CCELENTERATA — CTENOPHORA 139 



CLASS D, CTENOPHORA (COMB-JELLIES) 



Pelagic individuals with no sessile or colonial stage. Tenta- 

 cles when present are usually two in number. Movement 

 is by the large cilia which are fused into comb-like structures ; 

 these are arranged in 8 meridian-like rows or swimming plates. 

 Not known in the fossil state. Example : Cestus (Venus' 

 girdle). 



Derivation of name. — Ctenophora > Greek kteis, a comb, 

 + phoros, bearing, from the fusion of the large cilia to form 

 comb-like swimming structures. 



1. In what respects are the Coelenterates an advance upon 

 the sponges ? 



2. Define the four classes into which the Coelenterata are 

 divided, with a living and a fossil (where possible) example of 

 each. 



3. Since the large jelly-fish, the Scyphozoa, consist of about 

 99 per cent water, how have fossil records of them been made ? 



4. Distinguish Hydrozoa from Anthozoa, in (a) the soft body, 

 {h) the hard skeleton. 



