BRANCHIOSTOMA-RENAL PAPILLAE

The cells are present on the floor of atrial cavity form renal papillae which are probably also excretory in function.

BRANCHIOSTOMA-EXCRETORY SYSTEM

They closely resemble the protonephridia of flatworm providing good example ofparallei evolution. Some other organs and cells are also shows excretory systems.

BRANCHIOSTOMA-LYMPHATIC SYSTEM

Lymph as such is lacking.The so-called lymphatic spaces or sinuses present inside fins and metapleural folds, are called filled with colourless blood lacking in leucocytes. It is the oxygen required by the animal is obtained by the gaseous exchange between outside water and blood inside these superficial sinuses.

BRANCHIOSTOMA-COURSE OF CIRCULATION

Blood flows anteriorly inside parietal ,subintestinal and posterior cardinal veins and ventral aorta. It flows posteriorly inside lateral and median dorsal aortae and anterior cordinal vein. The course of circulation can be graphically represented .

BRANCHIOSTOMA-PARIETAL VEINS

Bloodfrom dorsal body wall is collected by a pair of parietal veins one on either side. They run above the intestine for some distance and the turn ventrally to join the sinus venous.

BRANCHIOSTOMA-CARDINAL VEINS

The blood from ventrolateral region is collected on either side by an anterior and a posterior cardinal vein. The two unite just behind the pharynx to form a common cardinal vein or ductus cuvieri. The two ductus curieri then run down through the atrium to join the sinus venosus.

BRANCHIOSTOMA-HEPATIC PORTAL SYSTEM

The subintestinal vein continue anteriorly as the hepatic portal vein running ventrally along up in the midgut diverticulum into which it breaks up in a capillary network. Blood is collected by a hepatic vein running along its dorsal border and bending downwards to join the sinus venosus. Hepatic portal system occuring for the first time in Branchiostoma is a precursor of that of higher chordates.

BRANCHIOSTOMA-SUB-INTESTINAL

The blood from tail region is collected by a mid-ventral caudal vein and from intestine by lateral intestinal veins. These join a small median longitudinal subintestinal vein lying below the intestine in the form of a plexus. Blood flows in it anteriorly.

BRANCHIOSTOMA-VENTRAL AORTA

It is a large median longitudinal artery extending forward from sinus venosus. It is mid-ventrally in the wall of pharynx below the endostyle in the subendostylar coelom, also called as subendostylar aorta. Blood flows in it anteriorlydue to rhythmic contractions of its muscular walls. The ventral aorta gives off a series of a paired lateral afferent branchial arteries . The afferent vessels leave the pharynx the pharynx dorsally as in the form of efferent branchial vessels which opens into a lateral dorsal aorta of that sac. The vessels splits into a small capillary network the nephric glomerular sinus or glomus in relation with a nephridium.

BRANCHIOSTOMA-SINUS VENOSUS

It is small, thin-walled sac present below the posterior end of pharynx . Blood from different parts of the body is collected by sinus venosus through a number of veins and pumped forward into the ventral aorta.

BRANCHIOSTOMA-BLOOD VASCULAR SYSTEM

Branchiostoma is closed type blood vascular system. Blood is colourless due to lack of any respiratorypigment and corpuscles. Blood vessels in some lymph spaces such as in metapleural folds and the dorsal and ventral fins. Its main tobe the transportation of food and excretory products rather than oxygen and carbon-di-oxide for gaseous exchance.There is no structural differences between arteries and veins due to their homologies with blood vessels of higher chordates.

BRANCHIOSTOMA-RESPIRATORY MECHANISM

The pharyngeal wall of branchiostoma is richly vascular and the warer current entering the pharyngeal cavity brings fresh oxygen. The blood flows so close to the surface that some exchange between carbon-di-oxideof blood and oxygen of water can easily occur. There is no capillary network in gill bars. The blood lacks a respiratory pigment. Many workers questions about the respiratiory role of pharynx. It is probable that most gaseous exchange occurs through superficial areas such as fins, metapleural folds and atrial wall containing lymph spaces.

BRANCHIOSTOMA-DIGESTION

.Digestive enzymes are secreated from two source ,midgut diverticulum and the midgut epithelium. The food cord from pharynx passes through oesophagus into midgut. Digestion starts in the midgut by ciliary action. In the ilio-colic ring, the food cord undergoes rotation due to ciliary activity. This breaks up the food material into still smaller particles, throughly mixes up enzymes with food and delays the backwards passage of food to allow more time for action of enzymes.Digestion is mainly extracellular but intracellular digestion also takes placewhich is unique as it isunknown in other vertevrates. Intracellular digestion takes place mainly in thephagocytic cells of midgut diverticulum. Some food particles may pass into atrial cavityand eventually engulfed by the phagocytic cells present in renal papillae on the floor of atrial cavity.

BRANCHIOSTOMA-FEEDING MECHANISM

Branchiostoma is a ciliary or filter feeder, like an ascidian. The animal leads a sedentary life buried in sand .Food particles are filtered from the current of water entering pharynx through mouth and finally going out through atriopore.The atriopore closes and the transverses muscles oc the floor undergo sudden contraction. This sets up a reversal of water current or rejection current ejecting out forcefully through through the enterostome and mouth. Pharynx plays the most important part in food collection. In side pharynx the food particles get entrapped in mucus secreted by the glandular tracts of endostyle and by pharyngeal epithelium. The endostylar cilia and the frontal cilia of gill bars beat upwards so that mucous sheets laden with food particles move dorsally to the epipharyngeal groove. The cilia of epipharyngeal grrove beat backwards moving the food-laden mucus into the oesophagus in the form of a narrow food cord.

branchiostoma-physiology of digestive system

FOOD-Branchiostoma is a microphagus animal feeding on diatoms,desmids,protozoans and pelagic microscopic organisms, in sea water.

BRANCHIOSTOMA-DIGESTIVE GLANDS

The midgut diverticulum reffered to as''liver''s the main digestive gland.It  arises as  a blind pouch from the ventral oesophagus and midgut. It is surrounded by a narrow coelomic cavity. Its inner lining has a strong ciliated groove for movements of food. Its zymogen cells secrete a number of digestive engymes. The epithelial lining of intestine also contains glands cells that secrete digestive enzymes.

BRANCHIOSTOMA-ANUS

It is a small circular aperture controlined by a sphinter.It opens at the base of caudal fin a little on the left side of the mid-ventral line.