MARINE AQUARIA 
Hatrsarca, having a gelatinous or fleshy substance forming an ir- 
regular crust on the object to which it adheres. 
HaticHonpriA, having an elastic body permeated by canals opening 
to the surface and siliceous spicula in the fibre distributed throughout its 
homologous body. 
Sponct4, having a very porous body composed of net-fibres traversed 
by canals opening to the surface, the fibres without spicula. Very irregu- 
lar and variable in form, and parasitical or incrusted on and under stones 
and other objects. 
Sponges should not be introduced into smaller aquaria and should 
be carefully scraped from stones and other objects, as they soon decay and 
may pollute the water. 
C@LENTERATAOR Potyps. Theseare somewhat higher forms ofanimals. 
The Hydrozoa are zodphytes resembling seaweeds, which live in colonies, 
small compound jellyfishes composed of many individuals; and the Mil- 
lepores live in colonies and secrete a stony instead of horny skeleton. 
Of these no further mention need be made. The Scyphozoa are larger 
jellyfishes of various forms of development, but also do not require men- 
tion. The Actinozoa include anemones, actinia and actinoid corals, of 
which the first are of particular interest, but other forms of Corals, Cor- 
allines, Sea-pens, Sea-whips and Sea-fans, and the Ctenophora, including 
the Comb-jellies, require but brief mention, as none of them will survive 
in the Marine aquarium. 
SeA Anemones and Actinia. These polyps belong to the order 
Actinaria. They mostly inhabit crevices, dark holes and under stones, 
but some hardy species may be taken in exposed positions, or piles, sub- 
merged woodwork and other firm objects. There are both deep and 
shallow-water forms. They generally consist of an undivided column or 
stalk with a pedal disc or holdfast at the under side, and an oral disc with 
central mouth surrounded by circles of tentacles at the upper. ‘They are 
capricious in the forms which they assume and when fully expanded are 
often of considerable size, but are sensitive and when disturbed collapse 
and shrink into inconspicuous dusky buttons, as they are soft and very 
contractile. The most of the Actinaria are developed from eggs which 
form on the edges of the inner walls of the column. These, when ma- 
ture, are ejected from the mouth, small ciliated spheres which swim about 
until they find a suitable location to which to attach themselves. Some 
forms reproduce by budding, either on the disc or from the sides of the 
column. As a means of defense they emit long slender threads or 
acontia, having minute stinging cells. Nearly all are carnivorous and feed 
on small animal organisms, crustaceans and molluscs. 
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