Tortoises are a family, Testudinidae, of land-dwelling reptiles in the order Testudines. Tortoises are shielded from predators by a shell. The top part of the shell is the carapace, the underside is the plastron, and the two are connected by the bridge. The carapace is fused to both the vertebrae and ribcage, and tortoises are unique among vertebrates in that the pectoral and pelvic girdles are inside, rather than outside, the ribcage. Tortoises can vary in size from a few centimeters to two meters. They are usually diurnal animals with tendencies to be crepuscular depending on the ambient temperatures. They are generally reclusive animals.
Turtles are reptiles of the order Testudines (or Chelonii) characterised by a special bony or cartilaginous shell developed from their ribs and acting as a shield. "Turtle" may refer to the order as a whole (American English) or to fresh-water and sea-dwelling testudines (British English).
Differences exist in usage of the common terms turtle, tortoise, and terrapin, depending on the variety of English being used; usage is inconsistent and contradictory. These terms are common names and do not reflect precise biological or taxonomic distinctions.
The 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" as a more specific term for slow-moving terrestrial species. General American usage agrees; turtle is often a general term (although some restrict it to aquatic turtles); tortoise is used only in reference to terrestrial turtles or, more narrowly, only those members of Testudinidae, the family of modern land tortoises; and terrapin may refer to turtles that are small and live in fresh and brackish water, in particular the diamondback terrapin (Malaclemys terrapin). In America, for example, the members of the genus Terrapene dwell on land, yet are referred to as box turtles rather than tortoises.
Illustration depicting organisms classified as Chelonia (turtles)
Illustration depicting organisms classified as Chelonia (turtles). The 89th plate from Ernst Haeckel's "Kunstformen der Natur" (Art forms of Nature) (1904),
Haeckel Chelonia Haeckel Chelonia big spots
1: Leatherback Turtle -- Dermatochelys coriacea (Blainville) = Dermochelys coriacea (Vandelli, 1761)
2: Hawksbill Turtle -- Caretta imbricata (Gray) = Eretmochelys imbricata (Linnaeus, 1766)
3: Argentine Snake-necked Turtle -- Hydromeda tectifera (Wagler) = Hydromedusa tectifera Cope, 1869
4: Mata mata -- Chelys fimbriata (Duméril) = Geochelone nigra (Quoy & Gaimard, 1824)
5: Geometric Tortoise -- Testudo geometrica (Linné) = Psammobates geometricus (Linnaeus, 1758)
6: Galápagos Tortoise -- Testudo elephantina (Duméril) = Dipsochelys dussumieri Gray, 1831
7: Common Snapping Turtle -- Chelydra serpentina (Schweigger) = Chelydra serpentina (Linnaeus, 1758)
Tortoises in art
Left: 'Jurōjin, Deer and Tortoises in a Landscape' by Shibata Zeshin, 1889, ink and color on silk, Honolulu Museum of Art.
Right: 'Tortoise on a River Bank' by Shibata Zeshin, c. 1873-91, ink on paper, Honolulu Museum of Art.
Angonoka tortoise (Astrochelys yniphora)
The angonoka tortoise (Astrochelys yniphora) is a critically endangered species of tortoise endemic to Madagascar. It is also known as the angonoka, ploughshare tortoise, Madagascar tortoise, or Madagascar angulated tortoise (Wikipedia).
This species is one of the rarest land tortoises in the world. Its common name refers to the appearance of the 'gular scute' at the lower part of the shell (plastron), which is drawn out into a plough-shaped projection between the front legs. The upper shell (carapace) is hard, highly domed and brown in colour, with prominent concentric growth rings on each scute. Males are larger than females. (eol.org)
Angulate tortoise (Chersina angulata)
The angulate tortoise (Chersina angulata) is a species of tortoise found in dry areas and coastal scrub vegetation in South Africa. This species is highly distinctive and is now classified by itself, in the monotypic Chersina genus.
Identification: A small, shy tortoise with a relatively variable shell, they can often be distinguished by their prominent "bowsprits", which are protrusions of the "gular" shields, from their plastrons under their chins. These are used by males to fight for territory or females. Uniquely, this species has only one gular shield under its chin; all other southern African tortoises have a divided/double scaled gular. Angulate specimens have 5 claws on their front legs and 4 on each back leg. They also, like most other southern African tortoises, have a nuchal scute. (Wikipedia).
Left: Two male Chersina angulata tortoises a male Chersina angulata tortoise demonstrating courting behaviour to another male. Cape Town. South Africa.
Right: Female Chersina angulata tortoise in Cape Town.
Radiated tortoise (Astrochelys radiata)
The radiated tortoise (Astrochelys radiata) is a species in the family Testudinidae. Although this species is native to and most abundant in southern Madagascar, it can also be found in the rest of this island, and has been introduced to the islands of Réunion and Mauritius. It is a very long-lived species, with recorded lifespans of at least 188 years. These tortoises are classified as Critically Endangered by the IUCN, mainly because of the destruction of their habitat and because of poaching. (Wikipedia).
Geometric tortoise (Psammobates geometricus)
The geometric tortoise is a critically endangered species of tortoise and one of three members of the genus, Psammobates. It is found in a very small section in the South-Western Cape of South Africa.
It has a very strong, black and yellow patterned carapace, used for defense against predators. The patterns are arranged in ray-like markings and help the tortoise blend in with its environment. From a birds eye view the shell has geometrical symbols on it thus giving it its name. This tortoise is very small, and a full grown tortoise can only reach about 5 to 6 inches in diameter. (Wikipedia).
Image source: The Tortoise Farm Nature Reserve (wildlifeforall.org)
Left: Psammobates geometricus Psammobates geometricus has lost 97 per cent of its habitat.
Right: Psammobates geometricus (Illustration) In "Tortoises, terrapins, and turtles" : drawn from life / by James de Carle Sowerby and Edward Lear.
Left: Psammobates geometricus (Illustration) Crop detail of the 89th plate from Ernst Haeckel's "Kunstformen der Natur" (Art forms of Nature) (1904)
Right: Psammobates geometricus (Illustration) Detail of the 89th plate from Ernst Haeckel's "Kunstformen der Natur" (Art forms of Nature) (1904)