Generally,
the early cycles extend inward farthest and the last cycles the
least. An axial structure called the columella may be present
in some corallites. When a columellar structure is present
it may consist of a solid rod, a mass of vertically twisted threads
and ribbons, or it may be formed of the enmeshed and twisted marginal
teeth of septa which reach the 'central part of the corallite.
So far
solitary corallites or groups of corallites in a colony that were
either fused together or separated by a zone of coenosteum have
been discussed. New corallites within a colony basically
arise by two common modes of asexual reproduction, which to a
large part determines the form and shape of both the corallites
and the corallum. The first of these modes is by intratentacular
budding whereby two, three, or more mouths develop within the
circle of tentacles at the oral end of the polyp. These
new mouths may subsequently separate and each develop their own
circle of tentacles (especially in the case where only two or
three mouths develop), or they may remain within the original
tentacular ring. In the latter case, the tentacular ring
may enclose two mouths and form an oval-shaped polyp, three mouths
and form a triangular or somewhat elongate polyp, or four or more
mouths and form a very elongate polyp that can undergo complex
modification by branching or forking or become long and sinuous.
As you can see from the illustrated examples in Text
Figure A, the polyps and subsequent corallites can be quite
variable in shape and form, even within the same corallum. The
second less complex mode of asexual reproduction is by extratentacular
budding whereby new polyps arise outside the tentacular ring of
existing polyps. In this mode the new polyp mouth may develop
in close association with an existing polyp, such as in the costal
region, or more distant from it in the intervening zone of coenosarc.
In either case the new polyp eventually looks much the same
as others within the colony. A third less common mode of asexual
reproduction occurs in the Family Fungiidae, whereby a cylindrical,
attached corallite develops a flaring table-top shaped calice
at its upper end as in Fig. 344.
Transverse fission then splits the flattened upper portion
off and produces a new unattached individual. The still
attached individual may repeat the process an produce a number
of such free-living offspring. In addition to being able
to recognize the various kinds of polyps and their associated
skeletal parts to use the annotated key in this handbook it will
also be very useful to recognize the shape or form of the corallum
that ultimately develops as a result of growth and asexual reproduction.
Even in similar-looking, closely related species there is
nearly always some distinctive feature in either the corallite
or corallum form, or in both, that sets them apart from each other.
Colony Form in Solitary
Coralla
The solitary
coralla encountered in Guam's shallow-water coral communities
include the attached and unattached forms illustrated in Text
Figure A. Attached forms are generally small but in
some restricted habitats they may be quite abundant. Conical-shaped
coralla are called ceratoid if the basal angle is low (20) , trochoid
if medium (40) , and turbinate if high (70). If the corallum
is relatively long (ht. > dia.) and the diameter is about the
same throughout its length, it is called cylindrical, and if relatively
short and squat (ht. < dia.), it is tympanoid. The most
conspicuous and largest of the solitary corals are the unattached
discoid coralla in the family Fungiidae. In these coralla
the oral surface may be flat, slightly concave, or convex with
an aboral surface that is either flat or concave. The peripheral
outline of the coralla may be circular, oval, or elongate. Many
of the colonial unattached fungiids are of similar form but have
more than one calice on the oral surface.
Colony Form in Colonial
Coralla
Form in
colonial coralla is expressed in a wide variety of shapes that
depend to a large extent upon the mode or manner in which new
corallites are added to the colony.
