Lecture 321 of 373: Unio or Lamellidens or Anodonta: Freshwater Mussel (22 mins) | CUET (Common University Entrance Test) PG Zoology (SCQP28) | Complete Video Course 373 Lectures [222 hrs : 42 mins]

Details

Unio is a common freshwater mussel found in freshwater lakes, rivers and streams. It belongs to class Bivalvia and Pelecypoda.

In a buried position, the posterior tip of its shell remains exposed in water to facilitate entry and exit of water for respiration and feeding.

It crawls slowly with the help of plough like, wedge- shaped muscular foot that leaves a deep trail.

Food consists of microscopic organisms, both animals and plants, which are fed upon by filter feeding mechanism involving both ciliary as well as mucoid movements.

Sensitive to light, tough and other stimulus by withdrawing its foot and closing the siphons meant for incoming and outgoing water currents.

Soft bodied animal is completely inside the shell, representing the exoskeleton. Shell consists of two similar, more or less oval, convex valves that are joined at their dorsal margin or hinge line by a strong hinge ligament. Shells are equivalve (similar in shape and size). On the anterior surface, a raised part, called Umbo is present, represents the oldest part of the shell.

Shell valves are attached to the mantle of the body with three anterior and two posterior sets of muscles.

Two blade-like processes, the hinge teeth, one near the umbo and other along the hinge line, hold the valves from slipping out of positions.

When a foreign particle falls in between the shell and mantle, the mantle is stimulated to secrete concentric layers of nacre around it, resulting into pearl formation. although the pearl of Unio is not commercially precious.

Mantle consists of two fleshy lobes which are dorsally attached to the body and ventrally to the shell valves. Exhalent siphon is present dorsally and inhalant siphon is present ventrally.

Mantle cavity has visceral hump which contains alimentary canal, gonad, digestive glands, pericardial cavity, heart, blood vessels, kidneys and bladders; foot, labial palps, mouth and gills.