Question

In sponges, nutrition, respiration and excretion depends upon
A. Circulatory system
B. Ambulacral system
C. Haemocoelomic system
D. Canal system

Answer 1

Sponges are primitive multicellular acoelomate animals and have cellular level of organization. There is no complexity in the organization of the members of this phylum.

Complete answer:
Sponges have various body forms and shapes with irregular shape mostly Asymmetrical. (Radial symmetry in Sycon and Leucosolenia)
Body wall consists of -
(i) Outer Pinacoderm
Consists of:
(a) Pinacocytes (Flat cells)
(b) Porocytes (oval cells)
(ii) Inner Choanoderm :
Consists of flagellated collar cells or choanocytes (Unique Characteristic of Porifera)
(iii) Between these two layers a gelatinous material Mesenchyme is present which contains certain
Amoebocytes cells like:
Scleroblasts : For formation of skeleton elements.
Archaeocytes : Totipotent cells for the formation of gametes.

Body wall encloses a large central cavity, the spongocoel or paragastric cavity with small hollow canals.
Canal system or water transport system : in the sponges, water enters through ostia into spongocoel and comes out through osculum. This pathway of water transport is helpful in food gathering (Nutrition), respiratory exchange and removal of Wastes (excretion).
It is a unique feature of sponges.

So, the correct option is (D) Canal system.

Additional Information:
Choanocytes lines(surrounds from inner side) Spongocoel cavity and the canals.
Nutrition is holozoic with intracellular digestion.
Skeleton is internal, consisting of tiny calcareous spicules or siliceous spicules or fine spongin fibre located in mesenchyme. Scleroblast secretes spicules and spongioblast secretes spongin fibres.
Excretion & Respiration takes place by diffusion of gases through the general body surface. Excretory matter is Ammonia.
Reproduction takes place by means of :-
(A) Asexual - By Budding or Fragmentation or by Special cell mass Gemmules
containing Archaeocytes.
Endogenous buds of asexual reproduction in sponge are known as Gemmules (In unfavorable condition)
(B) Sexual - Sponges are Hermaphrodite, fertilization is internal and cross due to Protogynous condition and development is indirect having a larval stage which is morphologically distinct from adults.

Note: Water canal system is the unique character of phylum Porifera.
Water vascular system is the unique character of the phylum Echinodermata.