What do Turtles Eat
Turtles are diapsids of the particular order Testudines (or Chelonii) seen as a a special bony or cartilaginous shell developed from their ribs plus acting as a protect. "Turtle" may refer to the order as the whole (American English) or to fresh-water and sea-dwelling testudines (British English). The particular order Testudines includes each extant (living) and extinct species. The earliest identified members of this team date from 220 million years ago, making turtles one of the earliest reptile groups and the more ancient group than snakes or crocodilians. Associated with the 356 known species alive today, some are usually highly endangered.
Turtles are usually ectotherms—animals commonly called cold-blooded—meaning that their internal temp varies according to the particular ambient environment. However, due to the fact of their high metabolic rate, leatherback sea turtles have a body temperature that is noticeably increased than that of the surrounding water. Turtles are usually classified as amniotes, along with other reptiles, birds, and mammals. Like additional amniotes, turtles breathe air and do not place eggs underwater, although many species live in or even around water. The study of turtles is called cheloniology, after the Greek term for turtle. It will be also sometimes called testudinology, after the Latin name for turtles.
Differences exist in usage of the common terms turtle, tortoise, and terrapin, based on the variety of English being used. These terms are typical names and do not reflect precise biological or taxonomic distinctions.
Turtle may either relate to the order since a whole, or to particular turtles that create up a form taxon which is not monophyletic, or might be restricted to only aquatic species. Tortoise usually refers to any land-dwelling, non-swimming chelonian. Terrapin can be used to describe several species of small, edible, hard-shell turtles, typically those found in brackish waters.
In Northern America, all chelonians are usually commonly called turtles. Tortoise is used only within reference to fully terrestrial turtles or, more narrowly, only those members of Testudinidae, the family of modern property tortoises. Terrapin may relate to small semi-aquatic turtles that live in new and brackish water, in particular the diamondback terrapin (Malaclemys terrapin). Although the people of the genus Terrapene live mostly on land, they will are known as box turtles rather than tortoises. The particular American Society of Ichthyologists and Herpetologists uses "turtle" to describe all types of the order Testudines, regardless of whether they are land-dwelling or sea-dwelling, and uses "tortoise" as a more specific expression for slow-moving terrestrial species.
In the United Empire, the term turtle is utilized for water-dwelling species, including ones known in the US as terrapins, although not for terrestrial species, which are known only as tortoises.
Rangking: 51
Size: 149.4KB
Width: 1280
Height: 857
pictures: top 10 animal, top ten beautiful animal
The word chelonian will be popular among veterinarians, scientists, plus conservationists working with these animals being a catch-all title for any person in the particular superorder Chelonia, which includes just about all turtles living and vanished, as well as their immediate ancestors. Chelonia will be based on the Ancient greek word for turtles, χελώνη chelone; Greek χέλυς chelys "tortoise" is also used in the formation of scientific names of chelonians. Testudines, on the other hand, is based on the particular Latin word for tortoise, testudo. Terrapin comes from an Algonquian word for turtle.
Some languages perform not have this variation, as all of these are referred to by the particular same name. For instance , in Spanish, the word tortuga is used for turtles, tortoises, and terrapins. A sea-dwelling turtle is tortuga marina, a freshwater varieties tortuga de río, plus a tortoise tortuga terrestre.
The largest living chelonian is the leatherback ocean turtle (Dermochelys coriacea), which reaches a shell length of 200 cm (6. six ft) and can reach a weight of over 900 kg (2, 500 lb). Freshwater turtles are generally smaller, but along with the largest species, the Asian softshell turtle Pelochelys cantorii, a few people have been reported upward to 200 cm (6. 6 ft). This dwarfs even the better-known alligator snapping turtle, the largest chelonian in North The united states, which attains a shell length of up in order to 80 cm (2. 6 ft) and weighs since much as 113. 4 kg (250 lb).
Huge tortoises of the genera Geochelone, Meiolania, and other people were relatively widely dispersed all over the world into prehistoric times, and they are known to have existed in North plus South America, Australia, plus Africa. They became vanished at the same time as the appearance of man, and it will be assumed humans hunted all of them for food. The only surviving giant tortoises are on the Seychelles plus Galápagos Islands and can grow to over 130 centimeter (51 in) in duration, and weigh about 300 kg (660 lb).
