The space between body wall and alimentary canal is called as
coelom or body cavity.
It remains lined on both side by coelomic epithelium derived
from mesoderm so it is true coelom or schizocoel. The coelom is not continuous
and remains differentiated into a number of small chambers called as coelomic
chambers by plate like structures called as septa. Each septum arises from
inner region of inter segmental groove of body wall and extends up to wall of
alimentary canal. Each septum consists of interwoven muscle fibers covered on
both side by coelomic epithelium. The first septum lies between fourth and
fifth segment and is thin and membranous. Next five septa are thick and
muscular. These septa lie obliquely in between body wall and alimentary canal
while
other septa lie horizontally. In between 8th to 10th segment only one septum is present. Anterior nine septa are without perforations while others are perforated through which coelomic fluid passes from one chamber to another.
other septa lie horizontally. In between 8th to 10th segment only one septum is present. Anterior nine septa are without perforations while others are perforated through which coelomic fluid passes from one chamber to another.
Coelomic fluid: The coelom remains filled with a type of fluid called as coelomic fluid which is alkaline , watery or milky with water, protein, salts and four types of cells.
The cells are Amoebocytes or Phagocytes or Granulocytes, Mucocytes, Circular nucleated cells and chloragogen cells. The Phagocytes engulf micro-organisms. The chloragogen cells help in excretion.
Functions of coelomic fluid:
·
It
acts as hydraulic skeleton.
·
It
helps in internal transport.
·
It
comes out through dorsal pores and makes body surface moist.
·
It
helps in plastering the burrows.
·
The
Phagocytes engulf micro-organisms.
·
The
chloragogen cells help in excretion.