Page 4 - Lecturer_1

Physiological Processes

Molting and Growth

Since the shell of the lobster is hard and inelastic, it must be shed
periodically in order for the animal to grow. The act of escaping from

the old shell is known as ecdysis (from the Greek, ekdysis, meaning
"getting out") or, more commonly, as shedding. The term molting is used
to refer to the entire cyclical process of preparing for, undergoing, and
recovering from ecdysis. For lobsters, molting is a continual process
because lobsters show indeterminate growth; that is, they grow
throughout their lives and therefore spend much of their time either
preparing for or recovering from ecdysis. (Females take a break from the
molting process when they are carrying eggs or when they are preparing
to extrude another set of eggs.)

To prepare for ecdysis, the lobster lays down a new exoskeleton
underneath its old one. This new exoskeleton is complete in every detail,
with every spine, bump, hair, and pigment present. If any limbs have
been lost, they begin to regenerate. Minerals are removed from the old
exoskeleton and stored in large gastroliths on either side of the cardiac
stomach wall. Blood is removed from the claws and other limbs which
causes them to shrivel and the lime in the joints of these appendages
dissolves. By the time the lobster is several days away from shedding,
certain areas of the exoskeleton, where reabsorption of minerals has
occurred, are very soft and appear bluish in color. Just prior to molting,

the lobster drinks in water and absorbs it through its now very
permeable gut. This water intake causes the new exoskeleton to swell,
pushing apart the old carapace.

During the molting process, the lobster lies on its side and its shell
opens along the cephalothorax/abdomen interface. Softened joints
allow the lobster to withdraw its shriveled limbs from the old skeleton -
- all appendages, including the legs, gills, mouthparts, antennae,
antennules, eyestalks, and pleopods are withdrawn. In addition, the

digestive system is shed and the ossicles holding the gastroliths in place
are lost, resulting in the gastroliths falling into the cardiac sac and being
dissolved by the digestive juices. The freed minerals then pass back into
the hemolymph (the lobster's combined blood and lymphatic fluid) and
are redeposited in the new soft shell