The particular largest ever chelonian had been Archelon ischyros, a Late Cretaceous sea turtle recognized to have been as much as 4. 6 m (15 ft) long.
Sea Turtles Protection Guidelines
The smallest turtle is the speckled padloper tortoise of South Africa. It measures no more than 8 centimeter (3. 1 in) long and weighs about 140 g (4. 9 oz). Two other species associated with small turtles are the American mud turtles plus musk turtles that reside in an area that ranges from Canada to South America. The cover duration of many species in this group is much less than 13 cm (5. 1 in) long.
Turtles are divided into 2 groups, according to the way they retract their necks into their shells (something the our ancestors Proganochelys could not do). The mechanism of throat retraction differs phylogenetically: the particular suborder Pleurodira retracts laterally aside, anterior to shoulder girdles, while the suborder Cryptodira retracts straight back, between shoulder girdles. These types of motions are largely because of to the morphology and arrangement of cervical backbone. Of all recent turtles, the cervical column consists of nine joints and eight vertebrae, which are usually individually independent. Since these types of vertebrae are not fused and are rounded, the neck is more versatile, being able to bend in the backwards plus sideways directions. The major function and evolutionary inference of neck retraction is usually thought to be regarding feeding rather than safety. Neck retraction and reciprocal extension allows the turtle to reach out further to capture prey while going swimming. Neck expansion creates suction once the head is drive forward and the oropharynx is expanded, and this morphology suggests the retraction function is for nourishing purposes as the suction helps catch prey. The particular protection the shell provides the head when this is retracted is as a result not the main function of retraction, thus is an exaptation. As with regard to the difference between the two methods of retraction, both Pleurodirans and Cryptodirans use the quick extension of the neck being a method of predation, therefore the difference in retraction mechanism is not really due in order to a difference in ecological niche.
Head
Most turtles that spend most of their lives on property have their eyes looking lower at objects in front side of them. Some marine turtles, such as nipping turtles and soft-shelled turtles, have eyes closer in order to the very best of the mind. These species of turtle may hide from predators within shallow water, where they lie entirely submerged other than for their eyes plus nostrils. Near their eyes, sea turtles possess intrigue that produce salty tears that rid their body associated with excess salt taken in from the water they drink.
Turtles have rigid beaks and use their jaws to cut and munch food. Instead of having teeth, that they appear in order to have lost about 150-200 million years ago, the upper and lower teeth of the turtle are usually covered by horny side rails. Carnivorous turtles usually possess knife-sharp ridges for cutting through their prey. Herbivorous turtles have serrated-edged ridges that help them cut through tough plants. They will use their tongues to swallow food, but as opposed to most reptiles, they cannot stay out their tongues in order to catch food.
ShellPrimary article: Turtle shellTop of the shell of the turtle is called the carapace. The lower shell that encases the belly is known as the plastron. The carapace and plastron are joined up with together on the turtle's sides by bony buildings called bridges. The internal layer of a turtle's shell is made up of about 60 bones that include portions of the backbone and the ribs, meaning the turtle cannot crawl out of its shell. In most turtles, the outer layer of the shell is covered by horny scales called scutes which are part of its outer skin, or skin. Scutes are made up of the particular fibrous protein keratin that will also makes up the particular scales of other lizards. These scutes overlap the particular seams between the shell bones and add power to the shell. Some turtles don’t have horny scutes; with regard to example, the leatherback ocean turtle and the soft-shelled turtles have shells covered with leathery skin instead.
The shape of the shell gives helpful clues about how a turtle lives. Many tortoises have a big, dome-shaped shell that can make it difficult for predators to crush the covering between their jaws. One of the few exclusions is the African hot cake tortoise, which has a flat, flexible shell that allows it to hide in rock crevices. The majority of aquatic turtles have smooth, streamlined shells, which aid within swimming and diving. United states snapping turtles and musk turtles have small, cross-shaped plastrons that give all of them more efficient leg movement for walking along the particular bottom of ponds plus streams. Another exception will be the Belawan Turtle (Cirebon, West Java), which has sunken-back soft-shell.
The color of the turtle's shell may differ. Shells are commonly colored brown, black, or olive green. In some species, covers may have red, orange, yellow, or grey marks, often spots, lines, or even irregular blotches. One of the most colorful turtles is the far eastern painted turtle, which includes a yellow plastron and a black or olive shell with red marks around the rim.
