link to view of Yellowbellied Slider head markings

link to view of Yellowbellied Slider head markings

Turtles are diapsids of the order Testudines (or Chelonii) characterized by a special bony or cartilaginous shell created from their ribs plus acting as a protect. "Turtle" may refer in order to the order as a whole (American English) or even 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 mil years ago, making turtles one of the oldest reptile groups and a more ancient group compared to snakes or crocodilians. Of the 356 known varieties alive today, some are highly endangered.

Turtles are usually ectotherms—animals commonly called cold-blooded—meaning that their internal heat varies according to the particular ambient environment. However, because of their high metabolic rate, leatherback sea turtles have a body heat that is noticeably higher than that of the surrounding water. Turtles are classified as amniotes, along with other reptiles, parrots, and mammals. Like additional amniotes, turtles breathe atmosphere and do not place eggs underwater, although numerous species live in or even around water. The study of turtles is called cheloniology, after the Greek phrase for turtle. It is usually also sometimes called testudinology, after the Latin title for turtles.

Differences can be found in usage of the common terms turtle, tortoise, and terrapin, based on the range of English being utilized. These terms are typical names and do not reflect precise biological or taxonomic distinctions.

Turtle may either refer to the order because a whole, or to particular turtles that make up a form taxon which is not monophyletic, or may be limited to only aquatic species. Tortoise usually relates to any land-dwelling, non-swimming chelonian. Terrapin is used to describe several species associated with small, edible, hard-shell turtles, typically those found in brackish waters.

In Northern America, all chelonians are commonly called turtles. Tortoise is used only within reference to fully terrestrial turtles or, more narrowly, just those members of Testudinidae, the family of modern property tortoises. Terrapin may relate to small semi-aquatic turtles that live in fresh and brackish water, specifically the diamondback terrapin (Malaclemys terrapin). Although the people from the genus Terrapene dwell mostly on land, they are referred to as box turtles rather than tortoises. The particular American Society of Ichthyologists and Herpetologists uses "turtle" to describe all species of the order Testudines, regardless of whether they are land-dwelling or sea-dwelling, and uses "tortoise" being a more specific expression for slow-moving terrestrial species.

In the United Kingdom, the word turtle is used for water-dwelling species, including ones known in the US as terrapins, however, not for terrestrial species, that are known only as tortoises.

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The word chelonian will be popular among veterinarians, scientists, plus conservationists working with these animals being a catch-all name for any member of the superorder Chelonia, including just about all turtles living and vanished, as well as their immediate ancestors. Chelonia is usually based on the Ancient greek word for turtles, χελώνη chelone; Greek χέλυς chelys "tortoise" is also utilized 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 distinction, as all of these are referred to by the particular same name. For instance , within Spanish, the word tortuga is used for turtles, tortoises, and terrapins. The sea-dwelling turtle is tortuga marina, a freshwater species tortuga de río, plus a tortoise tortuga terrestre.

The largest living chelonian is the leatherback sea turtle (Dermochelys coriacea), which usually reaches a shell length of 200 cm (6. six ft) and can achieve a weight of more than 900 kg (2, 000 lb). Freshwater turtles are usually generally smaller, but with the largest species, the particular Asian softshell turtle Pelochelys cantorii, a few individuals have been reported upward to 200 cm (6. 6 ft). This dwarfs even the better-known alligator snapping turtle, the biggest chelonian in North The united states, which attains a shell length of up in order to 80 cm (2. six ft) and weighs since much as 113. four kg (250 lb).

Large tortoises of the overal Geochelone, Meiolania, and other people were relatively widely dispersed around the world into prehistoric periods, and therefore are known to have existed in North and South America, Australia, plus Africa. They became wiped out at the same time as the appearance of man, and it is assumed humans hunted them for food. The only surviving giant tortoises are usually on the Seychelles and Galápagos Islands and can grow to over 130 cm (51 in) in length, and weigh about three hundred kg (660 lb).

