EXCRETORY SYSTEM
Excretory organs consist of glandular renal growths or renalappendages that are wrapped around the paired precava and extract nitrogenous wastes from the blood and pour it into a pair of viscero-pericardial sacs. One end of these sacs opens into the pericardialcavity and drains its contents, while the other end opens into the mantle cavity as external renal opening. Pancreaticappendage also performs excretory function. The excretory material from this is collected by the single mid-dorsal sac that opens into the two viscero-pericardial sacs. The excreted nitrogenous wastes are in the form of guanin.
NERVOUS SYSTEM
Nervous system is advanced type and centralised. There is a brain enclosed within a cartilaginous skull. It is formed by the fusion of cerebral, pedal and pleuro-visceral ganglia. On the anterior side of brain there is a basalbrachialganglion from which emerge 10 brachial nerves that on the anterior side meet 10 brachial ganglia in a nerve ring. From this brachial ring nerves go to tentacles and oral arms. Visceral nerves emerge from the ventral side of the brain.
From the posterior side of brain a pair of pallialnerves emerges and meets the large stellateganglia on the lateral sides. From the stellate ganglia nerves are supplied to the visceral organs and the fins. From the posterior end of the brain also emerge a pair of branchial nerves that innervate the two gills or ctenidia.
Sympathetic nervous system includes a pair of nerves emerging from brain and joining the gastric ganglion in the stomach lining.
SENSE ORGANS
Sense organs include a pair of large eyes, a pair of statocysts situated on the ventral side to the pleuo-visceral ganglion of brain, a pair of olfactorypits behind the eyes and gustatoryorgan on the floor of the buccal cavity.
Cephalopod eye is strikingly similar to the vertebrate eye, although the two are not homologous structures. Cornea is not true cornea as it is made of modified horny skin. Sclera is made of cartilages that form eye orbit. Choroid is absent. Ciliary body is present and holds the lens in its place. Retina contains rod cells only but does not have fovea centralis. Unlike in vertebrates, the rod cells point towards the source of light and the nerve fibre is attached to the posterior side of rod cells. The gelatinous vitreous humour fills the eye ball posterior to the lens. A pair of whitish optic glands is present at the junction of the optic nerve with the eye ball. There is no blind spot in the eye of cephalopods.
REPRODUCTIVE SYSTEM
Sexes are separate. Male has a single yellowish testis enclosed in the coelomic capsule, which is located on the posterior end of the visceral cavity. Vasdeferens emerging from the testis is a highly coiled duct that leads to an elongated and ciliated seminalvesicle. An accessory prostategland is attached to the terminal end of the seminal vesicle. Seminal vesicle opens into a large Needham’ssac that serves to store spermatophores till they are passed out through the male genital opening at the base of the funnel. Sperms are produced in testis but they are packed in elongated and chitinous spermatophores inside the seminal vesicle. These spermatophores possess a spring apparatus at the base of the cap that makes them blow up to release sperms when placed inside the mantle cavity of female.
Female has a single whitish saccular ovary enclosed in a coelomic sac and located on the posterior end of the visceral cavity. Ova travel through the oviduct and are released in bursacopulatrix, which is formed by the enlargement of the funnel and in which fertilization takes place. A pair of nidamentalglands secrete egg capsule around the fertilized eggs. The orange coloured accessorynidamentalglands secrete sticky material that helps the eggs to adhere to the sea weeds where the female deposits them.
Conventional copulation does not take place in Sepia. Sperms are packed in spermatophores which are released into the mantle cavity from where male collects them with its hectocotylized arm and transfers into the mantle cavity of female. Left 4th arm is modified as hectocotylised arm in Sepia for the transfer of sperms.
Development is direct and there is no larval stage in cephalopods.