Most alphabets in this family name their letters with old nouns: an ox, a house, a door, a camel. Hebrew and Syriac both kept those names, which is why aleph and alaph still mean an ox in a language where the shape has not looked like one for two thousand years. Mandaic did not keep them.
Instead most Mandaic letters are named by their own sound with a preceding a, so the alphabet reads ab, ag, ad, ah and onward. The name tells a learner how to pronounce the letter and nothing else. A handful of names break the pattern: ushenna, aksa, it, in, dushenna and kad, and those irregular names are among the clearest signs that the Mandaic alphabet is not the Aramaic one relabelled but a set of shapes and names of its own laid over an inherited order.
This has a practical consequence for anyone comparing the alphabets. In Hebrew and Syriac the letter names are themselves evidence of descent, because the nouns match. In Mandaic they are not, and the descent has to be read from the order instead. That is why the atlas links a Mandaic letter to its Hebrew and Syriac counterparts on place in the sequence rather than on any similarity of name or shape.
It is also why letter-name etymology, which is a productive line of inquiry for the other alphabets, has little to work with here. The names are descriptive, and they were made to be.