We call them "tortoises" in the UK. Is there a different word in Dutch for the animals with shells that live in the sea, the things we in the UK call "turtles", or are they also "schildpadden"?
If I take it back to the word pad.
- De pad = the toad (so a schildpad is a toad with a shield)
Het pad = the path (obvious completely different to "de pad")
The plural of de pad = de padden (short a)
- The plural of het pad = de paden (long a)
In other words, when singular the difference in definition is highlighted by de/het, in plural the difference is highlighted by the d/dd which results in a different pronunciation of the a.
Therefore If you would say de schildpaden you would be talking about paths with shields (which is hard to make any sense of).