazil *e-mail: [email protected]; [email protected] Received July 7, 2010 – Accepted September 1, 2010 – Distributed – August 31, 2011 (With 6 figures) Abstract The aim of this work was to register the occurrence of Anodontites tenebricosus (Bivalvia: Mycetopodidae) in the Sapucaí river basin, municipality of São Joaquim da Barra, São Paulo state, Brazil, associating its occurrence to the environment in which they are found, besides providing conchological data to contribute to the identification of the species. Fifty one specimens of Anodontites tenebricosus were studied regarding their conchological and morphometrical aspects. Strong correlations were found between the morphometric variables, the correlation between ‘length and height of the shell’ being the most significant. The characteristics of the shells ofA. tenebricosus found in the Sapucaí river basin resemble the descriptions of the species found in the literature; therefore, we are able to expand the area of occurrence of the species for the state of São Paulo. Keywords: Bivalvia, Mycetopodidae, Anodontites tenebricosus, conchology, sedimentology. Nova ocorrência de Anodontites tenebricosus (Bivalvia: Mycetopodidae) na bacia do rio Sapucaí, São Paulo, Brasil: aspectos ambientais e conquiliológicos Resumo Os objetivos deste trabalho foram registrar a ocorrência de Anodontites tenebricosus (Bivalvia: Mycetopodidae) na bacia do rio Sapucaí, no município de São Joaquim da Barra, estado de São Paulo, Brasil, associando sua ocorrência ao ambiente em que são encontrados, além de fornecer dados conquiliológicos que contribuem para a identificação da espécie. Cinquenta e um espécimes de Anodontites tenebricosus foram estudados sob aspectos conquiliológicos e morfométricos. Foram encontradas fortes correlações entre as variáveis, sendo a correlação entre “comprimento e altura da concha” a mais significativa. As características das conchas deA. tenebricosus encontradas na bacia do rio Sapucaí assemelham-se às descrições da espécie na literatura; podemos, assim, ampliar a área de ocorrência da espécie para o estado de São Paulo. Palavras-chave: Bivalvia, Mycetopodidae, Anodontites tenebricosus, conquiliologia, sedimentologia. 1. Introduction Not a large number of limnic bivalves have been studied beyond the loss of the species per se (Vaughn and Taylor, in the state of São Paulo and they are rarely mentioned in 1999). Since they play an important role in the functioning the literature, in spite of their importance as significant of lotic and lentic ecossystems, the importance of studies components of freshwater ecossystems, in the recycling regarding aspects of biology, anatomy and ecology of of nutrients, and as entities capable of providing reliable freshwater bivalve native fauna is justified. evidence of pollutants in limnic watersheds (Vaughn In Brazil, the freshwater bivalves are represented by and Taylor, 1999). However, they are the most seriously the orders Unionoida and Veneroida. The first includes the endangered group of freshwater organisms. The main families Mycetopodidae and Hyriidae, while the second causes for that include anthropogenic activities, such as includes the families Dreissenidae, Pisidiidae and, more building dams, pollution and toxicity of the sediment, as recently, Corbiculidae and Mytilidae, being these latter well as the introduction of exotic species (Bogan, 1993; represented, respectively, by the asiatic species Corbicula Lydeard et al., 2004). Therefore, the consequences of fluminea (Müller, 1774) and Limnoperna fortunei (Dunker, bivalve population decline in the fauna of the rivers go 1857) (Simone, 2006). Braz. J. Biol., 2011, vol. 71, no. 3, p. 629-637 629 Troncon, EK. and Avelar, WEP. According to Castellanos and Landoni (1990), the conductivity and turbidity of the water were considered, Mycetopodidae family (Gray, 1940) is restricted to South aiming for the determination of the association between America, not being found in the Andean-Patagonian region, the physical and chemical data obtained in this study. and occurs in lentic and lotic environments. They are found Sediment samples from the river bottom were also partially buried in sediment of variable particle sizes and collected from September 2007 to January 2008 in order they feed on particles in suspension, such as plankton and to perform particle size analysis and determination of organic detritus. In Brazil, the family is represented by 12 organic matter content. The sediment was placed in genera and the genus Anodontites represents the largest properly labelled