In the first two parts of this series,
I have described difficulties in establishing the identity
of corals, especially to a species level. I have focused on
the Scleractinia, or stony corals, because of all the groups
(and as difficult as they are!), they are the easiest to identify
in most cases. For groups without any real physical material
to examine, identification becomes even more difficult.
In stony corals, I explained, one is faced
with using limited traits to establish a proper identity.
Even if skeletal characters are visible in a living coral
at all, reaching a species identification ranges from relatively
easy for a few, to difficult or impossible for the majority.
Soft corals and gorgonians do have some skeletal elements
to use in identification, but they are not visible or useful
at all in the living coral. Zoanthids and corallimorpharians
have no skeletal elements at all. Thus, in these groups, taxonomy
is based on other characteristics. As with stony corals, identification
may be more precise using molecular techniques. Only a handful
of stony corals have been examined in this manner, and they
are FAR more well-studied, as a group, than any discussed
here. Consequently, the identification of some of these animals,
even if it were possible for the aquarist using various skills
and techniques, is completely negated by the fact that the
actual identification may not be known at all. In the first
part of this article, I described the use of type specimens,
where a specimen in question is compared to a known species
example. For many of the organisms here, no type specimens
exist, and many found in museums or collections are likely
to be incorrectly identified, so that no valid comparisons
are possible at all. To compound the problems in species identification,
even generic or familial level identifications may be extremely
difficult or not properly classified.
The octocorals (soft corals, stoloniferans
and gorgonians) are hard to identify, even to a genus level.
Part of the problem is that there are no visible skeletal
structures in living corals to help aid in the identification
process. Most soft corals contain spicules of calcium carbonate,
called sclerites, within their tissues. The shapes and sizes
of the sclerites are often different in the polyps, the base,
and the interior. They may be loosely present throughout the
tissue (as in members of Xeniidae), tightly packed (as in
some Sinularia spp.) or even fused (as in most gorgonians
axial material). Furthermore, sclerites can be variable. The
color and arrangement of the sclerites must also be considered
for accurate identification. The sclerites and their features
are used in classical taxonomy, and these must be prepared
from living tissue and then examined, usually by scanning
electron microscopy. Even if one were to extract the sclerites
and look at them under a microscope, it is the distinct patterns
of bumps, shapes, and protuberances (tubercles) that must
be considered. Obviously, this is beyond the reach of most
aquarists. Also useful in octocoral taxonomy are chemical
isolates from the secondary metabolites that are produced,
although variability may make these studies somewhat less
accurate. Finally, genetic typing is probably the most accurate
method of identification.
Frederick Bayer (1981) made what I consider
to be the best key to the species of Octocorallia. However,
much of the needed information to key-out species is not available
to aquarists in living corals. I have drawn heavily from this
key in Aquarium Corals (Borneman, 2001), and made use
of visually distinct elements in the identification sections
of the octocoral section. Since this writing, a very important
work has been published entitled Soft Corals and Sea Fans:
A Comprehensive Guide to the Tropical Shallow-water Genera
of the Central-West Pacific, the Indian Ocean and the Red
Sea (Fabricius and Alderslade 2000). In my mind, this
book is a "must have" for anyone interested in the
octocorals from this region. In fact, outside of a few other
limited or less-accurate sources, this may be the only book
of its kind.
The following is a practical method of
establishing the identity of living octocorals:
Identification of soft corals begins with
noting the presence of polyps having eight tentacles that
normally have feathery pinnules along their edges.
|Step 1. Determine the growth form of the octocoral:
|Branched (and branching patterns)
Step 2. Determine if the coral contains
both autozooids and siphonozooids (dimorphic) or if there
are only autozooids present (monomorphic). Autozooids
are the primary feeding polyps and are usually the most visible.
Siphonozooids are usually smaller, appearing as small bumps
without tentacles on the coral surface, and are used mainly
for water flow within the colony.
|Step 3. Note the features of the colony
|Is there a capitulum or polypary (a localized
|Are primary or secondary branches sterile (lacking
|Are sclerites visible through the tissue?
|Are any sclerite arrangements visible (such as
supporting "baskets" around polyps)?
|Does the colony have a rough or smooth feel?
|Is the colony soft or firm?
|Is the colony slippery?
|Does the colony contract or collapse?
|Are the polyp tentacles highly pinnate? Do they
look like feathers or are the pinnules barely visible
on the tentacle?
|Do the polyp tentacles sit atop of stalks (anthosteles)?