The largest ever chelonian has been Archelon ischyros, a Late Cretaceous sea turtle recognized to have been up to 4. 6 m (15 ft) long.

Turtles that live on land Pets4Homes

The tiniest turtle is the speckled padloper tortoise of Southern Africa. It measures no more than 8 cm (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 will ranges from Canada to South America. The covering duration of many species within this group is much less than 13 cm (5. 1 in) in length.

Turtles are divided into two groups, according to how 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 to the side, anterior to glenohumeral joint girdles, while the suborder Cryptodira retracts straight back again, between shoulder girdles. These types of motions are largely due to the morphology plus arrangement of cervical backbone. Of all recent turtles, the cervical column is made up of nine joints plus eight vertebrae, which are usually individually independent. Since these types of vertebrae are not joined and are rounded, the neck is more flexible, being able to bend in the backwards and sideways directions. The major function and evolutionary inference of neck retraction is usually thought to be for feeding rather than protection. Neck retraction and reciprocal extension allows the turtle to achieve out further in order to capture prey while swimming. Neck expansion creates suction when 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 protection the shell offers the head when this is retracted is as a result not the main function of retraction, thus is usually an exaptation. As for the difference between the particular two methods of retraction, both Pleurodirans and Cryptodirans use the quick extension of the neck as a method of predation, so the difference in retraction mechanism is just not due to a difference in ecological niche.

Head

Most turtles that spend most associated with their lives on property have their eyes looking straight down at objects in front of them. Some marine turtles, such as snapping turtles and soft-shelled turtles, have eyes closer in order to the top of the mind. These types of turtle can hide from predators in shallow water, where these people lie entirely submerged other than for their eyes and nostrils. Near their eyes, sea turtles possess intrigue that produce salty holes that rid their body of excess salt taken in through the water they drink.

Turtles have rigid beaks and use their teeth to cut and munch food. Instead of having teeth, which they appear in order to have lost about 150-200 million years ago, the particular upper and lower jaws of the turtle are covered by horny ridges. Carnivorous turtles usually have knife-sharp ridges for cutting through their prey. Herbivorous turtles have serrated-edged side rails that help them reduce through tough plants. These people use their tongues to swallow food, but as opposed to most reptiles, they can not stick out their tongues in order to catch food.

ShellPrimary article: Turtle shellTop of the shell of the turtle is known as the carapace. The particular lower shell that encases the belly is called the plastron. The carapace and plastron are joined up with together on the turtle's sides by bony buildings called bridges. The inner layer of a turtle's shell is made upward of about 60 bones that include portions associated with the backbone and the ribs, meaning the turtle cannot crawl away from its shell. In most turtles, the outer layer from the shell is covered simply by horny scales called scutes which are part of its outer skin, or skin. Scutes are made up of the fibrous protein keratin that will also makes up the scales of other reptiles. These scutes overlap the particular seams between the shell bones and add power to the shell. Some turtles do not possess horny scutes; for example, the leatherback ocean turtle as well as the soft-shelled turtles have shells covered with leathery skin instead.

The shape of the covering gives helpful clues about how exactly a turtle lives. Many tortoises have a huge, dome-shaped shell that can make it difficult for potential predators to crush the cover between their jaws. One of the few exclusions is the African hot cake tortoise, which has a flat, flexible shell that allows it to conceal in rock crevices. Most aquatic turtles have smooth, streamlined shells, which help within swimming and diving. American snapping turtles and musk turtles have small, cross-shaped plastrons that give them more efficient leg motion for walking along the particular bottom of ponds and streams. Another exception will be the Belawan Turtle (Cirebon, West Java), which has sunken-back soft-shell.

The color of a turtle's shell may vary. Shells are commonly coloured brown, black, or olive green. In some species, covers may have red, fruit, yellow, or grey markings, often spots, lines, or even irregular blotches. Probably the most vibrant turtles is the eastern painted turtle, which consists of a yellow plastron and a black or olive shell with red markings around the rim.

