I like the design a lot, it's like an adorably chubby, shell-less turtle. The one suggestion I'd make is combine the first few sentences, since it seems rather awkward that they appear to be 1 to 2 sentence long paragraphs. Alternatively, perhaps make them longer.
"As they are nocturnal and Seashrogs diurnal"
Should this be "As they are nocturnal and Seashrogs are diurnal"?
As for whether or not Twinkiiros and/or Twinkorals are able to survive on the driftwood islands, they should be fine, especially the former, since all that decay should in fact help facilitate their growth, especially since it would be save to assume several species would adapt to living along their submerged shorelines.
- - -
Also, a heads up, but the Prime Specimen contest has been extended to June 12th. That means everyone has more time to work on their submission(s).