MORPHOLOGY OF THE GREEN TURTLE

Images courtesy of: From St. Catherine's Island Sea Turtle Conservation Program :A cast of a juvenile Cretaceous sea turtle, Toxochelys, whose carapace, usually from 2 to 4 feet long is only about 24 cm (9.5 inches) long. Triebold Paleontology, Inc and Articulated composite skeleton of Carolinochelys wilsoni displayed at the Science Museum of Minnesota. (Photograph courtesy of Science Museum of Minnesota).

Images courtesy of: This image (or other media file) is in the public domain because its copyright has expired. This applies to the United States, Canada, the European Union and those countries with a copyright term of life of the author plus 70 years.

I. EVOLUTION AND NATURAL HISTORY

 

The green turtle is a member of the family, Cheloniidae. As one of the oldest sea turtle species, it is the only species in the genus Chelonia. Its population extends throughout tropical and subtropical waters and forms two distinct groups in Atlantic and Pacific oceans. Green sea turtles are known for lengthy migration patterns between their feeding grounds and the location they were hatched from.

 

i. Life History

When green sea turtles are born they are carnviorous, yet as they mature to juveniles and adult turtles, they are commonly found in seagrass closer inshore as herbovorous grazers. As mature green sea turtles, female green sea turtles control mating, sometimes resulting in polyandry. When a gravid female is ready to lay her eggs, she looks for a suitable nesting site where she digs a hole with her hind flippers and then deposits a number of eggs in the nest. After 45 to 75 days, the eggs hatch at night and newly-emerged turtles instinctively head directly towards the waters' edge. (United States Fish and Wildlife Service). After their trek to the ocean, juvenile green sea turtles spend three to five years in the open ocean as carnivores (Reich 2007). Green sea turtles are known to live long lives, estimated at 80 years where they reach full maturity.

 

ii. Distribution

Image courtesy of: This image (or other media file) is in the public domain because its copyright has expired. This applies to the United States, Canada, the European Union and those countries with a copyright term of life of the author plus 70 years.

 

The green sea turtle population consists of two distinct subpopulations, an Atlantic subpopulation and an Indo-Pacific population. Each population is genetically-distinct, whose range and feeding behaviors are unique to that population.

a. Atlantic subpopulation

The Atlantic subpopulation ranges from "as fas north as Canada in the Western Atlantic and the British Isles in the east to as far south as the southern tip of Africa in the east and Argentina in the Western Atlantic." (Wikipedia). Its major nesting sites are scattered throughout the Caribbean, along the eastern United States, the eastern coast of the South American continent, and isolated islands in the South Atlantic.(Wikipedia).

b. Indo-Pacific subpopulation

The Indo-Pacific subpopulation ranges from "as far north as the southern coast of Alsaka and as far south as Chile in the east. In the Western Pacific, the population is known as far north as Japan and even southern parts of Russia's Pacific coast and as far south as the northern tip of New Zealand and a few islands further south of Tasmania. The turtles can be found throughout the entire range of the Indian Ocean" (Caribbean Conservation Corporation). Their nesting grounds are scattered throughout the region. Nesting grounds are found in the Hawaiian Islands, Mexico, the South Pacific, the northern coast of Australia and Southeast Asia. In the Indian Ocean, major nesting colonies have been found in India, Pakistan, and other countries in that region (Dobbs, 2007).

II.. ANATOMY AND MORPHOLOGY

Chelonia mydas, is commonly known as the green sea turtle. It has a "dorsoventrally-flattened body, a beaked head at the end of a short neck, and paddle-like arms well-adapted for swimming."(United States Fish and Wildlife Service). The proper name for the green sea turtle shell is carapace. The carapace of the turtle, as illustrated below, displays various color patterns, providing the distinction of a species. At birth, green sea turtle hatchlings have black carapaces. As adults, their carapaces are either entirely brown, spotted, or marble with variegated rays.

III. SKELETAL ANATOMY

Image courtesy of: From St. Catherine's Island Sea Turtle Conservation Program (Science Museum of Minnesota).

The skeleton is made up of bones and cartilages. The skeleton is divided into three main parts: the skull, the axial skeleton, and the appendicular skeleton. In sea turtles, each of these bony groups is a composite of several structures. The skull includes the braincase, jaws, and hyoid apparatus. (Wyneken,2001). The axial skeleton is cmoposed of the carapace, vertebrae, and tibs, and the derivatives of the ribs. (Wyneken, 2001). The plastron is a composite including derivatives of the axial and appendicular skeleton (ventral ribs plus shoulder elements). The appendicular skeleton includes the flippers, hind lims, and their supporting structures (the pectoral and pelvic girdles ) (Wyneken, 2001). The skeletal system of Chelonia mydas, provides the frame for work for other physiological system just as in humans.

i. Carapace

Image courtesy of: Wikimedia Commons

The carapace is essentially the shell of the green sea turtle. It is composed of bone covered by keratinous scutes or blubber. The margins of cheloniid scutes and the bones' sutures do not align with one another. (Wyneken, 2001).

 

ii. Plaston

The plastron is the ventral or under side of of the green sea turtle shell. "The plastron is composed of four pairs of bones (from anterior to posterior: epiplastron, hyoplastron, hypoplastron, and xiphiplastron) and one unpaired bone (entoplastron)" (Wyneken, 2001).

 

IV. CIRCULATION ANATOMY

The circulatory system consists of the heart, arteries, veins, and lymphatic vessels. The heart is multichambered and serves as the main pump. Arteries are composed of thick walls made uup of muscle and elastic fibers; arteries carry blood to the heart. The veins contain valves, moving blood away from the heart. The lymphatic vessels trtansport tissue fluid from outside th circulatory system back to the blood, surrounding the arteries and veins like sheaths (Wyneken, 2001)

 

i. Heart

The turtle heart contains four chambers: a sinus venosus, two large atria, and a ventricle. The ventricle is subdivided into three cmopartments: the cavum venosum, cavum arteriosum, and the cavum pulmonae (Wyneken, 2001).

ii. Arteries

The arteries consist of two great vessels: two aortas and a pulmonary trunk. "The right aorta supplis bloos to the head, limbs, and lower body, the left aorta to the viscera" (Wyneken, 2001). The pulmonary trunk is divided into the right and left pulmonary arteried, which provides blood to the left and right lungs.

V. LUNG AND AIRWAY ANATOMY

The lungs and airways comprise the pulmonary system in the turtle. The pulmonary system is composed of the glottis, trachea, a bronchus to each lung, and the left and right lungs (Wyneken, 2001). The sea turtle has multichambered lungs, consisting of multiple lobes. "Ventilation of the lungs occurs without the assistance of a diaphragm" (Wyneken, 2001).They ventilate by utilizing the ventral muscles of their pelvic and pectoral girdles, in order to change the pressure within the pleuroperitoneal cavity (Wyneken, 2001). Thus, turtles breath-hold, so that blood oxygen levels lower considerably.

 

 

 

This project was created as a part of a class project in the Animal Physiology class in the Department of Biology at Davidson College

E-mail questions to: snreid@davidson.edu

 

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