Tortoises, being land-based, have instead heavy shells. In contrast, aquatic and soft-shelled turtles have lighter shells that help them avoid sinking in water and swim faster with more agility. These lighter shells possess large spaces called fontanelles between the shell bone fragments. The shells of leatherback sea turtles are really lighting because they lack scutes and contain many fontanelles.

It has been recommended by Jackson (2002) that will the turtle shell may function as pH buffer. To endure through anoxic conditions, such as winter season periods trapped beneath glaciers or within anoxic dirt at the bottom of ponds, turtles utilize two general physiological mechanisms. In the case of prolonged periods associated with anoxia, it has been shown that this turtle cover both releases carbonate buffers and uptakes lactic acid.

Sea Turtle Species Sea Turtle Exploration

Respiration Turtles

Respiration, for many amniotes, is achieved by the particular contraction and relaxation of specific muscles (i. e. intercostals, abs, and/or the diaphragm) mounted on an inner rib-cage that can increase or contract the entire body wall thus assisting airflow out and in of the lung area. The ribs of Chelonians, however, are fused with their carapace and external to their pelvic plus pectoral girdles, a function unique among turtles. This rigid shell is not really capable of expansion, plus by rendering their rib-cage immobile, Testudines have experienced to evolve special adaptations for respiration.

Turtle pulmonary ventilation occurs by using specific groups of abdominal muscles attached to their viscera and shell that draw the lungs ventrally throughout inspiration, where air is drawn in via a negative pressure gradient (Boyle's Law). In expiration, the contraction of the transversus abdominis is the driving push by propelling the viscera into the lungs plus expelling air under optimistic pressure. Conversely, the calming and flattening of the oblique abdominis muscle draws 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 used in conjunction with the transverse abdominis during motivation, as well as the serratus, which movements with all the abdominal oblique associated expiration.

The lungs of Testudines are multi-chambered and attached their entire size down the carapace. The amount of chambers can differ between taxa, though most commonly they will have three lateral chambers, three medial chambers, and one terminal chamber. As previously mentioned, the act of specific abdominal muscles pulling down the viscera (or pressing back up) is what allows for respiration within turtles. Specifically, it is the turtles large liver that pulls or pushes on the lungs. Ventral to the lungs, in the coelomic cavity, the liver of turtles is connected directly to the correct lung, and their abdomen is directly attached to the left lung by the ventral mesopneumonium, which is attached to their liver organ with the ventral mesentery. When the liver is taken down, inspiration begins. Assisting the lungs is the particular post-pulmonary septum, which is discovered in all Testudines, and is thought to prevent the lungs from collapsing.

Encyclopaedia of Babies of Beautiful Wild Animals: The Baby Turtle

Turtles Pores and skin and molting

As mentioned above, the outer coating of the shell is part of the pores and skin; each scute (or plate) on the shell refers to a single revised scale. The remainder of the skin has much smaller scales, similar to the pores and skin of other reptiles. Turtles do not molt their own skins all at as soon as as snakes do, but continuously in small items. When turtles are kept in aquaria, small linens of dead skin may be seen in the particular water (often appearing in order to be a thin piece of plastic) having already been sloughed off when the animals deliberately rub by themselves against some wood or even stone. Tortoises also shed skin, but dead epidermis is permitted to accumulate directly into thick knobs and plates that provide protection in order to parts of the body outside the shell.

Simply by counting the rings formed by the stack of smaller, older scutes on top of the larger, newer types, you are able to estimate the age of a turtle, when one knows the number of scutes are produced in per year. This method is not really very accurate, partly due to the fact growth rate is not constant, but also since some of the scutes eventually fall away from the shell.

Turtles Braches

Terrestrial tortoises have short, durable feet. Tortoises are well-known for moving slowly, simply because of their large, cumbersome shells, which limit stride length.

