Taxonomy

The Diamondback Terrapin (Malaclemys terrapin) is an attractive medium sized, brackish water turtle of the family Emydidae. It is semi-aquatic in nature and ranges along the eastern and southern coasts of North America, from Cape Cod to Corpus Christi.  Diamondbacks are the only U.S. turtles that inhabit estuaries, tidal creeks and saltwater marshes where the salinity comes close to or equals that of the ocean.  It is in this type of environment that diamondbacks thrive, dining on delicacies such as crabs, snails, shrimp, fish, mussels, clams, and other assorted crustaceans.

 

Diamondback terrapins have proven to be one of the most physically variable of turtle species and even specimens within the same subspecies/populations can have vastly differing shell pattern, skin color, markings and shapes.  However, one trait that is characteristic of all diamondbacks is their grooved, concentrically patterned, diamond-shaped scutes.  It is from these intricate markings that the diamondback has derived its name.  In addition, another descriptive feature of diamondbacks, shared with their common relatives the Map turtles (Graptemys sp.), is their sexual dimorphism.  Females tend to be twice the size of males at sexual maturity.  Male diamondbacks usually attain a carapace length of 5 inches, whereas females can attain a length of 9 inches.  Females also possess larger and broader heads than males, adding to their stouter, bulkier look.  A last distinguishing trait of diamondbacks is the large size of their hind feet in proportion to their bodies.  This adaptation gives them greater mobility under the onslaught of strong tidal currents and undertows.

 

The color of diamondback carapaces can vary from black, brown, gray, orange, olive to tan; their patterns from concentric marbles, donuts, to patternless.  In addition, their carapaces can be either deeply or slightly grooved, sporting either huge vertebral keels or slight knobs.  Diamondback skin color and pattern are equally diverse with colors ranging from gray, white, olive, slate blue to even black; and patterns range from small dots, big spots, lines, bold stripes, combination of spots and lines, and patternless.  To further complicate things, the intergrading of populations when commercial harvesting was at its peak further confounded taxonomical identification at the sub-specific level.  Terrapin meat was once greatly esteemed as a delicacy from the late 1800s' into the Roaring Twenties; hence the reason for commercial harvesting (the word "terrapin" was actually derived from a french word meaning turtle soup).  When the demand for terrapin meat finally waned due to the stock market crash and Prohibition (terrapin meat was usually cooked with wine), large shipments of diamondbacks from various parts of their range were reported to have been released into the wild.  The introduction of these shipments compromised the purity of native populations and hence complicated the identification of the east coast subspecies.
 

There are currently seven recognized diamondback subspecies: the Northern Diamondback Terrapin (M.t. terrapin), the Carolina Diamondback Terrapin (M.t. centrata), the Florida East Coast Diamondback Terrapin (M.t. tequesta), the Mangrove Diamondback Terrapin (M.t. rhizophorarum), the Ornate Diamondback Terrapin (M.t. macrospilota), the Mississippi Diamondback Terrapin (M.t. pileata) and the Texas Diamondback Terrapin (M.t. littoralis). These subspecific delineations were mainly based on phenotypic differences. With this in mind, some have proposed splitting the Mangrove Diamondback Terrapin into Upper Keys and Lower Keys subspecies due to their differing phenotypes. To further complicate things, diamondback terrapins have also been found in Bermuda. They appear to be native, appear identical to the Carolina Diamondback Terrapin and have yet to be categorized.

Recently, genetic studies have further narrowed the species down to four regional genetic clusters: Northeast Atlantic (MA), Coastal Mid-Atlantic (NY to SC), FL and TX/LA. However, further sampling must occur to substantiate these findings so for now, we will continue our taxonomic discussion based on the accepted seven subspecies.

Diamondback Terrapin (Malaclemys terrapin) subspecies (A-G dotted area, see Ernst et al. 1994) designations and new genetic groupings (1-4). A "*" indicates locations with no samples.

