126 CCELENTERATA 



large and extensively branched and in the Rhizostomata the mouth is 

 closed by the coalescence of its sides, small pores remaining through 

 which nutriment is taken in. The gastrovascular space is complex in 

 form and usually consists of four radial pouches forming a large space 

 in the center of the animal and additional radial canals which often 

 branch and may be joined at their outer ends by a circular canal. 



The gonads are four in number and often brightly colored; they 

 are specialized portions of the entoderm and appear in the interradii of 

 the gastrovascular space. In many species four large pockets, called the 

 subgenital pockets (Fig. 216, S) and probably respiratory in function, 

 are present in the subumbrella directly beneath the four gonads. Beside 

 each gonad are usually a number of cylindrical mesenterial filaments, 

 armed with nettle organs. 



The finer structure of the Scyphozoa is essentially like that of the 

 Hydrozoa. The mesoglea is different, however, in that it is much firmer 

 and usually cellular. The sense organs are also different, being perhaps 

 modified tentacles, and are called tentaculocysts or rhopalia. 



The Scyphozoa are all marine and among the most familiar animals 

 along our shores. The class contains 5 orders and about 180 species. 



Key to the orders of Scyphozoa: 



a t Body stalked and sessile, there being no medusa stage .... 1. STAUBOMEDUSAE 

 Oj Free-swimming medusae present. 



&! Medusa with distinct constriction about its middle 2. COEONATAE 



& 2 No such constriction present. 



G! Tentacles present either on the margin or the subumbrella. 

 di Medusa cuboidal in shape with 4 long marginal tentacles or groups of 



them 3. CUBOMEDUSAE 



d a Medusa with 8 or more tentacles on margin or subumbrella. 



4. SEM^EOSTOMEAE 

 c 2 No tentacles on margin or subumbrella 5. RHIZOSTOMAE 



ORDER 1. STAUROMEDUSAE. 



Body conical in shape with aboral surface usually drawn out to 

 form a stalk by which it is temporarily attached, representing a sexual 

 scyphistoma ; margin with 8 prominent lobes, each with a cluster of short 

 knobbed tentacles; without sensory organs but often with marginal 

 adhesive pads (marginal anchors) in the angles between the lobes: 25 

 species and 2 families, the animals usually attached to seaweed in 

 shallow water. 



FAMILY LUCERNAEIIDAE.* 



Margin with 8 lobes, each with numerous knobbed tentacles; animal 

 attaches itself temporarily to algae, along which it crawls : 5 genera. 



* See "Lucernariae and Their Allies," etc., by H. 3. Clark, Smithsonian Contrib. 

 to Knowledge, Vol. 23, 1878. 



