The diamondback terrapin (Malaclemys terrapin) or simply terrapin, is a species of turtle native to the brackish coastal tidal marshes of the eastern and southern United States, and in Bermuda.^[5] It belongs to the monotypic genus, Malaclemys. It has one of the largest ranges of all turtles in North America, stretching as far south as Florida Keys and as far north as Cape Cod.^[6]

The name “terrapin” is derived from the Algonquian word torope.^[7] It applies to Malaclemys terrapin in both British English and American English. The name originally was used by early European settlers in North America to describe these brackish-water turtles that inhabited neither freshwater habitats nor the sea. It retains this primary meaning in American English.^[7] In British English, however, other semi-aquatic turtle species, such as the red-eared slider, might be called a terrapin.

The common name refers to the diamond pattern on top of its shell (carapace), but the overall pattern and coloration vary greatly. The shell is usually wider at the back than in the front, and from above its appears wedge-shaped. The shell coloring can vary from brown to grey, and its body color can be grey, brown, yellow, or white. All have a unique pattern of wiggly, black markings or spots on their body and head. The diamondback terrapin has large webbed feet.^[8] The species is sexually dimorphic in that the males grow to approximately 13 cm (5.1 in), while the females grow to an average of around 19 cm (7.5 in), though they are capable of growing larger. The largest female on record was just over 23 cm (9.1 in) in length. Specimens from regions that are consistently warmer in temperature tend to be larger than those from cooler, more northern areas.^[9]Male diamondback terrapins weigh 300 g (11 oz) on average, while females weigh around 500 g (18 oz).^[10] The largest females can weigh up to 1,000 g (35 oz)

(photos taken at Camden Aquarium)