Mushrooms, Elephants Ears, and False Corals:A review of the Corallimorpharia
The
order corallimorpharia, in the phylum Cnidaria, class Anthozoa, includes
anemone-like and coral-like creatures that are very popular in the
aquarium hobby due to their hardiness and fantastic range of color and
form. Corallimorphs are, as their name implies, very coral-like, but
they do not secrete a skeleton. They have radially arranged tentacles or
pseudo tentacles, if present. The most popular varieties contain
symbiotic zooxanthellae, so their maintenance involves providing
sufficient light for photosynthesis by the zooxanthellae. This is not
too difficult to achieve for most species, as many of them seem to
prefer low light levels or indirect light. Standard fluorescent lights
are fine for many, but not all varieties.
Even
the symbiotic species feed on a variety of external food sources. All
feed on dissolved and particulate matter, some feed on zooplankton, and
some even trap and eat fishes! Tiny cilia on the surface of the oral
disc help transport trapped dissolved and particulate material to the
mouth. Larger prey are trapped by the formation of a sac when the edges
of the oral disc fold upwards and meet at a central point. The genera
that lack symbiotic zooxanthellae feed actively on large and small prey,
mostly zooplankton, using potent nematocysts located on numerous long
tentacles.
Reproduction
in Corallimorphs is achieved mainly vegetatively (budding,
fission, pedal laceration), and the formation of colonies of
clones is common for most species. Though it certainly occurs in
nature, sexual reproduction involving the release of eggs and
sperm by polyps of separate sexes is not well documented. Aquarium
observations have so far been of egg release only, and there have
not been any reports of new recruits of sexually produced
offspring.
Only
a few specialists have attempted to classify the corallimorpharia,
and the systematics for them is presently incomplete. For example,
there is not a clear dividing line between some forms classified
as Discosoma and some forms classified as Rhodactis. The two genera seem to merge, and the taxonomist J.C. DEN
Hartog tended to group them together as Discosoma,
though he still recognized Rhodactis
as valid for at least some species.
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Discosoma
The
common "mushroom anemones" or "Elephant ear
mushrooms" or "Disc Anemones" belong to the genus Discosoma. Generally they are disc shaped with a conical mouth, and
the oral disc may be smooth, ribbed, with small or large pseudo
tentacles or none at all. The edge of the oral disc may form
pointed lappets or it may be uniformly circular as if cut by a
cookie cutter. The consistency of the tissues is thick and, due to
copious mucus production, they are slippery to the touch. They are
the hardiest genus for aquarists, and most species thrive even
under low light intensities. However, the metallic blue varieties
keep their color best under strong illumination. Fluorescent
orange and green varieties are spectacular to observe under blue
light. Discosoma spp.
tolerate strong water flow, but open largest under low velocity
water currents. Strong lighting may cause them to curl the oral
disc, and even bleach (lose pigment and zooxanthellae). I have
been able to reverse this bleaching with the addition of a trace
element supplement containing iron and manganese that I found
promotes the health of zooxanthellae. My observations in this
regard are anecdotal.
The
common red, blue, green, brown, spotted, or pinwheel striped Discosoma
sp. from Indonesia is a highly variable single species. Some authors
have suggested that the different forms are distinct species, but this
does not appear to be the case. Single polyps with a combination of
features (for example, pinwheel and solid color) occasionally occur, and
the range of patterns and colors merge. The presence or absence of
vesicles on the oral disc is also highly variable. The identity of this
variable species is not known, since its many forms have received
different names. The most likely name is Actinodiscus nummiformis, originally described as Discosoma
nummiforme in 1828. Discosoma
fowleri, described in 1888 may be the same species. A second species
from Indonesia has more distinctly defined lappets at the perimeter of
the oral disc and is slightly smaller in maximum size, see photos. Both
species live principally on the photosynthetic products of their
symbiotic zooxanthellae, and they supplement this with dissolved organic
food absorbed from the water, and particulate matter trapped in mucus
and carried by cilia to the mouth. I have seen some specimens envelop
and eat flake food or blackworms, but only in situations where they
occur in very low water velocity. They close up very slowly and water
currents tend to blow food out of their "grasp." The
Indo-Pacific Discosoma spp. rapidly reproduce by pedal laceration, budding, and
transverse fission.
