3. Gorgonian/crinoid-cluster quiz
photograph of cluster of coral-reef invertebrates
  Here are possible answers to the coral-gorgonian cluster quiz:
  1. COMPETITION This looks to be a straightforward instance of competition for space between the gorgonian and coral.
  2. INQUILINISM This is a sneaky one. We've already decided that inquilinism is too similar to commensalism to be useful, but in this case inquilinism may actually be the best descriptor. Here, one organism (the crinoid) shelters its body in a protected space beneath the coral without actually interacting with it, and extends its arms out for feeding. COMPETITION for food may also be going on between the crinoid, gorgonian, and coral, although size and type of particles selected may differ somewhat among the 3 organisms.
  3. MUTUALISM The relationship between these edge-inhabiting sponges and their coral hosts is thought to be advantageous to both participants. In return for protecting the coral (with spicules and chemical toxins) the sponge is provided a nice place to live.
  4. NOT CLEAR This is a difficult one. The way the red sponges are perched on the Mycales sponge/coral combination suggests that they could be just holding their own in some sort of standoff competition for space. They could also be considered parasites, or even mutuals...we need to know more about what is going on in order to decide.