Sponges have the least complex body structure of all multi-celled
creatures. A typical sponge is composed of an outer layer of tissue
and a fibrous inner layer impregnated with numerous glass-like slivers
of silica or calcium carbonate.
The outer surface is riddled with
small openings, joining a complex network of internal canals, through
which water circulates. The inner canals are lined with special
feeding cells, which are equipped with thread-like tails. Vigorous
movements of these tails create a current that moves food-laden
water through the sponge.
A typical sponge pumps water equal to
5 times its own volume every minute. For a football-sized sponge
this translates to several thousand liters each day.
on micro plankton and bacteria. Many sponges live, same as corals,
in symbiosis with algae in their living tissues.
to 70 cm
This species often hosts a variety of other organisms
like crabs, shrimps, worms and fishes.
They use the sponge
to gain access to plankton-rich currents passing above.
Coral reefs are well and truly riddled with worms. Most reef worms
are very inconspicuous. They live in a variety of microhabitats,
particularly the myriad crevices and fissures that are common on
At the first glance FLATWORMS (Polyclads) can be
easily mistaken for nudibranchs. They have a flattened, oval body
and exhibit dazzling color patterns. Their bright colors probably
warn predators that they are toxic or distasteful.
Most common worms
inthe coral reefs around the Similan Islands are SEGMENTED WORMS (Polychaeta). They have a variety
of shapes and life styles. Young worms settle on coral heads and
secrete a tube that kills the underlying polyps. New coral growth
quickly surrounds the tube. Meanwhile the worm occupant secretes
additional tube material to keep pace with the coral. The worm lives
permanently in this tube. Only the brightly colored, feather-like
feeding tentacles protrude from its lair.
RIBBON WORMS (Nemertea)
are also very common on Phuket's reefs. Their bodies are flattened and elongated.
Most species are very small and although many are brightly colored,
they mostly live hidden under rocks or dead corals or in soft bottom
ACORN WORMS (Hemichordata) live on sand or silt bottoms
in U-shaped burrows. Although the animals themselves are not usually
seen by divers, they deposit distinctive coils of sand above the
to 3 cm
Because of its bright colors, this worm is very popular with
divers. Settles in big colonies on hard corals of the species
This species is ultra sensitive to light and pressure
changes. When disturbed they are quickly withdrawn into the