The
two Discosoma spp. from the
Caribbean have been collected and imported recently from Haiti in
sufficient numbers that they have now become readily available to
hobbyists. Discosoma neglecta, the umbrella corallimorph, is a spectacular
polyp with pronounced tongue-like lappets. It achieves a maximum
diameter of about 15 cm and is typically bright fluorescent green,
brown, or a combination of the two. Rare specimens are orange or
turquoise. Discosoma neglecta feeds readily on chunks of shrimp or fish, and
also takes pellet food or flake food. Discosoma
carlgreni is closely related, and the two may sometimes hybridize,
confusing the distinction between them. Discosoma
carlgreni has more numerous and smaller lappets at the margin of the
disc, and it has more numerous pseudotentacles. These pseudotentacles
are also branched in large specimens, whereas in Discosoma
neglecta the pseudotentacles are more lobe-like. Both Caribbean
species of Discosoma reproduce in aquaria by budding and pedal
laceration, but in my experience colonies grow much more slowly than
Indo-Pacific Discosoma, even
when they are fed regularly.
Discosoma
(=Actinodiscus) nummiformis blue form from
Indonesia. To keep this bright blue color they require strong
illumination.
Discosoma
(=Actinodiscus) nummiformis blue pinstripe form
from Indonesia. These don't require as much light as the solid
blue form.
Discosoma
(=Actinodiscus) nummiformis green pinstripe form
from Indonesia. These fluoresce brilliantly under blue light.
Discosoma
(=Actinodiscus) nummiformis Red form from
Indonesia. These fluoresce brilliantly under blue or green
light.
Discosoma
sp. from Indonesia. The vesicles on the oral discs of this
colony are reminiscent of the tentacles of Ricordea spp.
Discosoma
carlgreni
from Florida and the Caribbean. Note branched Pseudotentacles on
the oral disc and the numerous small lappets at the disc margin.
D. carlgreni are usually turquoise, but occasionally are
orange.
Discosoma
neglecta
photographed at Riverbanks Zoo and Aquarium. This six inch
diameter specimen shows the typical elongated lappets on the
disc margin.
A
colony of Rhodactis sp. in the Solomon Islands. Such
densely packed colonies are produced by pedal laceration and
fission.
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Rhodactis
Rhodactis
spp. have an oral disc covered with pseudotentacles that are
usually branched. The edge of the oral disc in most species has
toe-like tentacles, and there is often a naked tentacle-free
margin separating the central oral disc from the edge of the disc.
Some species have thick tissues, but many have rather thin
tissues, much thinner than in typical Discosoma.
Most are also slippery to the touch. Rhodactis
spp., except R. cf.
mussoides actively feed on fleshy food when it is offered,
folding up the disc margins to envelop the food. The tentacled
varieties of Rhodactis spp. tolerate and prefer much stronger light and water
motion than most Discosoma
spp. Large species of Rhodactis
can trap fishes, in the same manner as the related genus Amplexidiscus.
Rhodactis spp. reproduce
by fission, pedal laceration, and a type of budding that involves
the formation of gemmules both internally and on the surface of
the oral disc (Sprung and Delbeek, 1997).
From
Indonesia there are many varieties of Rhodactis,
whereas the Caribbean has just one species, R.
sanctithomae, also known as Discosoma
sanctithomae. It has branched pseudotentacles and a naked
region next to the disc margin. Occasionally the pseudotentacles
are not branched, being grape-like vesicles instead. This form
once was given a different name, Orinia
torpida. Rhodactis sanctithomae feeds on zooplankton and takes all kinds of
protein rich foods offered. It prefers strong illumination, but
should be oriented vertically on rocks or walls, not facing the
light directly.
Rhodactis inchoata from the Indo-Pacific has thicker tissues than
many other Rhodactis
spp.,
and it is often very colorful. The disc margin has toe-like
tentacles. The purple Tonga mushroom is R.
inchoata, and there are distinctive multicolored green, blue,
and red specimens imported from Indonesia. It does not require
supplemental feeding and does not feed as readily as other species
in the genus.
