The Anatomy of a Lobster: Understanding the Different Parts of a Lobster

External Anatomy:

Exoskeleton

The anatomy of a lobster includes its exoskeleton, a hard outer shell made primarily of chitin, serving as a form of armour that shields the lobster from predators and environmental threats. This exoskeleton is a crucial feature for protection, but it does not grow with the lobster. As lobsters grow, they must shed or moult their exoskeletons in a process called ecdysis.

Moulting allows the lobster to form a new, larger shell underneath the old one, giving it room to expand. During this vulnerable period, the lobster remains soft until the new exoskeleton hardens, making it more susceptible to predation.

Claws (Chelae)

Lobsters are well known for their two large claws, each serving different purposes. The larger of the two is known as the crusher claw, which is thick and strong, designed to crush the shells of prey like crabs and molluscs. The other claw, known as the pincher claw or cutter claw, is smaller, more slender, and equipped for grabbing, holding, and tearing apart prey. These claws are essential for both hunting and defence, and each is adapted to perform specific tasks, showcasing the lobster’s complex hunting techniques.

Antennae

The lobster's antennae play a crucial role in sensing its surroundings. These long, slender appendages are highly sensitive to touch and chemical signals in the water, helping the lobster detect nearby food, mates, or potential threats. Lobsters have two pairs of antennae: the long pair, which is primarily used for sensing distant stimuli, and a shorter, more tactile pair, which assists in navigating close objects. The antennae are essential for the lobster's ability to interact with its environment and navigate its often complex underwater world.

Rostrum

The rostrum is a sharp, forward-pointing extension of the carapace located between the lobster's eyes. Its primary function is to protect the sensitive areas of the lobster’s body, specifically the eyes and brain. Acting as a natural shield, the rostrum helps the lobster avoid injury while navigating its surroundings, particularly in rocky crevices or while foraging on the ocean floor.

Eyes

Lobsters have compound eyes, which are made up of thousands of tiny lenses called ommatidia. These eyes are adept at detecting movement and changes in light intensity, though lobsters do not have sharp, detailed vision. Instead, their eyes are more sensitive to motion, which is advantageous for spotting predators or prey. Despite living in often murky environments, lobsters' vision is highly adapted to the low light conditions of the deep sea.

Legs and Swimmerets

Lobsters have five pairs of walking legs, with the first pair modified into claws. The remaining legs are used for walking along the seafloor, allowing the lobster to move efficiently in search of food. Additionally, lobsters possess swimmerets, smaller appendages located on the underside of the abdomen. These swimmerets play a vital role in reproduction and mobility, particularly for female lobsters, as they use them to carry eggs. Swimmerets also assist in helping lobsters swim backwards quickly, enabling them to evade predators.

Internal Anatomy:

Gills

Lobsters breathe underwater through gills, which are located beneath the carapace on either side of their body, attached to the base of the walking legs. These feathery structures extract oxygen from water as it flows through them. The gills are highly efficient at absorbing dissolved oxygen while releasing carbon dioxide back into the water. For optimal respiration, lobsters pump water across their gills by moving their legs and beating their swimmerets, ensuring a continuous flow of oxygenated water even when they are stationary.

Digestive System

The lobster's digestive system is a complex network designed for breaking down its varied diet of fish, molluscs, and plant matter. Food enters the stomach, located in the lobster's head, where it encounters a specialised structure called the gastric mill. This mill contains small, tooth-like structures that grind the food into smaller particles. After being processed in the gastric mill, the food moves through the intestine, which extends along the length of the lobster’s body, absorbing nutrients. 

The digestion process is assisted by the hepatopancreas, commonly known as the tomalley, which functions like the liver and pancreas in other animals. The hepatopancreas produces digestive enzymes and stores nutrients, playing a vital role in both digestion and metabolism.

Circulatory System

Lobsters have an open circulatory system, meaning that instead of blood flowing through closed vessels as in humans, it is pumped into cavities, where it bathes the organs directly. Lobster blood, or hemolymph, is blue due to the presence of copper-based hemocyanin, which binds to oxygen. The lobster's heart, located just above the stomach, pumps hemolymph through the body. The open system allows the hemolymph to move freely, delivering oxygen and nutrients to tissues before it is collected and recirculated.

Nervous System

The lobster’s nervous system is relatively simple compared to mammals but highly specialised for its needs. It consists of a brain, located in the head, and a ventral nerve cord that runs the length of the body. Instead of a centralised brain, lobsters have a ganglion-based system, meaning that much of their nervous function is decentralised, allowing for local control over movement and sensory processing. This structure helps lobsters react quickly to stimuli, coordinating complex behaviours like hunting, defence, and locomotion. Despite having no cerebral cortex, which is responsible for higher reasoning in humans, lobsters are highly adept at responding to their environment and making survival decisions.

Each part of the lobster's internal anatomy works harmoniously to support its life in the ocean, from breathing and digestion to movement and sensory responses. This internal design ensures that lobsters remain well adapted to their roles as both predator and prey in marine ecosystems.

Culinary Relevance:

Lobsters are prized in the culinary world for their sweet, tender meat, with different parts of the lobster offering unique textures and flavours. The claws, tail, and tomalley are the most commonly used parts in cooking, each valued for their specific qualities and unique look in the lobster’s anatomy. 

