2 COELENTERATA [ CH - 



Phylum COELENTERATA. 

 The classification of the Coelenterata is as follows : 



Class I. HYDROZOA. 



Coelenterata without mesenteries or gullet lined by ectoderm : 

 genital cells derived from ectoderm. 

 Order 1. Hydrida. 



Only hydroid persons present, not permanently attached 

 .but capable of locomotion: the buds become free. 

 Order 2. Hydromedusae. 



Composite fixed colonies of hydroid persons from which 

 medusoid persons are budded o|f. 



Sub-order (1). Gymnoblastea (Anthomedusae). Perisarc 

 confined to the base of the hydroids : medusoids have eyes and 

 bear gonads on the manubrium. Ex. Bougainvillea, Tubutaria. 

 Sub-order (2). Calyptoblastea (Leptomedusae). Perisarc 

 expanded to form cups called hydrothecae, into which the heads 

 of hydroid persons can be retracted : medusoids have ears and 

 bear gonads on the under side of umbrella. Ex. Obelia. 



Sub-order (3). Hydrocorallinae. Perisarc thick and 

 calcareous, surrounding chiefly the stolons which are given off at 

 various levels and form a thick mass. Hydroid persons of two 

 kinds nutritive and tactile. These are closely allied to the Gymno- 

 blastea of which they ought to form a sub-division. Ex. Millipora. 



Sub-order (4). Narcomedusae. The hydroid is fixed to 

 the inside of the bell of another Medusa. The manubrium of 

 the Medusa is poorly developed, and the wide stomach occupies 

 the under side of the bell. The sense-organs are reduced 

 tentacles projecting at the edge of the bell. 



Sub-order (5). Tr achy medusae. Forms in which the 

 hydroid does not bud but develops directly into a Medusa in 

 which there is a long manubrium traversed by the radial canals, 

 the lower portion of which contains the stomach. The sense- 

 organs are reduced sense-tentacles enclosed in sacs of ectoderm. 



Sub-order (6). Siphonophora. Free-swimming colonies 

 consisting of hydroid and medusoid persons in which the base 

 is modified into a float or some of the medusoids are trans- 

 formed into swimming organs, or both arrangements are 

 combined. 



