How to count syllables for affricates

I was reading about readability tests and it says

The sentence "The Australian platypus is seemingly a hybrid of a mammal and reptilian creature." scores 37.5 as it has 24 syllables and 13 words.

Word count:

 1    2          3       4     5     6   7     8 9   10    11    12
The Australian platypus is seemingly a hybrid of a mammal and reptilian 

  13
creature.

Syllables count:

 1   2   3   4    5  6   7   8  9   10  11 12 13  14  15 16 17  18  19  20  21 
The Aus tra lian pla ty pus is see ming ly  a hy brid of a  ma mmal and rep ti

22 23  24  25 26
li an crea tu re.

I think that 22 and 23 are making diphtongue so they should be counted as one and 25 is an affricate vowel

so.. why do I count 25 instead of 24?

To make 24 you would count the syllables like this:

1   2   3    4   5   6  7   8  9   10   11 12 13 14   15 16 17 18
The Aus tral ian pla ty pus is see ming ly a  hy brid of a  ma mmal

19  20  21  22  23   24
 nd rep til ian crea ture.

I think it's arguable whether the -ian is one or two syllables though.

Probably depends on dialect/accent as Colin mentions in comments.

Some would pronounce it yun - Aust-rail-yun - which is how the counting above must be doing. Others would pronounce it ee-un - Aust-ray-lee-un - I would pronounce it like this as a native BrE speaker.

Perhaps this is a BrE/AmE thing? (Thinking of Indian usage in western cowboy films = Ind-ee-un/Ind-yun)