The anthostele is the little rod-like element that
the tentacles are perched upon in Sarcophyton and
to a lesser degree in a few other genera.
|Do the polyps have visible, raised, or contrasting
calyces into which they withdraw?
|Do calyces, if present, have a notable shape (rounded,
|What are the locations of the polyps on branchlets
|Do the polyps arise from a mat?
|Is there a significant coenenchyme (matrix in
which the polyps are embedded)?
|Are the colors of the colony indicative of a taxon
(see guidebooks for specifics)?
|Are the polyps a different color from the colony?
|Are there behavioral characteristics:
|Do polyps pulse? Does the colony shed a mucus
tunic? Does the colony contract at night?
|Can the polyps withdraw completely (retractile),
contract (contractile), fold on themselves or are
they completely non-retractile?
|Are there specific branching patterns (single
rods, fingers, nets (fans), anastomosing (interconnected)
branches, branching in a plane, branching in multiple
planes (bushy), lobes, hinges, etc.)?
|If branching, are the branches stiff or flexible?
|Do secondary branches arise directly opposite
each other, in alternating series, as Y-shaped divisions,
|Does the colony drop branchlets?
|Are there stolons (mat-like bases from which the
polyps arise or are embedded) present? Solid layers
|Does the colony have a strong odor out of water?
|How large is the colony?
|Is it zooxanthellate or azooxanthellate?
Step 4. Use the characteristics to assign
a family or genus level designation, if possible, using various
identification guides, such as Fabricius and Alderslade (2001).
Lobophytum sp., note dimorphic polyps:
siphonozooids and autozooids in photo above.
The colony has a short to non-existent stalk, and finger-like
lobed projections. It is quite firm, indicating extensive
Also note gorgonian in background. It is
purple, displays pinnate, planar branching, and the polyps
arise along the edges of the branches (you cannot see this
from the picture, though). It is also zooxanthellate. It is
a Psuedopterogorgia sp.
sp.; note sterile main trunk, primary, and secondary branches.
The colony is quite flaccid, indicating a comparative lack
of sclerite support. The polyps are not retractile, and only
one type are present (monomorphic; autozooids).
Part 3: Zoanthidea
The zoanthids are a horrible lot to classify,
and most current taxonomy is incomplete or inaccurate. Identification
is based on numerous and often variable characteristics. These
may include the tentacle number and arrangement, nematocyst
composition, chemical taxonomy, and other features of the
soft anatomy. The major delineation is whether or not they
are macrocnemic or brachycnemic (i.e. the completion of the
fifth pair of mesenteries). This information is not practically
available in living animals, nor are most of the other required
characteristics. Unfortunately, the classification of most
zoanthids is probably questionable, with very few true species
being accurately characterized and assured (Burnet et al.
1997). Characteristics used to identify zoanthids, including
some characteristics that can be used by aquarists in living
corals, are as follows:
||polyps: colonial or solitary
||polyps: imbedded in coenenchyme or not imbedded
||polyps: connected by stolons or not connected
||polyps: contain sediment inclusions or do
not contain sediment inclusions
||polyps: color may be indicative in some
||zooxanthellate or azooxanthellate
||associations: many zoanthids associate commensally
with other organisms, such as sponges.
Part 4. Corallimorpharia
The last, and perhaps worst, group in which
to try and establish taxonomy are the corallimorpharians,
or mushrooms. Daphne Fautin and some of her associates are
just beginning a long project to identify the phylogeny and
taxonomy of these animals. There are few references on the
taxonomy of corallimorphs, and the best are concerning the
Caribbean species (den Hartog 1980). Earlier descriptions
by Oskar Carlgren, who studied the Pacific animals, are unfortunately
probably not accurate because of inadequate use of defining
characteristics (den Hartog 1980). New molecular probes and
genetic studies have been done for a few species (Chen 1995a,b,c
1996a,b). Like the zoanthids, characteristics used to identify
species are generally unavailable to the aquarist, especially
in living polyps. Corallimorphs do not even have basic delineations
like incomplete mesenteries or incorporation of sediments
with which to separate certain groups. Often, nematocysts
(number and type) and the distribution of surface and marginal
tentacles are used in identification. In terms of physical
characteristics, Aquarium Corals (Borneman 2001) discusses
the features that may be used to distinguish corallimorphs
to a genus level, if in fact the genera names are correctly
assigned at all.
|The visual characteristics potentially used as a guide
||lack or presence of surface tentacles and their
shape (verrucae (short tentacles) papillae (bumps
and warts), etc.)
||lack or presence of bare zones between tentacles
of upper oral surface and margins
||lack or presence of marginal tentacles
||relative stiffness of base
||potentially the ability of animal to trap prey
by infolding, or if a prey capture response is present
||mode of reproduction (laceration, fission, budding,
||color may be somewhat indicative in some cases.
||degree of coloniality - large colonies, small
colonies, isolated individuals.
Fraught with uncertainty, identification
of the groups discussed here is sometimes possible to a family
or genus level. Practically, or even absolutely, unavailable
distinguishing characteristics are a hallmark of many of the
organisms. To compound the frustration lies the fact that
real systematics and proper identification of many of these
groups is in its infancy and remains largely unknown. Perhaps
surprisingly, aquarists may even be more familiar with some
of these groups than those who study them.
In concluding this series on coral identification,
I hope that the articles have proved enlightening and perhaps
even helpful. I am quite sure I have caused some degree of
confusion, frustration, and...just perhaps... interest in
further explorations of identifying the coral animals we keep
in our aquariums.