The body wall of a common sponge consists of three
lavers which are
(i) Pinacoderm (dermal layer) It is an outer cellular
layer which consists of
(a) flattened pinacocytes
(b) oval porocytes
(ii) Choanoderm (gastral layer) It is inner cellular layer
consisting of highly specialised flagellated cells called
choanocytes or collar cells.
(iii) Mesoglial layer (mesenchyme) It is a non-cellular
layer found in between pinacoderm and choanoderm.
It has fine dispersed spongin fibres and numerous
spicules It also contains amoebocytes of both
pinacoderm and choanoderm.
Amoebocytes are modified into following cells
(a) Archaeocvtes (totipotent cells)
(b) Trophocytes (nurse cells)
(c) Thesocytes
(d) Gland cells
(e) Collencytes
(f) Myocytes
(g) Germ cells
(h) Chromocytes
(i) Phagocytes.