Skeleton of snapping turtle (Chelydra serpentina)

Amphibious turtles normally possess limbs similar to the ones from tortoises, except that the particular feet are webbed and often have long paws. These turtles swim making use of all four feet within a way similar in order to the dog paddle, with the feet on the particular left and right side of the particular body alternately providing drive. Large turtles tend in order to swim less than smaller sized ones, and the extremely big species, such as alligator snapping turtles, barely swim at all, preferring to walk along the bottom of the river or river. As well as webbed feet, turtles have extremely long claws, used to help them clamber on to riverbanks and floating logs upon which they bask. Male turtles tend to have particularly long claws, and these appear to be used to stimulate the female while mating. While many turtles have webbed feet, some, such as the pig-nosed turtle, have true flippers, with the digits being joined into paddles as well as the claws being relatively small. These types of species swim in the same way since sea turtles do (see below).

Sea turtles are usually almost entirely aquatic plus have flippers instead of feet. Sea turtles fly through the water, using the particular up-and-down motion of the particular front flippers to create thrust; the back feet are not used for propulsion yet can be used as rudders regarding steering. Compared with fresh water turtles, sea turtles have got very limited mobility on land, and in addition to the dash from the nest to the sea as hatchlings, man sea turtles normally never leave the sea. Females must come back on to land to lay ovum. They move very slowly and laboriously, dragging themselves forwards with their flippers.

Behavior of Turtles

Senses of Turtles are thought to have exceptional night vision due to the unusually large amount of rod cells within their retinas. Turtles have color vision with a 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 just in predators that hunt quick-moving prey, but carnivorous turtles are able in order to move their heads quickly to snap.

Turtles Communication

The particular Arrau turtle has a sizable vocal repertoire.

While typically thought of as mute, turtles make different sounds when communicating. Tortoises might be vocal when courting and mating. Various varieties of both freshwater and sea turtles emit many types of calls, often short and low regularity, from the time these are in the egg to if they are adults. These types of vocalizations may serve in order to create group cohesion when migrating.

Turtle Cleverness

See furthermore: Animal cognition

It provides been reported that wood turtles are better compared to white rats at studying to navigate mazes. Situation studies exist of turtles playing. They do, however, have got a very low encephalization quotient (relative brain in order to body mass), and their hard shells enable them to live without fast reflexes or elaborate predator avoidance strategies. In the laboratory, turtles (Pseudemys nelsoni) can learn novel operant duties and have demonstrated a long-term memory of at minimum 7. 5 months.

Turtle Mating Methods

An example of mounting behavior in turtles

Turtles are known 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 team. Once fertilization has happened and an offspring provides been produced, neither mother or father will provide care for the offspring once it's hatched. Females generally outnumber males in various turtle species (such as Eco-friendly turtles), and as a result, most males will participate in multiple copulation with multiple partners all through their lifespan. However, because of to the sexual dimorphism present in most turtle species, males must develop different courting strategies or use alternate methods to gain access to a potential mate. Most terrestrial types have males that are usually larger than females, and battling between males often determines a hierarchical order within which the higher upward the order an person 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 happens less often. Males that belong to semi-aquatic and bottom-walking species instead often use their larger size benefit to forcibly mate with a female. In fully marine species, males are often smaller than females and therefore they can not use the same strategy as their semi-aquatic relatives, which relies on overpowering the females with strength. Males in this category resort to using courtship displays in an try to gain mating accessibility to a female.

Fighting Between Males Turtles

Saddle back Galapagos tortoise

Wood turtles invariably is 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 highest rank and thus the most wins in fights have the most offspring.

Galapagos tortoises are another example of a species which has a hierarchical rank that is determined simply by dominance displays, and entry to food and partners is regulated by this dominance hierarchy. Two male saddle backs most usually compete for access in order to cactus trees, which is their particular source of food. The winner is the person who stretches their neck of the guitar the highest, which person gets access to the cactus tree, which can attract potential mates.