Tortoises, being land-based, have rather heavy shells. In comparison, aquatic and soft-shelled turtles have lighter shells that will help them avoid sinking in water and go swimming faster with more agility. These lighter shells possess large spaces called fontanelles between the shell bones. The shells of leatherback sea turtles are extremely gentle because they lack scutes and contain many fontanelles.
It has been suggested by Jackson (2002) that the turtle shell can function as pH buffer. To endure through anoxic conditions, such as winter season periods trapped beneath glaciers or within anoxic dirt at the end of ponds, turtles utilize two general physiological mechanisms. In the situation of prolonged periods associated with anoxia, it has already been shown that this turtle shell both releases carbonate buffers and uptakes lactic acidity.
Great Barrier Reef Tours Cairns Best Value New Reef Tour Snorkel Dive 2 Reef Locations
Respiration Turtles
Respiration, for many amniotes, is achieved by the contraction and relaxation of specific muscles (i. electronic. intercostals, abdominal muscles, and/or the diaphragm) attached to an inner rib-cage that can broaden or contract the body wall thus assisting airflow out and in of the lung area. The ribs of Chelonians, however, are fused with their carapace and exterior to their pelvic plus pectoral girdles, a function unique among turtles. This particular rigid shell is not really capable of expansion, and by rendering their rib-cage immobile, Testudines have had to evolve special adaptations for respiration.
Turtle pulmonary ventilation occurs by making use of specific groups of abdominal muscles attached to their viscera and shell that pull the lungs ventrally throughout inspiration, where air will be drawn in via a negative pressure gradient (Boyle's Law). In expiration, the contraction of the transversus abdominis is the driving pressure by propelling the viscera into the lungs plus expelling air under optimistic pressure. Conversely, the calming and flattening of the particular oblique abdominis muscle pulls the transversus back lower which, once more, draws air flow back into the lungs. Important auxiliary muscles utilized for ventilatory processes would be the pectoralis, which is utilized in conjunction with the particular transverse abdominis during inspiration, and the serratus, which movements with the abdominal oblique accompanying expiration.
The lungs associated with Testudines are multi-chambered and attached their entire size throughout the carapace. The number of chambers can vary among taxa, though most often they have three lateral compartments, three medial chambers, and one terminal chamber. As mentioned earlier on, the act of specific abdominal muscles pulling down the viscera (or pressing back up) is exactly what allows for respiration in turtles. Specifically, it is usually the turtles large liver that pulls or pushes on the lungs. Ventral to the lungs, in the coelomic cavity, the liver of turtles is attached directly to the correct lung, and their belly is directly attached to the left lung simply by the ventral mesopneumonium, which is attached to their liver organ by the ventral mesentery. When the liver is pulled down, inspiration begins. Helping the lungs is the particular post-pulmonary septum, that is discovered in all Testudines, and it is thought to prevent the lungs from collapsing.
link to view of Yellowbellied Slider head markings
Turtles Epidermis and molting
As described above, the outer coating of the shell will be part of the skin; each scute (or plate) on the shell refers to a single revised scale. The remainder of the skin has a lot smaller scales, just like the epidermis of other reptiles. Turtles do not molt their own skins all at once as snakes do, but continuously in small items. When turtles are held in aquaria, small sheets of dead skin can be seen in the particular water (often appearing in order to be a thin item of plastic) having already been sloughed off when the animals deliberately rub on their own against an item of wood or stone. Tortoises also lose skin, but dead epidermis is allowed to accumulate into thick knobs and discs that provide protection in order to parts of the body outside the shell.
Simply by counting the rings created by the stack associated with smaller, older scutes on top of the larger, newer ones, it is possible to estimate the age group of a turtle, in case one knows the number of scutes are produced in per year. This method is not very accurate, partly due to the fact growth rate is not constant, but also since some of the scutes eventually fall away through the shell.
Turtles Braches
Terrestrial tortoises have short, durable feet. Tortoises are famous for moving slowly, simply because of their weighty, cumbersome shells, which limit stride length.
