Anatomy and Functional Morphology of the Southwestern Atlantic bivalve Mactra isabelleana d´Orbigny, 1846 (Heterodonta: Mactridae)

JAVIER H. SIGNORELLI ; GUIDO PASTORINO

Organisms Diversity and Evolution Electronic Supplement

SPRINGER HEIDELBERG

Año: 2006 vol. 6 p. 70 - 70

1615-9640

The main objective of this project is the study of thefunctional morphology of Mactra isabelleana. Thissandy-bottom bivalve is one of the most frequent alongthe coast of Buenos Aires province. It occurs from Riode Janeiro, Brazil to Golfo San Matías, Argentina (1).Its anatomy is described using a stereoscopicmicroscope and traditional histology.A trigonal shell with growth lines over the entire surfaceand a thin and brownish periostracum are the mainexternal features. The ultrastructure of the aragoniticshell consists of two layers; the outer, cross-lamellar(CL) layer is constituted of very thin lamellae; the innerlayer is finer and with a complex CL structure. Twoanterior and two posterior lateral teeth are present in theright valve hinge, which also has two V-shaped cardinalteeth. In the left valve hinge there are two lateral teeth;the posterior one and the anterior one with accessorylamellae, and two V-shape cardinal teeth with accessorylamellae flanking the chondrophore. The umbo isorthogyrate and the external posterodorsal ligament ispresent. The digestive system and mantle cavity organsare illustrated and described to explain the food current.The siphons are of the type C of Yonge (2). Thestomach is of the type V of Purchon (3). The ctenidiaare connected at the posterior end, surrounding thebody. Each ctenidium consists of a inner and outerdemibranch with a supra-axial outer demibranch. Theyare apparently of the type C(2) of Atkins. The labialpalps are triangular with the inner faces plicated andouter faces smooth and their relationship with thectenidium belong in category III of Stasek. Preliminaryanatomy of this species of Southwestern AtlanticMactridae basically agrees with previous studies.