FAUNA PARAGUAY MOLLUSC IMAGE GALLERY
FAUNA PARAGUAY MOLLUSCA
The Phylum Mollusca (Latin for "soft nut or fungus") has no distinct affinity to any other living group, though they retain a certain resemblance to the flatworms. They have radiated into a huge diversity of body forms. Molluscs have the following characteristics in common:
º Bilateral symmetry.
º Through gut.
º Lack body cavity other than that provided by blood sinuses.
º Body monomeric, squat and often elongated with a large, flat foot and an anterior head bearing eyes and sensory tentacles.
º Protective extrenal dorsal shell composed of protein conchiolin.
º Tongue-like, chitinous, toothed "radula" rasps particles which are then winched into the mouth via a mucus cord.
º Gas exchange via ctenidial gills in the mantle cavity.
º Open blood system and heart in pericardial cavity.
º Nervous system with two pairs of longitudinal, ganglionic cords.
º Single pair of gonads that discharge into the mantle cavity.
º Eggs cleave spirally
º Development indirect via larval stages.
The Mollusca are the second most speciose animal phylum on the planet and owe their success to their plasticity of body form which has enabled them to colonise every major habitat and master every known feeding type. Morphologically they resemble flatworms (Platyhelminthes) with the addition of the tongue-like radula and a dorsal shell. The radula is mounted on the odontophore which is everted through the mouth via protractor muscles, in the process erecting the "teeth" which rasp the substrate. The shell is laid down in distinct layers and a consequence of this has been the development of an almost conical body form. The shell is secreted by the mantle and extends down over the uncovered regions of the body, able to pull the body into the shell for protective purposes. The breathing apparatus are gill-like in form and are located in the mantle cavity, each gill being composed of a longitudinal axis from which branch flat filaments, each of which is supported by a tiny chitinous rod. In aquatic species cilia on the gills drive water between the filaments through which blood diffuses in counter-current.
FAUNA Paraguay deals with two Classes of Mollusc (the other classes are all marine). These two classes make up 98% of all known living molluscs and are the only ones to have successfully colonised terrestrial and freshwater habitats. Click on the links below to access the species galleries and class introductions:
Class Bivalvia - Including the freshwater bivalves (mussels etc).
Class Gastropoda - Including the Snails and slugs.
Designed by Paul Smith 2006. This website is copyrighted by law. Material contained herewith may not be used without the prior written permission of FAUNA Paraguay. Photographs on this web-site were taken by Paul Smith, Hemme Batjes, Regis Nossent, Alberto Esquivel and Hugo del Castillo and are used with their permission.
