The scallop is a mollusc, a member of the very
large group of animals which include the oyster and the whelk. The
scallop belongs to the bivalves, a sub-group which is distinguished
by having a pair of shells.
Scallops have a single, large abductor muscle for closing the valves
(Outer Shells). At the edge of the mantle (the soft tissue in contact
with most of the valve surface) are short tentacles that hang like
a curtain between the valves when they are open. The tentacles detect
changes in the composition of the watery medium. Also at the edge
of the mantle are eyes. About fifty of these, green ringed with blue
are set in the frill, not to show where they are going, since they
are always going in the other direction, but to warn them of danger
approaching.
Scallops are hermaphrodites with each roe containing the male (whitish
testis) and female (orange ovary) sex organs.
The shells are marked with concentric annual rings denoting the age
of the scallop - one ring per year.
The king scallop is caught when 10-15cm in diameter, 6-7 years growth
- it has a flat upper shell and a convex lower shell.
The queen scallop seldom exceeds 9cm when caught, 2-3 years growth
- both of its shells are rounded.
Scallops are most commonly found
in a fine sand or shingle sea bed in relatively clear water. They feed on microscopic
plants and animals. Cilia (tiny hairlike structures) and mucus aid
in the collection and movement of food particles towards the mouth.
Scallops are unusual as bivalves in their ability to swim, which they
do by spasmodic clapping movements of the valves; water ejected in
jetlike spurts, propels the animals forward.
During reproduction eggs and sperm are shed into the water, where
fertilization occurs. The eggs develop into free-swimming larvae.
In the next developmental stage they settle onto the bottom; some
have the ability to crawl. A byssal gland develops and is used to
attach the animal firmly to the bottom or to some other solid surface.
Some scallops remain attached throughout life; others break free and
become spasmodic swimmers.
Scallops are gregarious creatures, they sometimes congregate in thousands
of favoured beds of clear, fine sand, and they occur in small numbers
anywhere that the bottom is suitable between depths of 60 and 500
feet.
The most important predator of scallops is the starfish, which attacks
by wrapping its arms about the valves and, by the sucking action of
its tube feet, pulls the valves apart; it then inserts its stomach
between the valves of the scallop and digests the soft part.
King
ScallopPectenmaximus
English
King Scallop
French
Coquille Saint-Jacques
Spanish
Vieira
Remarks
Maximum diameter about 15cm. The shell is usually whitish, brown or
pinkish.
Queen
ScallopChlamysopercularis
English
Queen Scallop
French
Noix de Petoncle, Noix de St Jacques
Spanish
Zamburina
Remarks
Maximum diameter about 9cm, average size 6cm. The shell is almost
circular and has about twenty ribs. Its colour may be yellow, orange,
pink, red. The queen usually inhabits deeper waters than the king.