Skeleton associated with snapping turtle (Chelydra serpentina)
Amphibious turtles normally possess limbs similar to the ones from tortoises, except that the particular feet are webbed plus often have long claws. These turtles swim using all four feet within a way similar to the dog paddle, with the feet on the particular left and right side of the particular body alternately providing drive. Large turtles tend to swim less than smaller sized ones, and the really big species, such since alligator snapping turtles, hardly swim in any way, preferring in order to walk across the bottom of the river or lake. As well as webbed feet, turtles have really long claws, used in order to help them clamber on to riverbanks and floating logs upon which they bask. Male turtles tend in order to have particularly long claws, and these look like used to stimulate the woman while mating. While the majority of turtles have webbed ft, some, like the pig-nosed turtle, have true flippers, along with the digits being fused into paddles and the paws being relatively small. These species swim in the same way since sea turtles do (see below).
Sea turtles are almost entirely aquatic and have flippers instead associated with feet. Sea turtles fly with the water, using the particular up-and-down motion of the front flippers to generate drive; the back feet aren't used for propulsion but may be used as rudders with regard to steering. Compared with fresh water turtles, sea turtles possess very limited mobility upon land, and apart from the dash from the nest to the sea as hatchlings, male sea turtles normally in no way leave the sea. Women must come back on to land to lay ovum. They move very slowly and laboriously, dragging by themselves forwards using their flippers.
Conduct of Turtles
Senses of Turtles are believed to have exceptional night eyesight due to the unusually large amount of rod cells within their retinas. Turtles have color vision with the wealth of cone subtypes with sensitivities ranging through the near ultraviolet (UVA) to red. Some land turtles have very bad pursuit movement abilities, which are normally found only in predators that quest quick-moving prey, but carnivorous turtles are able in order to move their heads rapidly to snap.
Turtles Communication
The particular Arrau turtle has a sizable vocal repertoire.
While typically thought of as mute, turtles make numerous sounds when communicating. Tortoises might be vocal when dating and mating. Various types of both freshwater and sea turtles emit numerous types of calls, usually short and low regularity, from the time these are in the egg to when they are adults. These types of vocalizations may serve to create group cohesion whenever migrating.
Turtle Cleverness
See furthermore: Animal knowledge
It has been reported that wood turtles are better compared to white rats at understanding to navigate mazes. Case studies exist of turtles playing. They do, however, possess a very low encephalization quotient (relative brain to body mass), and their own hard shells enable them to live without fast reflexes or elaborate predator prevention strategies. In the laboratory, turtles (Pseudemys nelsoni) may learn novel operant jobs and have demonstrated a extensive memory of at least 7. 5 months.
Turtle Mating Techniques
An example of mounting behavior within turtles
Turtles are identified for displaying a wide variety of mating behaviors, nevertheless , they are not really known for forming pair-bonds or for being part of a social group. Once fertilization has happened and an offspring offers been produced, neither parent will provide care regarding the offspring once it's hatched. Females generally outnumber males in various turtle species (such as Green turtles), and as a result, most men will engage in multiple copulation with multiple partners throughout their lifespan. However, because of to the sexual dimorphism present in most turtle species, males must create different courting strategies or even use alternate methods in order to gain access to a potential mate. Most terrestrial varieties have males that are bigger than females, and battling between males often decides a hierarchical order in which the higher upward the order an individual is, the better the particular chance is of the individual getting access to the potential mate. For most semi-aquatic species and bottom-walking aquatic species, combat takes place less often. Males belonging to semi-aquatic and bottom-walking species instead often make use of their larger size benefit to forcibly mate using a female. In fully aquatic species, males are often smaller than females plus therefore they can not use the same strategy because their semi-aquatic relatives, which depends on overwhelming the females with power. Males in this class resort to using courtship displays in an attempt to gain mating accessibility to a female.
Combating Between Males Turtles
Saddle back Galapagos tortoise
Wood turtles are an example of the terrestrial species where the males have a hierarchical ranking system based on dominance through fighting, plus it's shown that the males with the greatest rank and thus the particular most wins in arguements have the most children.
Galapagos tortoises are an additional example of a types which has a hierarchical rank that is determined simply by dominance displays, and access to food and mates is regulated by this particular dominance hierarchy. Two male saddle backs most frequently compete for access to cactus trees, which is their source of food. The winner is the individual who stretches their neck the highest, which person gets access to the particular cactus tree, which may attract potential mates.
Push Mating Turtles
Male (left) plus female (right) radiated tortoise
The male scorpion mud turtle is an example of a bottom-walking aquatic species that relies on overwhelming females with its bigger size as a mating strategy. The male techniques the female from the rear, and often resorts to aggressive methods such as biting the female's tail or hind limbs, then the mounting behavior in which the male clasps the edges of her carapace with his forelimbs and hind limbs to hold the girl in position. The man follows this action simply by laterally waving his mind and sometimes biting the particular female's head in a good attempt to get her to withdraw her head into her shell. This exposes her cloaca, and along with it exposed, the man can attempt copulation simply by wanting to insert his holding tail.