Northern Diamondback Terrapin

Latin Name: Malaclemys terrapin terrapin

Range: Cape Cod to Cape Hatteras

Carapace: lightly sculpted, black to light brown with slight dorsal keel and concentric markings.
Skin: light specks and/or streaks with brighter individuals possessing bold spots and dashes.  Color varies from dark gray to white.
Distinguishing feature: the main subspecies available in herpetoculture. Concentric phenotypes with teardrop markings and bold concentric circles on the carapace are highly sought after yet readily available.

Carolina Diamondback Terrapin

Latin Name: Malaclemys terrapin centrata

Range: Cape Hatteras to Flagler County, FL

Carapace: lightly sculpted, black to light brown with slight dorsal keel and concentric markings.
Skin: light specks and/or streaks with brighter individuals possessing bold spots and dashes.  Color varies from dark gray to white.
Distinguishing feature: The Carolina Diamondback Terrapin is virtually indistinguishable from its northern counterpart due to the mixing of populations that occurred in the early 1900s. Bermuda populations of diamondback terrapins also share identical morphological features to this subspecies. Concentric phenotypes with teardrop markings and bold concentric circles also occur naturally but this subspecies is virtually non-existent in herpetoculture due to statewide regulations across its boundaries.

Florida East Coast Diamondback Terrapin

Latin Name: Malaclemys terrapin tequesta

Range: Flagler County to the Upper Keys

Carapace: deeply sculpted, black to gray with sometimes lighter scute centers with slight dorsal keel.  Concentric rings are generally absent.
Skin: variable, with specks, large spots and even patternless.  Color is usually gray or white.  Mustache is normally present.
Distinguishing feature: lack of concentric carapace markings. This subspecies is unfortunately very rare due to commercial encroachment on its native habitat and predation by raccoons.

Mangrove Diamondback Terrapin

Latin Name: Malaclemys terrapin rhizophorarum

Range: Florida Keys

Carapace: smooth, black to light brown with slight dorsal keel and concentric markings.
Skin: spotted or streaked against a background of gray.  The Upper Keys populations sport bold spots and dashes.
Distinguishing feature: Very rarely seen subspecies prone to illegal commercial harvesting for the east Asian pet trade but seldom offered in the U.S. Continued harvesting is unsustainable and dangerously threatening to the subspecies.

Ornate Diamondback Terrapin

Latin Name: Malaclemys terrapin macrospilota

Range: West Coast of Florida

Carapace: deeply sculpted, black to dark gray with high dorsal keel.  Scute centers are typically orange or yellow.  Concentric markings are almost completely absent.  Marginals can be checkered or completely orange/yellow.
Skin: thin, making their heads appear pink at times.  Light speckling is usually present although patternless individuals are also known to occur.  Color is generally a shade of gray although lavender does occur with some frequency and white rarely.
Distinguishing feature: arguably the most attractive and easily distinguishable subspecies.  The contrast of orange/yellow scute centers against an otherwise dark carapace is very pleasing indeed.

Mississippi Diamondback Terrapin

Latin Name: Malaclemys terrapin pileata

Range: Panhandle of Florida to western Louisiana

Carapace: deeply grooved, black to dark gray or sometimes golden with high dorsal keel. Concentric markings are usually absent against the darker individuals but present in lighter individuals.
Skin: mostly light speckling or large spots against a black or gray background. Mustache often present with the exception of western Louisiana populations which are highly variable with sometimes greenish and bluish skin and blonde crowns.
Distinguishing feature: populations in Mississippi tend towards melanism. However, the lighter (hypomelanistic) western Louisiana populations are known for their attractiveness due to intergrading with other subspecies during the heyday of terrapin food farming. Most if not all Texas Diamondback Terrapins in the hobby are actually Mississippi Diamondback Terrapins from Louisiana.

Texas Diamondback Terrapin

Latin Name: Malaclemys terrapin littoralis

Range: Texas coast down to Corpus Christi

Carapace: deeply grooved, black to brown high dorsal keel.  Scute centers are sometimes lighter and concentric markings are generally invisible due to the background color.
Skin: lightly speckled, dark gray with sometimes greenish heads.
Distinguishing feature: The Texas Diamondback Terrapin is protected statewide and possession is prohibited. Most, if not all specimens in captivity are actually Mississippi Diamondback Terrapins from western Louisiana which are more variable and attractive than their Texas cousins. 

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