question: How does a turtle’s shell grow while the turtle grows? What is it made of?
comment: The shell is made up of panel-like things called scutes. With most types of turtles, these scutes shed periodically to allow bigger scutes to form. They are made out of keratin - same as human hair & nails. Source: I’m a turtle fan.
passages: Section::::Anatomy and morphology.:Skin and molting.
   Section::::Paragonimus.
   Section::::Formation.:Development.
   Section::::Geological explanation.:Formation by regeneration.
   Section::::Economic importance.
   The shell is added to, and increases in size, in two ways—by increments added to the open edge of the shell, and by a gradual thickening throughout the animal's life.
   Section::::Ecology and life history.
   Sea turtles lay their eggs on dry, sandy beaches. Immature sea turtles are not cared for by the adults. Turtles can take many years to reach breeding age, and in many cases, breed every few years rather than annually.
  
  Researchers have recently discovered a turtle's organs do not gradually break down or become less efficient over time, unlike most other animals. It was found that the liver, lungs, and kidneys of a centenarian turtle are virtually indistinguishable from those of its immature counterpart. This has inspired genetic researchers to begin examining the turtle genome for longevity genes.
   A group of turtles is known as a bale.
  
  Section::::Ecology and life history.:Diet.
  
  A turtle's diet varies greatly depending on the environment in which it lives. Adult turtles typically eat aquatic plants; invertebrates such as insects, snails, and worms; and have been reported to occasionally eat dead marine animals. Several small freshwater species are carnivorous, eating small fish and a wide range of aquatic life. However, protein is essential to turtle growth and juvenile turtles are purely carnivorous.
   The organic pellicule is found in most polyplacophora (but not 'basal' chitons, such as "Hanleya") but is unusual in aplacophora. Developmentally, sclerite-secreting cells arise from pretrochal and postrochal cells: the 1a, 1d, 2a, 2c, 3c and 3d cells. The shell plates arise primarily from the 2d micromere, although 2a, 2b, 2c and sometimes 3c cells also participate in its secretion.
  
  Section::::Morphology.:Internal anatomy.
   Section::::Biodiversity.
   Shells can grow holoperipherally, where new material is added all around the margin, or mixoperipherally, where new material is added to the posterior region of the shell in an anterior direction, growing towards the other shell.
  
  Section::::Description.:Mantle.
   Between each of the pleurals are a series of neural bones, which although always present are not always visible, in many species of Pleurodire they are submerged below the pleurals. Beneath the neural bone is the Neural arch which forms the upper half of the encasement for the spinal chord. Below this the rest of the vertebral column. Some species of turtles have some extra bones called mesoplastra, which are located between the carapace and plastron in the bridge area. They are present in most Pelomedusid turtles.
   In Scott Snyder's "Justice League" series, the Turtle is revised as believing in an opposing energy to the Speed Force, known as the "Still Force". Each time he accessed this power, it aged him. Now a hatchling (described as "The Fourth Generation of his line"), he is finally attuned to the Still Force, and grants Gorilla Grodd (now a member of Luthor's Legion of Doom) total control of it to combat the Flash.
  
  Section::::Powers and abilities.
   BULLET::::- Yucatán box turtle, "Terrapene yucatana"
  
  Box turtles have diploid somatic cells with 50 chromosomes.
  
  Section::::Ecology and behavior.
  
  Section::::Ecology and behavior.:Life cycle and predation.
   Section::::Construction.
   The length of the type specimen's shell is 120 mm, its breadth 83 mm and its depth 45 mm. Females are slightly larger than males, but this smallish turtle does not seem to exceed about 13 cm in carapace length even when fully grown.
  
  Section::::Ecology.
   Section::::Ecology and behavior.:Life cycle.
   Once the larval bivalve settles and becomes a juvenile, the rest of the shell starts to grow. The earliest part of the shell that formed often shows in the adult shell as a protruding area known as the umbo, at the tip of which is the prodissoconch, assuming it has not been eroded or obscured in some other way. Quite often there is a visible line of demarkation where the prodissoconch ends and the umbo begins, and there may be a sudden appearance of sculpture at that point.
  
  Section::::Larval stages.
   Section::::Relationship to turtles.
   The evolution of the plastron has remained more mysterious, though Georges Cuvier, a French naturalist and zoologist in the 19th century, wrote that the plastron developed primarily from the sternum of the turtle. This fits well with the knowledge obtained through embryological studies, showing that changes in the pathways of rib development often result in malformation or loss of the plastron. This phenomenon occurs in turtle development, but instead of experiencing complete loss of the sternum the turtle body plan repurposes the bone into the form of the plastron.
   Although its evolutionary history—what the forerunner to the species was and how the close relatives branched off—is not well understood, the painted turtle is common in the fossil record. The oldest samples, found in Nebraska, date to about 15 million years ago. Fossils from 15 million to about 5 million years ago are restricted to the Nebraska-Kansas area, but more recent fossils are gradually more widely distributed. Fossils newer than 300,000 years old are found in almost all the United States and southern Canada.
  
  Section::::Taxonomy and evolution.:DNA.
   Section::::Definition and description.
  
  The Pleurodira are identified by the method with which they withdraw their heads into their shells. In these turtles, the neck is bent in the horizontal plane, drawing the head into a space in front of one of the front legs. A larger overhang of the carapace helps to protect the neck, which remains partially exposed after retraction. This differs from the method employed by a cryptodiran, which tucks its head and neck between its forelegs, within the shell.
   Section::::Replicas.
   One of the most prized shell publications of the 19th century, a series of books titled " (published by the French naturalist Jean-Charles Chenu from 1842 to 1853), contains illustrations of both adult and juvenile "L. gigas" shells and one uncoloured drawing depicting some of the animal's soft parts. Almost forty years later, a colored illustration from the "Manual of Conchology" (published in 1885 by the American malacologist George Washington Tryon) shows a dorsal view of a small juvenile shell with its typical brown and white patterning.
  
  Section::::Anatomy.:Soft parts.
  