Male radiated tortoises may also be known to make use of the force mating strategy wherein they use surrounding vegetation to trap or even prevent females from escaping, then pin them lower for copulation.
Turtles Courtship Shows
Red-eared sliders are a good example of a fully marine species where the male works a courtship behavior. Within this case the man extends his forelegs using the palms facing out plus flutters his forelegs within the female's face. Female choice is important in this method, as well as the females of some species, such as green sea turtles, aren't usually receptive. As such, they've developed certain behaviors to avoid the male's attempts in copulation, such as going swimming away, confronting the man followed by biting, or even a refusal position in which the female assumes a vertical position along with her limbs widely outspread and her plastron dealing with the male. If the particular water is too superficial to perform the refusal position, the females may resort to beaching on their own, which is a verified deterrent method, as the males will not follow them ashore.
Ecology and life history of turtles
Ocean turtle swimming
Although many turtles spend large amounts of their lives underwater, all turtles and tortoises breathe air and must surface at regular time periods to refill their lung area. They can also spend much or all of their lives on dry land. Aquatic respiration within Australian freshwater turtles will be currently being studied. Some species have large cloacal cavities that are covered with many finger-like projections. These types of projections, called papillae, have got a rich blood supply and improve the surface region of the cloaca. The turtles can take upward dissolved oxygen from the water using these papillae, in much the same way that fish use gills to respire.
Like additional reptiles, turtles lay eggs that are slightly smooth and leathery. The eggs of the largest species are usually spherical while the eggs of the rest are usually elongated. Their albumen is usually white and contains an alternative protein from bird ovum, such that it will not coagulate when cooked. Turtle eggs prepared to eat consist mainly of yolk. In some species, temperature determines whether an egg cell develops into a male or perhaps a female: a higher temperature causes a female, a lower temperature causes a male. Large numbers of ovum are deposited in openings dug into mud or even sand. They are after that covered and left to incubate by themselves. Depending on the species, the eggs will typically take 70–120 days to hatch. When the turtles hatch, they squirm their way to the surface and head toward the water. There are simply no known species in which the mom cares for her younger.
Sea turtles lay their eggs on dry, sandy beaches. Immature sea turtles are not cared regarding by the adults. Turtles can take many yrs to achieve breeding age, plus in many cases, breed of dog every few years , rather than annually.
Researchers have lately found out a turtle's internal organs usually do not steadily break lower or become less efficient over time, unlike the majority of other animals. It had been found that the liver, lungs, and kidneys associated with a centenarian turtle are usually almost indistinguishable from all those of its immature version. This has inspired hereditary researchers to start examining the turtle genome with regard to longevity genes.
A group of turtles is known as a bale.
Turtles Diet
A green sea turtle grazing on
A turtle's diet varies greatly determined by the environment by which it lives. Adult turtles typically eat marine plants; (citation needed) invertebrates like insects, snails, and worms; and have already been reported to occasionally consume dead marine animals. Several small freshwater species are carnivorous, eating small fish and many aquatic existence. However, protein is important to turtle growth and juvenile turtles are solely carnivorous.
Sea turtles usually feed on jellyfish, sponges, and other soft-bodied organisms. Some species with more robust jaws have been observed to eat shellfish, while others, including the green ocean turtle, do not consume meat at all and, instead, possess a diet largely made up of algae.
Systematics and evolution of Turtles
Main article: Turtle classification
See|Observe|Notice} also: List of Testudines households
Life restoration associated with Odontochelys semitestacea, the earliest known turtle relative along with a partial shell
"Chelonia" from Ernst Haeckel's Kunstformen der Natur, 1904
Dependent on body fossils, the first proto-turtles are believed to have existed in the late Triassic Period of the Mesozoic era, about 220 million years back, and their shell, which has remained a remarkably stable body plan, will be thought to have evolved from bony extensions of their backbones and broad ribs that expanded and grew together to form a complete shell that provided protection at every stage of its evolution, actually when the bony component of the shell was not really complete. This is supported by fossils of the freshwater Odontochelys semitestacea or even "half-shelled turtle with teeth", from the late Triassic, which have been discovered near Guangling in south west China. Odontochelys displays the complete bony plastron plus an incomplete carapace, comparable to an early phase of turtle embryonic development. Prior to this discovery, the particular earliest-known fossil turtle ancestors, like Proganochelys, were terrestrial together a complete covering, offering no clue to the evolution of this impressive anatomical feature. By the past due Jurassic, turtles had radiated widely, and their precious history becomes easier to read.
