38
WORLD ATLAS OF CORAL REEFS
Bryozoans
joined with a hinge ligament. Many reef species are found to
burrow into soft substrates, or become incorporated into the
reef matrix as coral or calcareous algae grow around them.
The majority of bivalves are filter feeders. Groups include
oysters, thorny oysters, scallops, mussels and the giant
clams. This latter group (family Tridacnidae) is restricted
to the Indo-Pacific and all species live in a close association
with zooxanthellae. The giant clam Tridacna gigas can
reach over 1.3 meters in length and weigh over 300 kilos.
Cephalopods (Cephalopoda)
These are the most highly modified molluscs in which the
head, and the eyes in particular, are highly developed,
while the foot has been modified into a number of
tentacles or arms. One major group, the Nautiloidea or
nautili, is largely restricted to deep water and not found on
reefs. The other group (Coleoidea) includes the cuttlefish,
squids and octopuses. All are active predators, with horny
"beaks" developed around their mouth and specialized
suction cups on their arms or tentacles for holding prey
and other objects. All have chromatophores in their skin
and are capable of extrernely rapid color changes which
they utilize for camouflage, but also as a form of communication between individuals.
Most cuttlefish maintain a significant calcareous
"shell" which is internalized, while some squid also
contain vestigial traces of a chitinous shell. Both of these
groups are highly active free-swimming predators, but
neither are numerous or diverse in reef environments.
Octopuses are more widespread, although many remain
hidden during the day.
Individual bryozoans are tiny aniinals with a highly
characteristic feeding device known as a lophophore, a
ring of ciliated tentacles to capture and direct food into
a central mouth. Most lay down a horny or calcareous
skeleton, and are capable of withdrawing into this, and
sometimes closing it with a hard operculum. They are
sessile and colonial. Individual "zooids" in a colony may
show particular specializations. Many are encrusting, but
a number of species form erect plate or plant-like
structures and are known as lace corals. Bryozoans,
although inconspicuous, are numerous on all reefs around
the world, and are often among the first organisms to
colonize newly exposed surfaces. They can play an important role in cementing fragments and consolidating the
reef structure.
Echinoderms
The echmoderms are a diverse and highly conspicuous
phylum. They are divided into five groups, which appear
highly differentiated, but have a few traits in common.
Unlike most organisms, which can be divided symmetrically into two halves or are simply radial (corals
and some worm-like groups), the echinoderms exhibit
pcnta-radial symmetry - their bodies radiate into five
symmetrical parts. All echinoderms also lay down a
calcareous skeleton. Extending from their body surface
they have small tube feet which are important in respiration and in most groups also serve a role in locomotion.
Left: A scallop Pedum spondyloideum - this species does not bore into the coral, but the coral has grown up around it.
Right: A cuttlefish Sepia sp. hovers over a solitary mushroom coral Fungia.
WORLD ATLAS OF CORAL REEFS
Bryozoans
joined with a hinge ligament. Many reef species are found to
burrow into soft substrates, or become incorporated into the
reef matrix as coral or calcareous algae grow around them.
The majority of bivalves are filter feeders. Groups include
oysters, thorny oysters, scallops, mussels and the giant
clams. This latter group (family Tridacnidae) is restricted
to the Indo-Pacific and all species live in a close association
with zooxanthellae. The giant clam Tridacna gigas can
reach over 1.3 meters in length and weigh over 300 kilos.
Cephalopods (Cephalopoda)
These are the most highly modified molluscs in which the
head, and the eyes in particular, are highly developed,
while the foot has been modified into a number of
tentacles or arms. One major group, the Nautiloidea or
nautili, is largely restricted to deep water and not found on
reefs. The other group (Coleoidea) includes the cuttlefish,
squids and octopuses. All are active predators, with horny
"beaks" developed around their mouth and specialized
suction cups on their arms or tentacles for holding prey
and other objects. All have chromatophores in their skin
and are capable of extrernely rapid color changes which
they utilize for camouflage, but also as a form of communication between individuals.
Most cuttlefish maintain a significant calcareous
"shell" which is internalized, while some squid also
contain vestigial traces of a chitinous shell. Both of these
groups are highly active free-swimming predators, but
neither are numerous or diverse in reef environments.
Octopuses are more widespread, although many remain
hidden during the day.
Individual bryozoans are tiny aniinals with a highly
characteristic feeding device known as a lophophore, a
ring of ciliated tentacles to capture and direct food into
a central mouth. Most lay down a horny or calcareous
skeleton, and are capable of withdrawing into this, and
sometimes closing it with a hard operculum. They are
sessile and colonial. Individual "zooids" in a colony may
show particular specializations. Many are encrusting, but
a number of species form erect plate or plant-like
structures and are known as lace corals. Bryozoans,
although inconspicuous, are numerous on all reefs around
the world, and are often among the first organisms to
colonize newly exposed surfaces. They can play an important role in cementing fragments and consolidating the
reef structure.
Echinoderms
The echmoderms are a diverse and highly conspicuous
phylum. They are divided into five groups, which appear
highly differentiated, but have a few traits in common.
Unlike most organisms, which can be divided symmetrically into two halves or are simply radial (corals
and some worm-like groups), the echinoderms exhibit
pcnta-radial symmetry - their bodies radiate into five
symmetrical parts. All echinoderms also lay down a
calcareous skeleton. Extending from their body surface
they have small tube feet which are important in respiration and in most groups also serve a role in locomotion.
Left: A scallop Pedum spondyloideum - this species does not bore into the coral, but the coral has grown up around it.
Right: A cuttlefish Sepia sp. hovers over a solitary mushroom coral Fungia.