Well I'm going for this as my first challenge, and really looking forward to it. This is (at least the start of) a sketch of the creature (imaginary - see below) in a side view.

This little lizard critter is a dangerous hunter. It crawls around the sea floor slowly watching carefully for passing fish above. Roughly around 2ft long from nose to rear tailfin, it can shoot a deadly poison cloud from the pipe on it's back, completely paralysing the victim/s. Using its large bunny-like rear legs, it can spring into the waters above to catch its prey before any scavengers can reach it, using its rear fin as a method of speed control during jumps.

I will be most likely improving the drawing anyway tomorrow, so please offer your thoughts and crits as they may well be helpful.