One reason there are so few marine species designated extinct or endangered is the difficulty of declaring with certainty that no example of a species exists anywhere in the vast oceans. Specialists can cite dozens of cases of marine life that have not been seen for decades, or even a century, but saying those species do not exist anywhere is a more difficult matter.
In 1991, two researchers declared a Panamanian fire coral extinct but had to retract the declaration a year later after several examples of the species were located. Some species can become extinct without being noticed. In the mid 1990's researchers discovered the eelgrass limpet, a tiny snail that once flourished along the Atlantic coast of America, had been wiped out in the 1930's when a fungus destroyed its grass-like host plant.