Risoid or Rissoid: How To spell?
The word Risoid is misspelled against Rissoid, a noun meaning "Any one of very numerous species of small spiral gastropods of the genus Rissoa, or family Rissoidae, found both in fresh and salt water."
Rissoid has double "ss" is mispronounced as "s"Remember double 'SS' in between the strings ri & oid which should not be misspelled with single 'S'
Wrong Spelling:  ri-s-oid  Correct Spelling:  ri-ss-oid 
Find more incorrect spellings of Rissoid to spell right way.