plastic bags and was transported to the number of species (15) (Simone, 2006). laboratory in ice coolers. Taking the Mycetopodidade family into consideration, Portions of the collected sediment, preserved in a the following species were registered in the state of São freezer, went through the process of drying in an oven Paulo: Fossula fossiculifera (Orbigny, 1835) (Avelar, at 60 °C to obtain the dry weight. However, the drying 1993), Anodontites trapesialis (Lamarck, 1819) (Hebling, time of the sediment is not defined because the samples 1976), A. trapezeus (Spix, 1827) (Hebling, 1976) and are collected from submerged surface horizon, and the A. soleniformis (Orbigny, 1835) (Avelar and Cunha, 2001). quantity of water varies in each sample. After the drying The aim of this study was to register the occurrence of process, 50 g of the sample were sieved and separated by Anodontites tenebricosus (Lea, 1834) in the Sapucaí river the method of quartering (Muehe, 1996). According to basin, municipality of São Joaquim da Barra, São Paulo this method, the sample is poured onto a surface forming state, Brazil, as well as to provide conchological data that a cone. This cone is divided into four equal parts and two contribute to the species’ identification, associating its parts are used, being opposite to each other. This procedure occurence with the environment in which they are found. is repeated until obtaining the desired weight sample. The remaining 50 g are then sieved for 15 minutes on the 2. Material and Methods shaker sieve, which is previously calibrated according to standard methodology. The material retained on each sieve 2.1. Study area and methodology for collecting animals was weighed on an electronic scale (precision 0.001 g) and The study was conducted in the Sapucaí river identified according to Wentworth´s scale for particle size basin, municipality of São Joaquim da Barra, SP, Brazil of sediment (Wentworth, 1922). (20° 30’ 49,7” S; 47° 50’ 10,2” W), which, according to data Quantification of organic matter present in the sediment from CETESB (Companhia de Tecnologia de Saneamento was determined by burning 10 g of material in an oven Ambiental, 2007), is part of the Sapucaí/Grande basin. at 500 °C for three hours, and the difference between the The animals were collected monthly, from August initial and final mass represents the amount of organic 2007 to January 2008. Living specimens and valves of matter present in the sample. Anodontites tenebricosus were located in the Sapucaí river by touching the river bottom with the hands and removing 3. Results rocks and pebbles while looking for the animals. When found, they were collected and taken to the laboratory in 3.1. Animals: morphology and morphometry of the shell coolers containing water from the river, for conchological Fifty-one specimens of Anodontites tenebricosus were and morphological studies. sampled in the Sapucaí river (Figure 1), being most of For the shell studies, a digital calliper was used and the them found in the middle of the river, within a distance of following measures were taken: length (greater distance about 20 m from the shore. It should be pointed out that between the anterior and the posterior axis of the shell), the animals were always found in areas of rapids, partially height (distance between the ventral and dorsal axis of buried in the sediment, and protected by rocks and pebbles. the shell, passing through the umbonal region), width The shells of A. tenebricosus (Figures 2) are elliptical or (distance between the two valves, with the shell closed, reniform, thin and with a strong ventral deflexion in most of also passing through the umbonal region) and length of the specimens. The periostracum is dark, brownish-green, the ligament. Furthermore, the correlations between the opaque and usually eroded, especially in the umbo area morphometric variables were examined using Pearson’s (u). Sculpture of the periostracum slightly checkered and Correlation Coefficient (r). it varies depending on the region of the shell (Figure 3). Ten specimens were deposited as vouchers in the In the posterior dorsal region, 5 to 6 radial lines (rl), not Museum of Zoology at the University of São Paulo prominent in some specimens, raise from the umbonal (MZSP 96618). region toward the posterior end. The ligament (l) is long, thin, with a triangular shape ligamental sinus (ls). 2.2. Temperature, abiotic factors of the water and The inner surface of the shell presents brown colouration, sedimentology mixed with bluish-white iridescent shade. The umbonal