Tag Archives: Molt

Happy Halloween with Exoskeletons

Happy Halloween! CIMI staff love to wear costumes, but not just on Halloween! We wear them every time we teach squid dissection. You can often see us dressing up like fairies, senior citizens, mad scientists, pirates, and even ghostly skeletons, which brings me to my next point. Did you know crustaceans, like crabs and lobsters, participate in Halloween every day? They wear skeletons on their outsides all the time! Unlike a costume or an internal human skeleton, called an endoskeleton, crustaceans have external skeletons, called exoskeletons. Exoskeletons are made up of chitin, a compound rich with calcium. This is similar to keratin, which comprises your nails and hair. Exoskeletons are tough, like armor, and relatively inelastic, so much like buying a new costume when you outgrow your old one, crustaceans must shed, or molt, their exoskeletons as they grow in a process scientists call ecdysis.

Ecdysis can be a pretty scary process to undergo. It is comparable to taking off your wetsuit without being able to use your hands! When an organism begins ecdysis, it enlarges the skin cells beneath its old exoskeleton and begins secreting calcium to form its new one. It then pumps in seawater to force the old exoskeleton away from its tissues, splitting it in half at the base of the carapace, or the upper body, and the tail, so it can escape. Now here comes the really scary part… In addition to shedding their outer covering, crustaceans must also shed their eye surfaces, throat and gut linings! Crustaceans have grinding teeth in their stomachs, called their gastric mill, that they use to break down their food. Since these grinding teeth are composed of chitin, the crustacean must shed them to grow a larger gastric mill for a larger stomach. It is possible during this tricky molting process to accidentally tear of an eye or a limb, or get stuck all together! How terrifying! Fortunately, crustaceans have the ability to regenerate, or regrow, their lost appendages just for this occasion. If a crustacean loses an eye, however, they must regenerate it quickly because the hormone that prevents them from molting continuously is distributed from a gland in their eye stalk. Without an eye, and without this hormone, crustaceans are unable to cease ecdysis and perform other normal body functions. Hurry, grow it back!

Escape from an old exoskeleton can take anywhere from several minutes to a half an hour, depending on the species, size, and environmental conditions. While escaping, clawed crustaceans must dehydrate and shrink their tissues enough to pull their whole claw through a hole the size of their wrist! Once all the way out, the crustacean swells with seawater, becoming up to 15% larger in size and 40-50% heavier in weight, only to release that seawater once it is done calcifying, or hardening, its new exoskeleton. This ensures that the newly molted crustacean has formed a larger exoskeleton and provided ample growing room for the future. Often, in order to speed up calcification, the crustacean eats its old exoskeleton to reabsorb some of the calcium it put into making its old armor. This may seem ghastly, but this way, the crustacean guarantees that it has enough calcium to generate its new exoskeleton.

While the crustacean hardens its armor in the next few hours after molting, it is too soft to defend itself against predators or other larger crustaceans. Newly molted lobsters are so rubbery and squishy that they are fondly referred to by fishermen as ‘jellies.’ To prevent a fight they cannot win, crustaceans tend to molt and calcify in the safety of their burrows, whether that be a hole in the sand or a deep crevice in the rocks.

With how spooky a process ecdysis can be, it is a good thing that crustaceans molt less with age as their growth slows. This is especially true for adult females, who naturally molt less because they cannot undergo ecdysis while they are laden with eggs. While an adult male lobster will molt once a year, an adult female lobster carrying eggs will molt once every two years. Regardless of sex, crustaceans grow slower, and therefore molt less, in colder waters. It is then safe to assume that crustaceans are always hoping for a colder Halloween!

Written By: Kathy Miller

The California Spiny Lobster

The California spiny lobster is a unique invertebrate (species lacking a backbone) that is found off the coast of southern California. This type of lobster belongs to a group of invertebrates known as Arthropoda. Arthropoda’s characteristics consist of having a segmented body, exoskeleton, and jointed appendages. These lobsters share the same grouping classification as insects and spiders! How cool is that!

California Spiny Lobster

A California spiny lobster hiding in its den.

The California spiny lobster lacks claws, unlike its friend, the American lobster, which can be found off the eastern coast. They are also reddish-brown in color and have an enlarged pair of antennae, used for sensing their environment. These antennae can also produce a loud clicking noise to warn off predators. California spiny lobster get their name from the forward-pointing spines that cover their bodies to help protect them from predators.

California Spiny Lobster tim

Credit: Tim S

Their hard shell, or exoskeleton, also helps to protect them from predators, but can make growing a challenge. To grow, the lobster must shed their shell to increase their size! This process is called molting. To do this the lobster must reduce the size of their body in the shell, by drawing in as much water as they can, so their shell isn’t too tight. Then, the shell breaks between the tail and their body (otherwise known as a carapace). The lobster will then flex their body back and forth and eventually back out of their old shell. During this period, the lobster is shell-less, and EXTREMELY vulnerable. They must stay hidden because it’s super hard to protect themselves from prey without their hard exoskeleton protecting them. The lobster will then start the process of growing a new shell, which can take several months.

California Spiny Lobster 2

CIMI snorkelers discover a discarded lobster molt in the water!

When it comes to movement in the water, these guys are experts! With ten legs, these lobsters can walk along the sea floor, as well as move backwards and even sideways! However, if they need to move fast from predators, they can tuck their tails under their abdomens and rapidly propel themselves backwards, similar to how octopus and squid move!

These animals are nocturnal, and spend most of their day hiding in rocky crevices. At night, they leave their dens in search of a meal. Their diet ranges from algae and dead organisms to snails, sea urchins, and clams. They have even been known for cannibalism in desperate times, and have been seen feasting on injured or recently molted lobsters!

Whether you see lobsters as an interesting sea creature or a delectable meal, next time you’re at your local supermarket or on a snorkel, be sure to check out everything these amazing creatures have to offer!

California Spiny Lobster hair

Lobsters make great head masseuses and hair stylists, when they’re not busy using their ten legs for scuttling about. Credit: Gabrielle R and Capri L

P.S. For some inspiration from a rabbi on growing through adversity and learning from lobster, click here: http://www.stillworks.org/blog/2016/2/27/how-to-grow-through-stress-lessons-from-a-lobster-by-a-rabbi

Written By: Brooke Fox








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