Their exact ancestry provides been disputed. It was believed they are the only surviving branch of the ancient evolutionary quality Anapsida, which includes organizations such as procolophonids, millerettids, protorothyrids, and pareiasaurs. All anapsid skulls lack a temporary opening while all some other extant amniotes have temporal openings (although in mammals, the hole has turn out to be the zygomatic arch). The particular millerettids, protorothyrids, and pareiasaurs became extinct in the particular late Permian period plus the procolophonoids during the particular Triassic.
However , it was later recommended the anapsid-like turtle head may be due to reversion rather than to anapsid descent. More recent morphological phylogenetic studies with this in mind placed turtles firmly within diapsids, slightly closer to Squamata than to Archosauria.[55][56] All molecular studies have got strongly upheld the placement of turtles within diapsids; some place turtles within Archosauria, or, more commonly, as a sister group to extant archosaurs,[58][59][60][61] though an analysis carried out by Lyson et al. (2012) recovered turtles as the sister group of lepidosaurs instead. Reanalysis of before phylogenies suggests that these people classified turtles as anapsids both simply because they assumed this particular classification (most of all of them studying what sort associated with anapsid turtles are) and because they did not sample fossil and extant taxa broadly enough with regard to constructing the cladogram. Testudines were suggested to have diverged from other diapsids between 200 and 279 million years ago, though the particular debate is far from settled. Even the traditional placement of turtles outside Diapsida cannot be dominated out at this stage. A combined analysis of morphological and molecular data conducted by Lee (2001) found turtles to end up being anapsids (though a relationship with archosaurs couldn't be statistically rejected).[64] Similarly, a morphological research conducted by Lyson ou al.. (2010) recovered all of them as anapsids most closely related to Eunotosaurus. A molecular analysis of 248 nuclear genes from sixteen vertebrate taxa suggests that turtles are a sister team to birds and crocodiles (the Archosauria).[66] The date of separation of turtles and birds and crocodiles was approximated to be 255 mil years ago. The most latest common ancestor of residing turtles, corresponding towards the split between Pleurodira and Cryptodira, was estimated to get happened around 157 million many years ago. The oldest defined crown-group turtle (member from the modern clade Testudines) will be the species Caribemys oxfordiensis from the late Jurassic period (Oxfordian stage). Through utilizing the very first genomic-scale phylogenetic analysis associated with ultraconserved elements (UCEs) to investigate the placement of turtles within reptiles, Crawford ainsi que al. (2012) also suggest that turtles are the sister group to wild birds and crocodiles (the Archosauria).
The first genome-wide phylogenetic analysis was completed simply by Wang et al. (2013). Using the draft genomes of Chelonia mydas and Pelodiscus sinensis, the team used largest turtle information set to date in their own analysis and concluded that will turtles are likely the sister group of crocodilians and birds (Archosauria). This particular placement within the diapsids suggests that the turtle lineage lost diapsid skull characteristics as it today possesses an anapsid-like skull.
The earliest known fully shelled member of the turtle lineage is the late Triassic Proganochelys. This particular genus already possessed several advanced turtle traits, and thus probably indicates numerous millions of years associated with preceding turtle evolution; this is further supported by evidence from fossil paths from the Early Triassic of the United Says (Wyoming and Utah) and from the Middle Triassic of Germany, indicating that proto-turtles already existed since early as the first Triassic. Proganochelys lacked the ability to draw its head into its shell, had a long neck, and had a long, spiked tail closing in a club. While this body form is comparable to those of ankylosaurs, it resulted from convergent development.
Turtles are divided into two extant suborders: Cryptodira and Pleurodira. The Cryptodira is the larger associated with the two groups and includes all the ocean turtles, the terrestrial tortoises, and several of the fresh water turtles. The Pleurodira are sometimes known as the particular side-necked turtles, a guide to how they retract their heads to their shells. This smaller group consists primarily of various freshwater turtles.