Physiology of Finfish and Shellfish (2+1)

2.1.38. Respiratory physiology of bivalve

 Gill type

Description

Protobranch

This Gill structure tends to occur in primitive groups and appears as a small leaf like structure.

Filibranch

This gill structure consists of individual filaments forming ‘W’-shaped structures that come together to form lamellar sheets.

Eulamellibranch

These form ‘W’ – shaped gills with cross-partitions joining the filaments to create water – filled cavities in between them.

SEptibranch

These gills are only found in poromyacea, a super family of the rock borers. They run transversely across the mantle cavity, endosing the inner chamber with only a small connection to the occur outer cavity.

Most bivalves have only one pair of gills, or even only one gill. Generally the gills are rather like feathers in shape, although some species have gills with filament on only one side.

The division of the mantle cavity facilities enter of water near the bottom and exits near the top. Their filaments have three kinds of cilia, one of which drives the water current through the mantle cavity, while the other two help to keep the gills clear. If the osphradia detect noxious chemicals or possibly sediment entering the mantle cavity, the gills cilia may stop beating until the unwelcome intrusions have ceased. Each gill has an incoming blood vessel connected to the hemocoel and an outgoing one to the heart.

The gills consist of four crescent shaped plates, two half gills on each side which hang down from the roof of the mantle cavity. Like book leaves, They represent a series of ciliated sieves, providing an efficient feeding surface. Two rows of long delicate branchial filaments are inserted at right angles along the whole length of the axis or vascular base which extends from the ventral border of the palpsanteriorly curving round ventrally and posteriorly to a point opposite the anus. Its convexity extends first forwards and then downwards. Where they terminate, the mantle lobes of the sides are slightly united by the inner mantle of olds thus dividing the mantle cavity into a large inhalant chamber containing the gills and much smaller exhalent chamber water enters by one and leaves by the other.

The common base of each ctenidium is a vascular ridge reaching from the anterior end of the gills. Hollow out growths, the inter – lamellar junctions, containing branches from the afferent vessels, convey blood from the axial trunk to the base of reflected lamellae. The blood enters the individual filament flow outwards to the free margin, passing over to the direct filaments, returning inward to the branchial or ctenidial axis, where it joins the efferent vessel by openings along each side. The filaments are joined by chiefly by the inter-locking sliff cilia of the large ciliated discs which occur at intervals throughout their length. The normal function of the ordinary cilia on the branchiae is to create a current of water which enters the pallial chamber and passel over and through the branchial lamellae. They serve to purify the blood flowing in the filaments and to convey the food particle to the mouth.