From KF.

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And the second piece of the commission for Sanchay  sanchaysquirrel (on FA, you can find her here  Tigergryph ) It was decided that in order for this race to interact with land dwellers, they needed to undergo a transformation spell.

Normally the females (and males) of the race do not possess mammaries, but due to getting the transformation spell from a certain Empire, the default bipedal transformation is into a female form.

The only real way to tell the genders apart is the presence of a large head-fin and mouth tendrils on the males, who also are slightly more lithe then the females.

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In time I shall expand on what KF said above, some of it not as correct as he thinks.