Bivalve mollusks are amazingly diverse
in form. and their beauty strikingly perfect. Necklaces and amulets
made of bivalve shells can adorn the human body and household interiors,
vases incrusted with their pearly fragments promote good mood and lofty
inspiration, and the poetic depiction of Venus by a famous artist
from Florence also associate her birth with mollusk shells, the bivalves,
as you have already probably guessed.
Bivalve mollusks are widespread in
all seas of the World Ocean. However, the number of their species may vary
depending on the geographic latitude and hydrographic
specifics. For instance, whereas there are about seventy
bivalve species in the Arctic, their number in the coastal seas of Siberia
normally does not exceed 30-35 species. In the Chukchi Sea, the number
of bivalve species increases to 40-50, and in the Bering Sea to 60-65.
The specific diversity of bivalves increases even more to the south. In
the Sea of Okhotsk, they number from 80 to 90; in the northern part of
the Sea of Japan, from 120 to 130; and in its southern part, to about 200
species. From 200 to 240 species inhabit the Yellow and East China Seas.
In the South China Sea, including the Pacific coast of the Philippines,
there are more than 300 different bivalve mollusk species.
With regard to diversity of bivalve
species, the coast of Primorye is subdivided into two areas, the northern
and southern; the boundary between them may be drawn at Cape Povorotnyi.
In the northern area washed by the cold Primorye current, the bivalve specific
diversity on the average normally does not top the 70-75 mark to increase
in bays and decrease in open coastal sites. In the southern area, the number
of species compared with that inhabiting the northern area abruptly rises
to 110-120. Among other things, this is caused by the highly uneven shore
line. Shallow inlets and deeply indented bays allow species of different
geographic origin to exist here, including local or low-boreal species
inhabiting both open shelf areas; those from cold water or high-boreal
and arctic areas, inhabiting chiefly open shelf sites; and warm-water or
subtropical species occurring in the most heated sections of bays and for
whom Peter the Great Bay is essentially a refugium.
The body of a bivalve mollusk is enclosed
in a calcareous shell consisting of two valves. The sizes of adult specimen
shells of Primorye species vary from 2-3 to 200 mm. The thickness, form,
sculptural decorations, projections (teeth) inside, the color outside and
inside the shell and other morphological properties also vary widely, and
in conjunction with the anatomy of the soft mollusk body is
essentially an object of taxonomy, the science of classification of living
The soft body consists of a mantle
or fold lining the shell from inside, gills, oral blades Ц lamellate outgrowths
that sort food particles; arms that help the shells to dig in, move and
fasten to rocks by means of special byssus threads; and a visceral mass
containing a digestive gland (liver analog), a stomach, an intestine, a
pericardial bursa (heart), kidneys and reproduction organs.
Most species reproduce by external fertilization, when male and female
gametes are simultaneously spawned to meet outside the organism. Fertilization
results in a larva which lives deep in the water to grow from 120-150 to
300-400 microns. After a while, lasting from one week to one month and
over, the larva settles on the sea floor to lead a lifestyle largely similar
to that of adult specimens.
Despite the fact that Primorye has
long been an object of research, the biology of many of its
bivalve mollusk species still remains insufficiently studied for a variety
of reasons. Some species occur rarely in general, not only in Primorye,
while others do not form regular populations and we are aware of their
presence only on seeing empty shells. Again, basing on their distribution,
we believe that some of their biological properties have been relatively
well studied on populations from other areas. Yet, quite often it happens
that we are speaking of morphologically similar, albeit different
species that vary in additional properties studied neither in Primorye,
After the mollusks die, the shells
of species inhabiting small depths (of up to 20 m) normally surface to
the sea floor. When the weather is windy or stormy, they are ejected onto
gently sloping sand beaches to not infrequently form large accumulations
that turn an empty coast into a motley carpet of colors. At the same
time, the life of empty shells on beaches is ephemeral. Under the impact
of waves, high tides, gales and precipitation, some of them sink again
to hardly accessible depths, while others (the most fine and brittle ones)
are destroyed. However, after a while, a new storm
bring new shells.
So, when you bake in the sun on the
yellow sand of a Primorye beach, noting all the variety of life, please
take note of the shells lying around. Their appearance can help you distinguish
bivalve mollusk species, the first essential step in learning the life
of sea creatures. Having learned to determine the species, you could bring
order to your initially modest shell collection (to possibly promote your
future career!). Finally, a shell collection may help you make various
articles and ornaments to harmonize your surroundings.
The following descriptions of Primorye
bivalve species are almost similar to the wording and style of scientific
descriptions found in special taxonomic literature. Taxonomy is the
most ancient of sciences, and its terminology is simple and readily understandable.
Once you learn it, it can, among other things, be your first bridge to
the fascinating mysteries of bivalve mollusk life.
Significantly, most species have neither
Russian, nor local indigenous names. So shell lovers make good use of Latin
names given by biologists to each respective species.