Page 282 - (DK) Ocean - The Definitive Visual Guide

280 ANIMAL LIFE

CLASS BIVALVIA
Common Mussel

Mytilus edulis
LENGTH
10–15cm (4–6in)
HABITAT
Intertidal zones,
coasts, estuaries
DISTRIBUTION North and southeastern Atlantic,
northeastern and southwestern Pacific

Also called the Blue Mussel, this edible,
black-shelled bivalve attaches itself in
large numbers to various substrates
using tough fibres called byssus threads.
These fibres are extremely strong and
prevent the mussels from being washed
away. The fibres increase in strength
in autumn perhaps to cope with
storms. When the mussel opens its
shell, water is drawn in over the gills,
or ctenidia, which absorb oxygen into
the tissues and also filter food particles
out of the water.
Common Mussels are very efficient
filter feeders – they process about
45–70 litres (10–15 gallons) of water
per day and consume almost everything
they trap. The sexes are separate and so
grouping together in “beds” helps to
ensure that their eggs are fertilized.
After hatching, the planktonic larvae are
dispersed by the ocean currents. After
some months the larvae settle, attach,
and metamorphose, but can resorb their
byssus and move to a better spot.

Black-lip Pearl Oysters begin life as
CLASS BIVALVIA CLASS BIVALVIA
a male before changing into a female
Black-lip Pearl two or three years later. Females Shipworm
Oyster produce millions of eggs, which are Teredo navalis
fertilized randomly and externally by
the males’ sperm, before hatching into LENGTH
Pinctada margaritifera
free-swimming larvae. The mobile 60cm (24in)
LENGTH larvae pass through various larval HABITAT
Up to 30cm (12in) Wood burrows in
diameter stages for about a month before high-salinity seas and
eventually settling on the sea floor,
HABITAT estuaries
Hard substrata of inter- after metamorphosing into the sessile
and subtidal zones; reefs (immobile) adult form. This species is DISTRIBUTION Coastal waters off North, Central, and
famous and much sought-after South America, and Europe
CLASS BIVALVIA
DISTRIBUTION Gulf of Mexico, western and eastern because it occasionally produces
Great Scallop Indian Ocean, western Pacific prized black pearls. Despite its worm-like appearance, the
shipworm is a type of clam that has
become elongated as an adaptation to
Pecten maximus
WIDTH CLASS BIVALVIA its burrowing lifestyle. Its bivalve shell,
Up to 17cm (7 1 / 2 in) situated at the anterior end, is very
HABITAT Atlantic Thorny small and ridged. The Shipworm uses
Sandy sea beds, at it with a rocking motion to bore into
5–150m (16–500ft), Oyster
commonly 10m (33ft) wooden objects. Outside the shell its
body is unprotected, except for a
Spondylus americanus
DISTRIBUTION Northeastern Atlantic calcareous tube it secretes to line the
LENGTH burrow. These worms damage wooden
1
Up to 11cm (4 / 2 in)
Also known as the King Scallop, the structures, such as piers, irreparably
Great Scallop is usually found partly HABITAT and in the past caused many ships to
Rocks to a depth
buried in sand. It is one of the few of 140m (460ft) sink. The burrow entrance is only about
bivalves capable of rapid movement the size of a pinhead, but the burrow
1
through water, which it achieves using itself may be over 1cm (/2 in) wide, so
a form of jet propulsion. It claps the DISTRIBUTION Southeast coast of USA, Bahamas, the extent of an infestation is often
OCEAN LIFE close to the hinge. It moves forwards The Atlantic Thorny Oyster’s spiny toothed hinge seen in many other female during their lifetime, and the
Gulf of Mexico, Caribbean
two halves of its shell together, which
underestimated until it is too late.
Shipworms change from male to
pushes water out of the mantle cavity
shell protects it from predators.The
female form produces many eggs,
with its shell gape first, producing j
from which free-swimming larvae
oyster pictured here is covered with an rather than the more common
erky movements as it takes successive
hatch. When they mature and settle
encrusting red sponge, which provides
“claps” of water. These movements
camouflage. This species is unusual in
bivalves. The Atlantic Thorny Oyster
are a useful strategy to escape from
on a suitable piece of wood, the larvae
quickly metamorphose into the adult
cements itself directly to rocks rather
predators. These edible bivalves are
having a ball-and-socket type hinge
now farmed to meet growing demand. joining the two halves of its shell,
than using byssal threads.
form and start burrowing.