Two
other forms of Rhodactis
imported from Indonesia include the "Giant Green Metallic
Mushroom," which is an undescribed species, and another
undescribed species that has pseudopolyps that mimic the polyps of
the coral Goniopora. The
former species grows to over 30cm in diameter, while the latter
grows to about 20 cm. The former readily feeds on chopped shrimp
or pellet foods, and grows to enormous size under fluorescent
lighting. An additional species, tentatively identified as Rhodactis
mussoides, has very thick tissues like the mussid stony coral Lobophyllia. It is rather like a Discosoma,
lacking tentacles at the disc margin, but it can have multiple
mouths like a mussid coral and like Ricordea
florida. It prefers indirect light. Blue actinic bulbs promote
the development of green fluorescent protein in this species, and
specimens maintained under blue light become intensely green.
This
Rhodactis sp. has pseudotentacles that perfectly
mimic the polyps of Goniopora spp.
Rodactis
sanctithomae
from Florida and the Caribbean is a delicate species, with
thin tissues that are easily torn. It should be fed
frequently to encourage it to grow and divide, and it
prefers strong indirect light.
Rhodactis
sanctithomae
sometimes forms rounded vesicles on the oral disc. This
form was once described as a distinct species.
The
purple Tonga mushroom, Rhodactis inchoata, comes in
numerous color combinations that sometimes blend
surprisingly well with live rock.
The
giant green metallic mushroom from Indonesia is an
undescribed Rhodactis sp.
This
exceptionally large colony of Amplexidiscus fenestrafer
was photographed on a reef slope in the Solomon Islands.
Normally this corallimorph occurs in groups of four or
five polyps. For size reference, each large polyp is
approximately 10 inches in diameter.
Amplexidiscus
Amplexidiscus
appears like an extremely large Rhodactis,
but it is distinguished by some features of its nematocysts. It also
grows slightly larger than most Rhodacits
spp., with a maximum diameter of approximately 20 inches (50 cm). Amplexidiscus
fenestrafer is the only species recognized in the genus, though
there may be a second species according to a researcher named Chen
(Charles Delbeek, pers. comm.). Amplexidiscus fenestrafer is a piscivore, and it apparently uses an
attracting and intoxicating scent to lure fishes into the folds of its
oral disc. It slowly closes around the fish until it has trapped it
within the sac formed, and then it digests the fish with mesenterial
filaments. In the aquarium Amplexidiscus
fenestrafer can trap fishes, but it can also be maintained and fed
dead fish. Most fish learn to avoid it, but there is always a risk
that Amplexidiscus fenestrafer will trap and eat your favorite fish.
Reproduction in A. fenestrafer
is typically by pedal laceration or budding, but fission is
occasional.
Ricordea
Ricordea
spp. have vesicle-like tentacles on the oral disc. While some species
of Discosoma and Rhodactis may develop vesicles on the oral disc, there is no
mistaking them with the pronounced tentacles of Ricordea. One look-alike that can be confused with Ricordea
is Stichodactyla tapetum (Sprung, 2001). The latter has sticky
tentacles while the former does not. Both can form colonies of
numerous individual polyps approximately 5 cm in diameter. Both
reproduce by fission. Stichodactlya
tapetum also has a form that may grow to 30 cm in diameter. The
maximum size for Ricordea is about 15 cm in diameter. There are two
widely recognized species of Ricordea, R. florida from
the Atlantic and Caribbean, and R.
yuma from the Indo-Pacific region. Both are very popular in the
aquarium trade. Ricordea yuma
is readily distinguished from R.
florida by the fact that the former has pseudotentacles on the
oral cone, while the latter does not. Also, R.
florida often has numerous mouths and elongated irregular polyps,
while R. yuma is usually
circular, with one mouth. All are spectacular due to the grape-like
tentacles on their oral disc, but some especially prized specimens
have brilliant fluorescent proteins in shades of orange, red, pink,
blue, and green.
Pat
Gibbs and his students at the University of Miami have been able to
isolate the genetic material that produces these colors in Ricordea,
and put it into the freshwater zebrafish, Danio rerio. Under blue light they fluoresce brilliant green,
orange, or blue, like the Ricordea
polyps from which the pigments were derived.
Ricordea
spp. prefer moderate currents and moderate to strong illumination.
They may reject some foods offered, but they will take live blackworms.
Some specimens reproduce slowly, while others do so more quickly,
given the same conditions. The rate of reproduction is thus apparently
genetically determined (Pat Gibbs, pers. comm.).
Closeup
of a polyp of Ricordea florida.
