Ctenophores are exclusively marine, solitary, free swimming or pelagic, very active animals with transparent and flat or oval body shape and have following important characters : 

1.    Body soft, delicate, transparent and gelatinous without segmentation. 

2.    Polyp phase is absent in their life cycle, shape is typically spherical, pear shaped or cylindrical, flat in some. 

3.    They are radially symmetrical, diploblastic, tissue level of organisation and devoid of cnidoblast cells. 

4.    Tentacles may be present or absent. When present, the number of tentacles is 2. They are solid and possess adhesive cells called colloblasts (lasso cells). Digestion is both extracellular and intracellular. Bioluminescence (the property of a living organism to emit light) is well-marked in ctenophores. 

5.    The animals move by cilia, which join together to form comb plates. There are eight median combplates forming locomotor organs, hence organisms are called comb-jellies or sea-walnuts. 

6.    Gastrovascular cavity is branched and opens to the exterior by stomodaeum. 

7.    They are diploblastic animals but the mesoglea is different from that of cnidaria; it contains amoebocytes and smooth muscle cells and is comparable to a loose layer of cells. From this viewpoint, ctenophores may be considered as triploblastic. 

8.    Skeletal, circulatory, respiratory and excretory systems are absent. Nervous system is diffuse type. 

9.    The presence of a special sense organ 'Statocyst' at the opposite end of the mouth (aboral end) is the characteristic of the members of this phylum. 

10.    All are hermaphrodite. Testes and ovary formed side by side from endoderm of digestive canals. 

11.    Asexual reproduction doesn't occur. They reproduce only by sexual means. Fertilization is external. Development is indirect and an immature ciliated stage called 'cydippid larva' is found in some forms. 
Examples: Hormiphora (The sea walnut), Pleurobrachia (The sea gooseberry), Ctenoplana, Cestum (The venus girdle) 

Concept Builder

Word roots and Origins : 
(a)    Colloblasts from the Greek kolla meaning "glue" and blastos meaning "bud". 

(b)    Ctenophore from the Greek ktene meaning "comb" and phors meaning "bearing".