Some people have mistaken turtles and clams to be related because they share a few similar traits, such as having a shell. However, just because they have this in common does not make them related. Turtles and clams are two completely different creatures. Peanuts have shells too, but that doesn’t make them anymore related to a turtle than you or I.
Turtles are classified as being reptiles of the order Testudines (the crown group of the super order Chelonia) characterized by a special bony orcaartilaginous shell that is developed from their ribs and acts as a type of shield.
The order Testudines includes both extant (still living) and extinct (species that are no longer living) species. The earliest known turtles date back some 200 million years ago, which makes them one of the oldest reptile groups and a more ancient group than lizards, snakes and even crocodiles.
Turtles, different from some reptiles are ectotherms (cold blooded) which means that their internal temperature varies according to their ambient environment. Some species of turtles have been known to have noticeably higher body temperatures than the water they are surrounded by due to their high metabolic rates. Turtles are amniotes (includes reptiles, dinosaurs, birds, and mammals). This means that they breathe air and do not lay eggs underwater. However, many species are known to live in or around water.
Now as far as clams go, the word “clam” can actually be applied to freshwater mussels as well as other freshwater bivalves and some marine bivalves. In the United States the general term covers all bivalve mollusks but can also be used in a more limited sense that refers to bivalves that burrow in sediment as opposed to those bivalves that attach themselves to substrate (such as mussels and oysters). The term has also been used to describe ones that can swim and/or are migratory creatures (such as scallops). In the United Kingdom, the word “clam” is one of the common names of various species of marine bivalve mollusks. However it is not generally used to cover edible clams that burrow.
Clams are equipped with “clam shells”. These shells resemble a hinged container that consists of two equal halves that lock together. When clams feel threatened they “clam up” and withdraw back into their shell. These creatures also have open circulatory systems which mean that their organs are surrounded by watery blood that contains oxygen and nutrients. There are over 15,000 different species of clams worldwide and they come in a variety of different sizes and colors. (Shades of brown, red-brown, yellow, cream, etc.)
These creatures burrow under the sea floor and their shells protect their soft bodies. Most clams are typically only a few inches long. The clam’s head is located within its shell and is rudimentary, without eyes or antennae. Water containing oxygen and food particles can be found entering through the clam’s incurrent siphon (two tubes that project from the end opposite of the foot and may be united in a single structure referred to as the “neck”). Waste containing water is expelled through an excurrent siphon.
Clams usually have separate sexes and when they reproduce their eggs and sperm are deposited into the water, where the fertilized egg then develops into a free swimming larva without a shell that may not reach its adult form until several months later.
As one can easily see, turtles and clams are not related and are very different from one another in a number of various ways.
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