A
stunningly fluorescent orange Ricordea yuma. Such
polyps are rare and command a high price.
Colorful
varieties of Ricordea yuma from Indonesia
Even
plainly colored specimens of Ricordea yuma are
beautiful. This solitary specimen was photographed in deep
water in the Solomon Islands, along with a commensal
Periclimenes shrimp.
Pseudocorynactis
caribbaeorum
reproduces by fission. Here a single polyp has divided into
four.
This
Pseudocorynactis from Fiji is beautiful but not safe
with fishes and adjacent invertebrates. It is a voracious
eater that has powerful nematocysts in the ball-like tentacle
tips.
Corynactis
Corynactis
spp. are mainly temperate species, known as Strawberry anemones. They
are small, not usually larger than one inch (2.5 cm) in diameter, and
colonial, reproducing by fission and pedal laceration to cover large
areas of rocks. Tropical species may occasionally be introduced to
aquariums with live rock. The tropical species are less colorful, tend
to be cryptic, and form much less densely packed colonies. All Corynactis
spp. feed on zooplankton and particulate organic matter. To keep them
healthy and encourage division, they need to be fed at least several
times per week. A "milkshake" of chopped seafood can be
used, but they will also take flake or pelletized foods, and frozen
shrimp or worms.
The
expanded polyp of Pseudocorynactis caribbeorum.
Note the orange ball-like tentacle tips for which the
Orange Ball Anemone is named.
Pseudocorynactis
Pseudocorynactis
spp. are like Corynactis
but are much larger (to about six inches (15 cm) diameter, and
usually not colonial. They also reproduce by fission, but it is
unusual to find more than about six clones together as a group.
The so-called orange ball anemones that can be observed on coral
reefs at night are Pseudocorynactis
spp. The column varies in color from cryptic shades of brown to
orange, red and magenta. The tips of the tentacles are commonly
bright orange, but they can also be white. These tentacle tips
are extremely sticky, like flypaper, due to the presence of
powerful nematocysts. This fact makes the larger species from
the Indo Pacific region unsuitable for aquariums housing fishes,
which they readily capture. They also can catch mobile
invertebrates such as shrimps and snails, and sometimes
"attack" sessile invertebrates growing on adjacent
rocks, enveloping them in the gastric cavity through a widely
opened mouth. Pseudocorynactis
spp. can be fed daily, but only require twice weekly feeding to
keep them healthy. If they are not fed frequently enough, they
shrink. There is a marked behavioral difference between the
common Caribbean and Indo-Pacific species.
The
Caribbean species, Pseudocorynactis
caribbaeorum mainly opens its tentacles at night, and closes
rapidly when it senses light. The Indo-Pacific species remains
open both day and night, and is not sensitive to light. The
presence of food smells (dissolved amino acids) in the water
stimulates either species to open up and extend the tentacles,
and the caribbean species can be trained to open in the light by
feeding it during daylight hours. The mechanism for its apparent
memory is not known.
Whether
you have a large reef aquarium or a simple small aquarium, any
of the corallimorphs can be easily maintained and enjoyed for
decades.
Suggested
Reading
Carlgren,
O. 1949. A Survey of the Ptychodactaria, Corallimorpharia and
Actiniaria. Kungl. Sven.
Vetenskapsakad. Handlingar, Ferde Ser., 1, 1-121 + 4 plates.
Dunn,
D.F. and Hamner, W. M. 1980. Amplexidiscus fenestrafer n. gen., n. sp. (Coelenterata, Anthozoa),
a tropical Indo-Pacific corallimorpharian. Micronesica,
16, 29-36.
Hartog,
J.C. DEN 1980. Caribbean Shallow Water Corallimorpharia. Zoologische
Verhandelingen. 176:1-83.
Schlichter,
D., Bajorat, K.H., Buck, M., Eckes, P., Gutknecht, D., Kraus,
P., Krisch, H., and Schmitz, B. 1987. Epidermal nutrition of sea
anemones by absorption of organic compounds dissolved in the
oceans. Zool. Beitr. N.F.,
30, 29-47.
Sprung,
J and J.C. Delbeek 1997 The Reef Aquarium Volume Two Ricordea Publishing
Sprung
J. 2001. Invertebrates: A
Quick Reference Guide. Ricordea Publishing
