In this article we will discuss about the dissection of Unio. Also learn about: 1. General Anatomy of Unio 2. Dissection of Nervous System of Unio.
General Anatomy of Unio:
Hold the animal in your left hand with broad anterior end on the left side. With a scalpel scrap the shell margins. Now insert he scaloel blade between two valves through the anaI aperture situated on narrow posterior end and try to detach the anterior and posterior adductor muscles from the upper valve which connect the body with it.
As, soon as you feel that the anterior and posterior adductor muscles are detached try to raise the upper valve slowly and with pressure by rotating the scalpel Remove the upper (left) valve as soon as it opens. Now remove the left mantle flap which covers the whole body.
As soon as you remove the mantle you will notice the anterior and post adductor muscles, and tiny retractor muscle close to the adductors. Just below the anterior adductor lies the thin strap-like protractor muscle. At the posterior narrow end lies the inhalent and exhalent siphons with fringed edges.
Just below the adductor and protractor muscles lie a pair of labial palps and below them lies the large hatchet shaped foot differentiated into a dorsal soft and bulging portion and a ventral hard, solid and edged portion for burrowing into sand and crawling on substratum.
Above the foot, just behind labial palps, lies the hat gill with distinct outer and inner laminae Just above the gills, in between the two adductor muscles, lies the visceral mass H you )us remove the membrane from above the visceral mass you will locate the heart surrounded by pericardium.
Dissection of Unio:
To locate the digestive organs remove the skin from the soft bulging portion of foot. Inside you can locate coiled intestine, gonad between the coils of intestine and stomach just above the labial palps behind the anterior adductor muscles.
Dissection of Nervous System of Unio:
After removing the left valve and cutting the left mantle flap proceed to trace the nervous system. First of all locate the cerebro pleural ganglion at the base of anterior protractor muscle close to the point the labial palps are attached. This is a small creamish or yellowish mass.
Now locate an “X” shaped visceral ganglion situated in middle of anterior surface of post-adductor muscle. After locating these two ganglia cut the gill laminae at the base and trace the cerebrovisceral connective through visceral mass from visceral ganglion towards cerebral ganglion.
Now proceed to locate pedal ganglion. It is a dark yellowish, paired, spindle shaped mass situated inside the soft and bulging portion of the foot. To locate this cut the solid hard portion of foot from the line it joins the soft bulging portion.
Now divide the cut surface of soft bulging portion into three approximately equal portions. Around the point where anterior 1/3 meets the posterior 2/3 try to locate the pedal ganglion after stretching the two sides of soft visceral portion of foot apart.
Now, trace the cerebropedal connectives from pedal to cerebro-plural ganglion. In the end trace the cerebral commissure which runs around the mouth from one cerebropleural ganglion to the same ganglion of the other side.
Black paper your dissection by inserting small triangular pieces of black paper below the connectives and commissures.
