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C@LENTERATA. 
1, Metazoa with radial (axial) symmetry. 
z. Body of two layers of cells, ectoderm and endoderm, enclosing one continuous 
gastric cavity, which communicates to exterior by one opening, the mouth- 
anus.* 
An pw 
formation). 
Class I.—Hyprozoa. 
Types—Hydra; Obelia; 
(Tubularia). 
1. Simple gastric cavity. 
2. No ectodermal gullet. 
3. Two phases, a free- 
swimming medusoid 
and sedentary hy- 
droid. 
MEDUSOID. 
A velum. 
Gonads ectodermal, 
Four radial canals. 
Simple sense-organs. 
Nerve-rings. 
HYDROID. 
t When colonial, 
usually has horny 
perisarc. 
2. Skeleton has no 
septa. 
Class II.—Scypnozoa. 
Types—Actinia; Alcyon- 
tum; Aurelia; 
(Madrepora). 
. Gastric cavity divided 
by mesenteries into 
central and peripher- 
al cavities, 
2. An ectodermal gullet. 
3. Two phases, a_free- 
swimming medusoid 
and sedentary hy- 
droid. 
MEDUSOID. 
No velum. 
Gonads endodermal. 
Many radial canals. 
Tentacles modified in- 
to complex sense- 
__organs. 
Diffuse nerve fibres. 
HYDROID. 
1. Whencolonial, has 
calcareous skele- 
ton. 
2, Skeleton has septa. 
PHYLUM CC@ELENTERATA, 
. A structureless lamella, the mesogloea, between the two layers. 
. Ectoderm cells bear nematocysts. 
» Asexual reproduction by budding produces colonies. 
. Aquatic and mostly marine, free-swimming, and sedentary (tending to coral 
Class II1—CTENopPHoRA. 
Types—Cydippe ; (Berot). 
1. Gastric cavity consist- 
ing of stomach and 
gastro vascular 
canals. 
2. An ectodermal gullet. 
3. One phase only, a free- 
swimming, modified 
from medusoid type. 
4. Eight longitudinal 
rows of cilia. 
. Nematocysts rare, 
. Single aboral  sense- 
organ. 
an 
* Usually termed the ‘‘ mouth.” 
