Why is Kwan Yin riding a sea turtle? And maybe to save two related questions, why does Samantabhadra ride an elephant and Majursri ride a lion?

I was meditating with Kwan Yin statute and that was the main distraction, I had no idea why Kwan Yin is on a sea turtle.
Okay, I did my own research and here is what I've come up with so far. Interestingly, the artist is making a reference to this Pali suttra:


  "Monks, suppose that this great earth were totally covered with water,
  and a man were to toss a yoke with a single hole there. A wind from
  the east would push it west, a wind from the west would push it east.
  A wind from the north would push it south, a wind from the south would
  push it north. And suppose a blind sea-turtle were there. It would
  come to the surface once every one hundred years. Now what do you
  think: would that blind sea-turtle, coming to the surface once every
  one hundred years, stick his neck into the yoke with a single hole?"
  "It would be a sheer coincidence, lord, that the blind sea-turtle,
  coming to the surface once every one hundred years, would stick his
  neck into the yoke with a single hole."
  
  "It's likewise a sheer coincidence that one obtains the human state.
  It's likewise a sheer coincidence that a Tathagata, worthy &amp; rightly
  self-awakened, arises in the world. It's likewise a sheer coincidence
  that a doctrine &amp; discipline expounded by a Tathagata appears in the
  world. Now, this human state has been obtained. A Tathagata, worthy &amp;
  rightly self-awakened, has arisen in the world. A doctrine &amp;
  discipline expounded by a Tathagata appears in the world.
  
  "Therefore your duty is the contemplation: 'This is stress...This is
  the origination of stress...This is the cessation of stress...This is
  the path of practice leading to the cessation of stress.'"


http://uwf.edu/wmikulas/webpage/leaves/website/canon/samyutta/sn56-48.html

Other Bodhisattvas and Buddhas are often described as riding a particular animal.

Samantabhadra is explicitly described as riding an elephant in his sutra. Samantabhadra's elephant appears to be another awe inspiring flourish. (At least from my reading of the excerpt of Samantabhadra Meditation Sūtra in Wikipedia.

Wikipedia says of Manjusri and his lion: "Mañjuśrī is often depicted as riding on a blue lion, or sitting on the skin of a lion. This represents the use of wisdom to tame the mind, which is compared to riding or subduing a ferocious lion." Wikipedia doesn't explain why the lions, but elsewhere it's suggested that lions were sort a family symbol of the Sakyas, or it's just a reference to the pali sutra about "The lions Roar", ref: http://www.accesstoinsight.org/lib/authors/nanamoli/wheel390.html

http://en.wikipedia.org/wiki/Shakyasimha