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Sea Turtle Body Parts and Functions
With very few adaptations, the fusiform shape and skeletal structure of sea turtles has served them well ever since they lived alongside dinosaurs 100 million years ago.
A hard shell helps to protect them from modern day predators and they use elongated paddle-shaped front flippers for movement and for diving deep into the ocean.
The 4 Key Stages in the Lives of Sea Turtles
Some funny scientific fish names used in species identification also help to describe anatomies.
Hence, the physical characteristics of the sea turtle refer to the internal and external skeleton, major organs, muscular system, and limbs.
Still, several other unique features about sea turtle anatomy include:
- Size helps to regulate body temperature, especially the leatherback sea turtle (Dermochelys coriacea).
- They can also excrete excess salt from special glands near their eyes.
In simplified marine biology terms, there are four (4) major stages in the fascinating process of birth to maturity in sea turtle development and life cycle.
Sea Turtle Egg Stage
The egg stage begins when a female sea turtle exits the water to lay her eggs inside a nest on a sandy beach. She uses her pelvic flippers (hindlimbs) to dig a large chamber. The eggs are spherical in shape with a soft outer shell.
In fact, the average clutch size for these enormous marine reptiles varies according to the different species of sea turtle (but typically between 50 and 200 eggs).
Next, a period of incubation that allows the embryos to develop inside the egg chamber may last for several weeks (45 to 70 days).
By and large, the brooding period depends on the species and the environmental conditions (e.g. air temperature).
Pro Tip: The temperature also influences the gender of baby sea turtles when they hatch (warmer for females and cooler for males).
Sea Turtle Hatchling Stage
Immediately after the tiny sea turtles have hatched (less that 2 inches long), they emerge from the nest and head to the sea.
Within a few hours, using the darkness for extra protection, they crawl along the sand and head for the ocean to swim offshore - using the reflection of moonlight on the water for directional guidance.
Sea Turtle Juvenile Stage
Having reached the ocean, and many of them fail to do so, turtle hatchlings swim almost non-stop for up to 48 hours trying to reach the "relative" safety of deep water.
Here's the thing:
Many years ago, this particular phase in sea turtles was referred to as the "lost years" because it was difficult to determine their exact whereabouts.
Drifting with ocean currents, the juveniles will search for sargassum seaweed for food and nutrients.
During this stage, which may last for several years, the carapace (outer shell) begins to harden, the flippers start to get stronger, and the beak makes some adaptations to better suit their diet (e.g. omnivorous or herbivorous).
Sea Turtle Adult Stage
Adult sea turtles tend to reach sexual maturity after the age of seven (older in other species). This is when they undertake the long journey back to familiar coastal waters and nesting beaches to continue the life cycle.
Interesting Fact: The average lifespan for sea turtles is about fifty (50) years and up to one hundred (100) years in some of the least endangered species.
Anatomy Facts about Sea Turtles
There are only seven sea turtle species (order Testudines) still in existence today. They are all marine reptiles that need air to breathe, but they spend almost all of their lives swimming in different oceans around the world.
This segment explains more about sea turtle body parts and how their unique anatomy has adapted over the years for life in the sea and on land.
Shell (Carapace) and Skeleton
The shell of a sea turtle is made of ribs and bones fused together and forms part of the exoskeleton. There are two parts to the outer shell - the upper dorsal section and the lower ventral section.
The upper section (the carapace) is hard and quite bony. Whereas, the bottom part (the plastron) helps to protect the turtle's pelvic girdle and underbelly.
With the exclusion of leatherback sea turtles, which have dorsal ridges running longitudinally on the top, the upper shell contains a number of segmented lateral plates (also called scutes).
But wait - there's more:
They also have marginal scutes that run along the edge of the carapace made of keratin, a material similar to that in human fingernails.
Because different species display contrasting scute patterns, scientists can use these dissimilar configurations as an aid in species identification.
All sea turtles have a flattish, hydrodynamic, torpedo-shaped body that helps to reduce drag when they swim in water. As a result, they are efficient swimmers.
Fun Fact: One of the key differences between land turtles and sea turtles is that the marine reptile cannot protect itself by retracting the head and limbs into the shell.
Forelimbs and Hindlimbs
Sea turtles don't have "feet". Instead, they have two modified (elongated) forelimbs, and two shorter hind limbs at the back (called flippers).
The front flippers are long and very powerful. They use them like paddles for short bursts of propulsion, such as when they need to swim fast or deep to escape their natural predators (e.g. sharks and groupers).
Whereas, the two flippers at the back of the shell are used more for steering and for digging nest chambers in the sand.
Plus, male sea turtles have a longer tail than the females, and the single cloacal opening is nearer the tip (used for releasing waste products). Males also have larger claws on the front flippers, used mostly for gripping the females during the mating process.
Internal Organs and Respiration
The heart of a sea turtle has three chambers, with two atria and one ventricle. Some adaptations in the digestive system means most of the species are well adapted to eating seaweed, jellyfish, and small marine animals.
Having the lungs (not gills) positioned close to the top of the body means it's easier to breathe air for respiration when they rise to the surface.
In case you were wondering...
In addition, when resting underwater sea turtles can stay submerged for several hours (up to 7) before they need to breathe. An extremely slow heart rate, and being able to store oxygen in their muscles and blood, helps them conserve oxygen (often making a single beat every nine minutes).
Head Skull and Tomium Beak
The number of prefrontal scales located between the large eyes and eyelids help to differentiate the species. So for example, the green sea turtle (Chelonia mydas) has a single pair.
Instead of teeth, sea turtles have a sharp, horny beak-like structure used for grazing on seagrasses or cutting sea sponges and coral heads.
As a consequence of that...
The diet determines the actual shape of the beak and how it's used. Thus, the powerful jaws of the loggerhead sea turtle (Caretta caretta) can easily crush small aquatic crustaceans.
Following some adaptations, leatherback turtles have backward-pointing spines inside the throat. This modification means they can easily swallow poisonous jellyfish species, such as the Portuguese man-of-war and not get stung.
Brain and Sensory Organs
Despite having excellent vision underwater, sea turtles actually struggle to identify objects on dry land. But, being able to detect the Earth's magnetic field means they can pick up chemical cues and use them for navigation when migrating across huge oceans.
Sea turtles do not have ears in the normal sense. But, they are able to detect low-frequency vibrations and sounds underwater.
Pro Tip: The leathery turtle is the heaviest of all weighing up to five hundred (500) kilograms. Fully grown adults can also measure almost three (3) metres in length (flipper to flipper).