A simple enough question which at first glance may seem ridiculous. Not so.
To simply state the obvious, that they are limbless reptiles, would only be half true. There are several species of legless lizards found worldwide along with a host of other limbless organisms that could be misidentified.
In order to answer this seemingly simple question, one would need to take other distinguishing factors into account before determining whether a particular species belongs to one group or the other.
Some distinguishing factors are quite visible, whilst others require a closer look at the anatomy and physical characteristics.
It is not so much the individual characteristics, but moreso the combination of several factors that can truly define Serpentes.
One of the easiest mistakes to make is confusing them withamphisbaenians.
Amphisbaenians (tropical worm lizards) are also vertebrates belonging to the same order (Squamata). Although close relatives, they are in fact quite different.
Internally, the right lung is reduced as opposed to the left lung being reduced in all true serpents.
The Skeletal structure too, is different. The head consists of one solid bone whereas in serpents the head consists of several individual bones connected via ligaments.
A more visible distinction in amphisbaenians is the arrangement of their scales into regular rings around the body as opposed to overlapping scales.
Apart from three species, all amphisbaenians are limbless.
The lack of visible ear openings is another factor which can lead to misidentifaction. One such species is theSilvery Legless Lizard (Anniella pulchra). Just like amphisbaenians these lizards possess no external ear openings. However, it does have moveable eyelids, which serpents lack.
Perhaps the most visual characteristic that differentiates serpents from lizards and amphisbaenians are theventral scales. In lizards, the ventral scales have various patterns, never a single row from head to tail as with snakes. Amphisbaenians, as mentioned earlier in this passage, have rows of scales arranged around the body.
One true serpent-like characteristic that does not apply to either lizards nor amphisbaenians is the separation of the lower jaw. In both lizards and amphisbaenians, the bottom jaw is one solid rigid bone. The bottom left and right jaw in serpents however is not fused. Instead a ligament connects the lower jaws to one another.
So what is the definition of a snake?
It is a limbless reptile with a reduced left lung, overlapping scales, without movable eyelids nor external ear openings.
It is always important to correctly identify a species prior to picking it up or handling it.
Many accidents have occured as a result of misidentification (personal experience included), and quite honestly......it's not worth the risk.