290 Animal Biology 



A stomodaeum (gullet) is present in certain species and absent in others. All 

 scyphozoa are carnivorous and marine. They are usually free floating, although 

 at times they may be sedentary. Sizes range from one inch to four feet in diam- 

 eter. They have a very inconspicuous hydroid stage in their life cycle. The 

 medusa stage is large and without a velum. The medusa of the scyphozoa can 

 be distinguished by notches (usually eight) in the margin of the umbrella. 

 Examples: larger jellyfishes such as Aurelia (Fig. 94). 



Fig. 94. — Diagram of the life history of the jellyfish {Aurelia aurita) of the 

 phylum Coelenterata, class Scyphozoa. 1 , Adult jellyfish (medusa) ; T, tentaculo- 

 cyst (for equilibrium) ; F, gastric filaments (with nematocysts) ; O, oral arm; 

 M, mouth; P, gastric pouch; 2, egg; 3, sperm (from another adult) ; 4, zygote 

 (fertilized e.gg) ; 5, planula (ciliated larva) ; 6, 7, stages in the development of 

 the scyphistoma; 8-10, stages in the development of the strobila; 11, ephyra (im- 

 mature medusa). (From White: General Biology, The C. V. Mosby Company.) 



Class 3 — Anthozoa (antho-zo'a) (Or. anthos, flower; zoon, animal). — The 

 hydroid polyps have a well-developed stomodaeum (gullet) which is fastened to 

 the body wall by a number of radially arranged membranous mesenteries. Most 

 of the polyps produce a colony by budding, although a few are solitary. This 

 colonial organization gives the efTect of a flower; hence, the name Anthozoa. 

 Several species secrete a calcareous skeleton known as coral. There is no medusa 

 stage in the life cycle. 



Examples: Sea anemone (Metridium) (Fig. 95) and most of the stony corals, 

 sea pens, sea fans, precious corals (Fig. 96). 



