ZOOLOGICAL 
740 
TUBULIPORA ATLANTICA AND OVICELL, ENLARGED 
From a drawing by Mr. H. J. Shannon 
BRYOZOA OR MOSS-ANIMALS. 
HE Bryozoa or moss-animals, so named 
from the fact that certain of them grow in 
moss-like clusters, are common members of 
our marine fauna and yet they are known to but 
very few persons. They are known also as 
Polyzoa from the fact that they are colonial in 
habit. The individuals are minute, rarely as 
large as the head of a pin and usually much 
smaller, yet their power of asexual reproduction 
by budding is so highly developed that they 
often form considerable masses. 
In habit of growth they are extremely varied. 
Perhaps the commonest method is that of en- 
crusting stones, shells, sea-weed, ete., with a 
layer formed of many z00e- 
cia or individual animals. 
They usually remain closely 
attached to each other so as 
to form a continuous crust, 
the walls of which are com- 
monly with 
lime, giving great strength 
and rigidity. Occasionally. 
however, the walls may be 
merely horny or even gela- 
tinous, and in a few 
the walls are covered with 
earthy matter which renders 
them inconspicuous against 
the sea bottom. In the case 
of many of these encrusting 
species one layer may form 
upon the top of another, the 
lower one dying and leaving 
impregnated 
Cases 
SOCIETY 
BULLETIN. 
only its lime skeleton, and 
this process may go on un- 
til a considerable 
formed, consisting of many 
dead layers and a superficial 
living one. Such masses may 
be merely flat layers or they 
may form nodules by com- 
pletely enclosing shells or 
pebbles, .or less commonly, 
they may_rise free from the 
encrusting base in frill-like, 
tree-like or cup-like forms, 
not infrequently of great 
beauty and symmetry. 
In another common meth- 
od of growth the colony is 
erect from the beginning. 
In such species the first in- 
dividual of the colony 
(known as the “‘ancestrula’’) 
attaches itself and the sub- 
developed from it in such a 
as to form a branching, tree-like colony 
often very complex. Usually these forms are 
flexible, either by means of definite joints situ- 
ated at certain intervals (nodes), or else the 
whole colony is uniformly flexible by reason of 
the pliability of the walls of the zooecia or 
their looseness of articulation. 
While all the Bryozoa reproduce asexually by 
budding, they also produce eggs which develop 
into free-swimming ciliated larvae. These are 
so different from the adult individuals that they 
were not at first connected with the Bryozoa, 
but were described separately. The best known 
of these larval forms is the larva of- Membrani- 
mass is 
sequent ones are 
manner 
SMITTIA NITIDA, AN ENCRUSTING SPECIES. 
Natural size. Photo by R. C. Osburn. 
