DISSECTION OF SEPIA (CUTTLE FISH)
External features of Sepia (Cuttle Fish)
Sepia is commonly found in sea in India. Very favourite class room specimen and very good animal tc study the nervous system. The preserved specimen is brownish in colour bluish with leathery texture. The animal can atonce be recognized by the tentacles, majestic eyes and continuous lateral fin over the viscera hump or trunk. Head and trunk are joined by a narrow neck. The body is divided into head, neck and trunk. For detailed characters see under chapter Museum Specimen.
Nervous system of Sepia (Cuttle Fish) Procedure
For dissection of sepia take a nicely preserved good specimen. It is always better to check the specimens. Pindown the animal with dorsal side upwards. Starting from the posterior end make a longitudinal incision upto cephalic end. Pin The lateral flaps of the body carefully by cutting the skin and muscles. First expose the cerebral ganglion in the head. Also expose visceral ganglia and pedal ganglionic mass. These stellate ganglion on mid lateral regions. After exposing these two ganglia proceed to trace the following nerves from anterior to posterior regions. If asked then black paper your dissection of sepia to show the nervous system.
Anterior nerves (From the cerebral ganglia or brain)
- A pair of optic nerves: These nerves arise from the anterolateral portion of the cerebral ganglia on each side and after making in optic ganglia, they innervate retinal cells by the final retinal nerves.
- A pair of tentacular nerves : Originate from the pedal ganglionic mass just below the cerebral ganglia. They innervate tentacles.
- Eight brachial nerves : The brachial nerves also originate from the pedal ganglionic mass and they innervate the oral arms. The brachial nerves after running for a short distance from a interbranchial commissure.
- Other nerves and ganglia seen are olfactory ganglion, inferior anterior ophthalmic nerve, inferior posterior ophthalmic nerve.
Posterior nerves (From cerebral ganglia into trunk)
- A pair of pallial nerves: They originate from the postero-lateral position of the cerebral ganglia. They run obliquely in the posterior direction on each side and make a thick rounded stellate ganglia. Several outer branches from the stellate ganglia innervate mantle and various inner branches innervate the fin.
- A pair of sympathetic nerves : They originate from the mid posterior region of the brain, run posteriorly and form gastric ganglion. Fine nerves from gastric ganglion innervate liver, stomach, intestine and caecum, etc.
- A pair of visceral nerves : They originate from the posterior edge of visceral ganglia and run posteriorly. For sometime they run together, then separate and form a posterior visceral commissure. A pair of brachial nerves arise from the posterior visceral commissure and innervate gills. Various fine nerves arising from posterior visceral commissure innervate various visceral organs like cardiac nerves, etc.