Push Mating Turtles

Male (left) plus female (right) radiated tortoise

The male scorpion dirt turtle is an example of a bottom-walking marine species that depends on overpowering females with its bigger size as a mating strategy. The male methods the feminine from the back, and often resorts in order to aggressive methods like biting the female's tail or hind limbs, then a 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 by laterally waving his mind and sometimes biting the particular female's head in an attempt to get the girl to withdraw her head into her shell. This reveals her cloaca, and along with it exposed, the male can attempt copulation by wanting to insert his grasping tail.

Male radiated tortoises will also be known to use the force mating technique wherein they use around vegetation to trap or prevent females from getting away, then pin them lower for copulation.

Turtles Courtship Shows

Red-eared sliders are an sort of a fully aquatic species where the male works a courtship behavior. In this case the man extends his forelegs with the palms facing out and flutters his forelegs within the female's face. Female options are important in this method, and the females of some species, such as green sea turtles, aren't usually receptive. Therefore, they've developed certain behaviors to avoid the male's attempts at copulation, such as going swimming away, confronting the male followed by biting, or a refusal position in which the female assumes a vertical position along with her limbs widely outspread and her plastron facing the male. If the water is too shallow to perform the refusal position, the females will certainly resort to beaching on their own, which is a verified deterrent method, as the males is not going to follow them ashore.

Ecology and life history of turtles

Ocean turtle swimming

Although several turtles spend large quantities of their lives underwater, all turtles and tortoises breathe air and must surface at regular intervals to refill their lungs. They can also invest much or all of their lives on dry land. Aquatic respiration within Australian freshwater turtles will be currently being studied. Several species have large cloacal cavities that are lined with many finger-like projections. These types of projections, called papillae, have a rich blood provide and raise the surface region of the cloaca. The particular turtles can take upward dissolved oxygen from the water using these papillae, in much the same method that fish use gills to respire.

Like other reptiles, turtles lay ovum that are slightly gentle and leathery. The eggs of the largest species are usually spherical while the eggs of the rest are elongated. Their albumen will be white and contains a different protein from bird ovum, such that it will not coagulate when cooked. Turtle eggs ready to eat consist mainly of yolk. In some species, heat determines whether an egg develops into a male or a female: a increased temperature the female, the lower temperature causes a man. Large numbers of ovum are deposited in holes dug into mud or sand. They are then covered and left to incubate by themselves. Depending upon the species, the ovum will typically take 70–120 days to hatch. Once the turtles hatch, they squirm their way to the particular surface and head toward the water. You can find no known species where the mother cares for her youthful.

Sea turtles lay their own eggs on dry, sandy beaches. Immature sea turtles are not cared regarding by the adults. Turtles can take many years to achieve breeding age, and in many cases, breed of dog every few years instead of annually.

Researchers have recently found out a turtle's organs tend not to slowly but surely break straight down or become less efficient over time, unlike the majority of other animals. It had been found that the liver, lungs, and kidneys of a centenarian turtle are usually almost indistinguishable from all those of its immature version. This has inspired genetic researchers to commence evaluating 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 differs greatly based on the environment by which it lives. Mature turtles typically eat marine plants; (citation needed) invertebrates for example insects, snails, plus worms; and have already been reported to occasionally consume dead marine animals. Many small freshwater species are usually carnivorous, eating small seafood and an array of aquatic existence. However, protein is important to turtle growth and juvenile turtles are solely carnivorous.

Sea turtles typically feed on jellyfish, sponges, and other soft-bodied organisms. Some species with more powerful jaws have been observed to eat shellfish, whilst others, including the green sea turtle, do not eat meat at all plus, instead, possess a diet mostly made up of algae.

