Ultrastructural analysis of the shells of Anodontites trapesialis (Lamarck) and Anodontites elongatus (Swaison) (Mollusca, Bivalvia, Etherioidea) from the Mato Grosso Pantanal Region, Brazil

Abstract

ABSTRACT. Based on optical and SEM microscopic observations, the projections of the outer surface of the periostracum and inner micro-structures of the shell are described and redefined. The outer surface of the periostracum is practically smooth in both species. Considering a mesoscopic view of the periostracum, A. trapesialis (Lamarck, 1819) presents regular corrugations in the form of radial sequences of arches on the disk region, isolated rays or horizontal sequences of rays on the anterior lower region. A. elongatus presents corrugations formed by series of oblique arches on the disc and oblique rays on the carina. Under SEM, micro ridges were more evident in A. elongatus, but a wide diversity of shapes and patterns of micro fringes were observed in A. trapesialis, especially in young individuals. Considering the profile of the shell layers, the periostracum is relatively thin and apparently simple in A. trapesialis and thinner in A. elongatus. The prismatic layer is thick in both species, consisting of a single series of elongated prisms and wedge-shaped prisms close to the outer surface. The nacreous layer consists of very fine lamellae without pattern or with a slight staircase-like; in A. elongatus this layer is divided by a laminar inclusion of conchiolin. The fringes are abundant and diversified in A. trapesialis, a species less resistant to desiccation due to the presence of a wide intervalvar gap. The existence of a greater density of micro fringes and spikes in juveniles may be related to the orientation of the animal in order to search for an ideal site for development or for escape from regions subject to seasonal droughts, like Pantanal. KEY WORDS. Mycetopodidae, periostracum projections, shell layers.

Variability, function and phylogenetic significance of periostracal microprojections in unionoid bivalves (Mollusca)

“…Similarly, exclusiveness of microfringes to the mycetopodids could indicate evolution of this shell character just before this family branched off from the remaining unionoids. Our dataset can be extended by observations on one additional mycetopodid species by Callil and Mansur (2005), who found similar microridges and microfringes in A. elongatus . As these conclusions are drawn from just two iridinid and two mycetopodid species of only one genus, respectively, it will be important and interesting to determine whether other genera of these unionoid families exhibit the same morphologic traits.…”

“…1b). For more detailed morphological description of both microfringes and microridges in A. trapesialis and Anodontites elongatus (Swaison, 1823), see Callil and Mansur (2005).…”

“…With respect to the Unionoida, we are aware of merely a single paper using high magnification (electron) microscopy to describe periostracal microprojections in two species of Anodontites , belonging to the family Mycetopodidae (Callil and Mansur 2005). Based on their observations on this one genus, these authors classified periostracum projections into four size‐related types: (1) macroscopically visible ‘folds’, (2) mesoscopically visible ‘corrugations’, (3) ‘microridges’ and (4) ‘microfringes’ and ‘spikes’.…”

Freshwater mussels from South America: state of the art of Unionida, specially Rhipidodontini

“…A greater increase in knowledge about freshwater mussel fauna began with the works of Mansur (1970) that presented the catalog of Hyriidae and Mycetopodidae of the state of Rio Grande do Sul. She published works dealing with specimens from southern Brazil (Mansur 1972, Mansur & Anflor 1982, Mansur & Pereira 2006 as well as from the Amazon River basin (Mansur & Valer 1992, Mansur & Pimpão 2008, Pimpão & Mansur 2009) and Pantanal (Serrano et al 1998, Callil & Mansur 2005, 2007. There are also two technical works, one identifying Southern and Southeastern genera of mussels (Mansur et al 1987) and another on how to obtain and identify glochidia (Mansur & Campos-Velho 1991).…”

Anodontites trapesialis (LAMARCK, 1819): um bivalve parasito de peixes de água doce

“…Na América do Sul a maior parte dos estudos sobre os membros destas superfamílias é voltada aos aspectos anatômicos, morfológicos funcionais e à sistemática (MARSHALL, 1922;BONETTO, 1967;VEITENHEIMER-MENDES, 1973a, 1973bMANSUR, 1974;HEBLING, 1976;SCHULZ;GARCES, 1987;CASTELLANOS;LANDONI, 1990;AVELAR, 1993;SIMONE, 1994;OLAZARRI, 1995;MANSUR, 2005;PEREIRA, 2006). Muitos dos trabalhos que fazem referência aos aspectos reprodutivos reportam-se principalmente à família Hyriidae, que possui larva do tipo glochidium (PEREDO; PARADA, 1986;AVELAR et al, 1991;AVELAR;MENDONÇA, 1998;MANSUR, 1999;BEASLEY et al, 2000).…”