Claws

The claws are a favourite for many due to their soft, succulent meat. The crusher claw tends to have meat with a firmer texture, while the pincher claw offers slightly more tender meat. Claw meat is often used in dishes like lobster rolls or as a garnish for salads and pasta. Because of its delicacy, it is also ideal for dipping in delicious hot butter or served with light seasonings to highlight its natural sweetness.

Tail

The lobster tail is considered the most desirable part, prized for its dense, meaty texture. It is often served as the centrepiece of a lobster dish, either grilled, steamed, or baked. The tail meat is more fibrous than claw meat, making it ideal for rich sauces or stuffing, as it holds its structure well. Lobster tails are commonly used in succulent surf and turf dishes or simply paired with garlic butter for a classic presentation.

Tomalley

The tomalley, or hepatopancreas, is a green, paste-like substance found in the lobster's body cavity. It has a strong, rich flavour, similar to that of crab or shrimp roe. While considered a delicacy by some, the tomalley can be polarizing due to its intensity. It is sometimes used in sauces or bisques to add depth of flavour. However, due to potential contaminants absorbed by the lobster from its environment, some health advisories suggest consuming the tomalley in moderation.

Cracking Open and Eating a Lobster

Eating a lobster can be a bit of an adventure, requiring some skill to access all the edible parts. Below are some tips for cracking and enjoying lobster safely:

1. Claws: Start by removing the claws from the body. Use a nutcracker or lobster cracker to break open the shell. Once cracked, pull out the tender meat using a lobster pick or fork. Be sure to check the knuckles, as they also contain meat.

2. Tail: Twist the tail away from the body, then use your hands or a lobster cracker to break open the shell along its length. Gently pull out the tail meat in one piece. You can also remove the digestive vein that runs through the tail, which is typically discarded.

3. Body: The body of the lobster contains small pockets of meat, especially in the area between the legs. Although less meaty than the claws or tail, some lobster enthusiasts enjoy picking through the body for these morsels. The body is also where you’ll find the tomalley.

4. Swimmerets and Legs: Lobster legs and swimmerets contain small amounts of meat. You can extract the meat by breaking off the legs and using your teeth to squeeze the meat out, or by rolling a small rolling pin over them.

Edible vs. Discarded Parts

• Edible parts: The meat from the claws, tail, knuckles, and legs; tomalley (optional, depending on preference).

• Discarded parts: The shell, digestive tract (vein), and gills, as well as any uneaten internal organs like the stomach.

Lobster Behavior and Adaptations:

Lobsters have evolved a variety of fascinating behaviours and anatomical adaptations that help them survive and thrive in their underwater environments. Their anatomy is finely tuned to support crucial activities such as hunting, mating, and defence, all while navigating the often rocky and unpredictable ocean floor.

Hunting and Feeding

Lobsters are primarily nocturnal hunters, using their strong claws and sensory systems to find and capture prey. The combination of the crusher claw and pincher claw allows lobsters to be versatile in their diet. The crusher claw is used to break the hard shells of prey such as clams, crabs, and snails, while the pincher claw helps grasp and tear softer prey. Their antennae and tiny sensory hairs, called setae, scattered across their bodies help lobsters detect chemical signals in the water, guiding them to food sources even in murky or dark waters.

The rostrum offers protection during foraging, shielding their sensitive eyes and brain from sharp objects or other predators. Additionally, the lobster’s ability to move both forwards and backwards, using their legs for walking and their swimmerets for swimming, gives them agility in pursuing prey and escaping danger.

Mating and Reproduction

During mating, lobsters demonstrate complex social behaviours, with males engaging in battles to win the right to mate with females. Their size and claw strength often determine the outcome of these competitions. Females, once they have selected a mate, moult to allow mating to take place. Lobsters exhibit internal fertilisation, and the female carries the fertilised eggs on her swimmerets until they are ready to hatch. These swimmerets also aid in ventilation, providing the eggs with oxygen, which is vital for the developing embryos.

Females use their powerful swimmerets to fan water over the eggs, ensuring they stay clean and well-oxygenated during their incubation. 

Defending Themselves

Lobsters are well equipped to defend themselves from predators, relying on their hard exoskeleton and formidable claws as their first line of defence. The thick carapace acts as armour, protecting the lobster’s soft tissues. If threatened, a lobster will raise its claws in a defensive posture, using its crusher claw to deliver powerful blows that can deter even large predators.

Lobsters also have an impressive ability to regenerate lost limbs, such as claws or legs, allowing them to recover from predatory attacks or injuries sustained during fights with other lobsters. This regeneration ability is a critical adaptation that helps lobsters survive life on the ocean floor.

Camouflage and Burrowing

Lobsters use camouflage to blend into their rocky and sandy environments. Their dark, often mottled shells allow them to remain hidden from predators like larger fish or seals. They also use their powerful legs to dig burrows or hide in crevices, providing them with a secure refuge during moulting periods when they are particularly vulnerable due to their soft exoskeleton.

Adaptations for Extreme Conditions

Lobsters are highly adaptable to a variety of marine environments, from shallow waters to depths of up to 500 meters. They have evolved to thrive in both warm and cold waters, with some species even capable of surviving in low oxygen environments by slowing their metabolism. One of the most remarkable adaptations is their long lifespan and ability to continually grow through moulting.

Lobsters can live for decades, and unlike many animals, they do not show typical signs of ageing, a trait that has intrigued scientists studying ageing and longevity.