Travel Reference
In-Depth Information
The mollusks, like the arthropods, are distant from us on the animal evo-
lutionary tree. But there is no doubt about our ultimate kinship with them,
because we share divergent but still detectably similar DNA sequences.
Like the arthropods, the mollusks occupy their own phylum. The family
tree of the mollusks can be followed back through the fossil record for more
than half a billion years, chiefl y because the limestone shells that many of
them construct make excellent fossils.
The name mollusk simply means “soft of body,” a catchall category if ever
there was one. Pioneering Swedish taxonomist Carolus Linnaeus grouped
them into the single phylum Mollusca, recognizing the anatomical similari-
ties among their diversity.
Many mollusks are protected by hard shells, and live most of their lives
in one place. Here at Lembeh, giant Tridacna clams are fi rmly buried in the
mud amid clumps of coral. These clams have shells so large that they have
often been used for baptismal fonts in churches. These huge animals must
fi lter vast amounts of water for food. They get an additional shot of energy
from tiny photosynthetic symbiotic algae that live in their soft mantles and
give them their richly patterned blue, green, or brown colors. When the
clams reproduce they spew forth great fountains of eggs or sperm into the
surrounding water. The resulting larvae are carried away in the (mostly vain)
hope that they will fi nd somewhere to settle and eventually grow up into
new giant clams like their parents.
Tridacna clams stare blurrily at the world through thousands of tiny
window-like eyespots that can perceive only light or dark. Other shelled
mollusks have more elaborate eyes that are highly sensitive to motion. Some
of these eyes are faceted like the eyes of insects. Others are like miniature
versions of the refl ecting telescopes used by astronomers. All of these eyes,
however, only form impressionistic images of the animals' surroundings.
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Other members of this great phylum have abandoned sight but embraced
movement. The shell-less snails called nudibranchs (“naked gills”) are the
dazzling butterfl ies of the sea. They come in a rich variety of colors and pat-
terns. On the seafl oor at Lembeh I encountered an especially gorgeous nudi-
branch, the giant pink-colored
Ceratosoma trilobatum
, as it slid down a clump