Systematics and evolution of Turtles

Main article: Turtle classification

See|Observe|Notice} also: List of Testudines households

Life restoration of Odontochelys semitestacea, the oldest known turtle relative with a partial shell

"Chelonia" from Ernst Haeckel's Kunstformen der Natur, 1904

Based on body fossils, the first proto-turtles are believed to have existed in the late Triassic Period of the Mesozoic era, regarding 220 million years ago, and their shell, which has remained a incredibly stable body plan, will be thought to have evolved from bony extensions of their particular backbones and broad steak that expanded and grew together to form a complete shell that offered protection at every phase 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 a complete bony plastron and an incomplete carapace, comparable to an early stage of turtle embryonic advancement. Prior to this discovery, the particular earliest-known fossil turtle forefathers, like Proganochelys, were terrestrial and had a complete covering, offering no clue to the evolution of the impressive anatomical feature. With the past due Jurassic, turtles had extended widely, and their fossil history becomes much easier to read.

Their actual ancestry offers been disputed. It has been believed they are the only surviving branch associated with the ancient evolutionary quality Anapsida, which includes organizations for example procolophonids, millerettids, protorothyrids, and pareiasaurs. All anapsid skulls lack a temporal opening while all other extant amniotes have temporary openings (although in mammals, the hole has become the zygomatic arch). The millerettids, protorothyrids, and pareiasaurs became extinct in the late Permian period plus the procolophonoids during the Triassic.

However , it was later recommended that this anapsid-like turtle skull 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 possess strongly upheld the placement of turtles within diapsids; some place turtles within Archosauria, or, more generally, as a sister team to extant archosaurs,[58][59][60][61] though an analysis performed by Lyson et ing. (2012) recovered turtles since the sister group of lepidosaurs instead. Reanalysis of prior phylogenies suggests that they will classified turtles as anapsids both simply because they assumed this particular classification (most of all of them studying what sort of anapsid turtles are) plus because they did not really sample fossil and extant taxa broadly enough regarding constructing the cladogram. Testudines were suggested to have diverged from other diapsids between 200 and 279 mil years ago, though the particular debate is far from settled. Even the traditional placement of turtles outdoors Diapsida cannot be dominated out at this point. A combined analysis associated with morphological and molecular data conducted by Lee (2001) found turtles to be anapsids (though a relationship with archosaurs couldn't end up being statistically rejected).[64] Similarly, a morphological research conducted by Lyson ainsi que al.. (2010) recovered them as anapsids most carefully 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 wild birds and crocodiles was approximated to be 255 million in years past. The most recent common ancestor of living turtles, corresponding towards the split between Pleurodira and Cryptodira, was estimated to get happened around 157 million yrs ago. The oldest definitive crown-group turtle (member of the modern clade Testudines) is the species Caribemys oxfordiensis from the late Jurassic period (Oxfordian stage). Through utilizing the first genomic-scale phylogenetic analysis associated with ultraconserved elements (UCEs) to check into the placement of turtles within reptiles, Crawford et al. (2012) also recommend that turtles are a sister group to birds and crocodiles (the Archosauria).

The first genome-wide phylogenetic analysis was completed by Wang et al. (2013). Using the draft genomes of Chelonia mydas plus Pelodiscus sinensis, the group used the largest turtle information set to date in their own analysis and concluded that will turtles are likely a sister group of crocodilians and birds (Archosauria). This particular placement within the diapsids suggests that the turtle lineage lost diapsid head characteristics as it now possesses an anapsid-like head.

The earliest known completely shelled member of the particular turtle lineage is the late Triassic Proganochelys. This genus already possessed numerous 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 will proto-turtles already existed since early as the Early Triassic. Proganochelys lacked the opportunity to pull its head into its shell, had a long neck, and had a long, spiked tail finishing in a club. While this body form is comparable to those of ankylosaurs, it resulted from convergent advancement.

Turtles are divided in to 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 side-necked turtles, a guide to the way they retract their heads to their shells. This smaller group consists primarily of various freshwater turtles.