The other day, I was helping some folks out with an identification of a starfish they had photographed diving, but I stopped short of giving them the full species. "Why?" they asked. "Isn't this just the the XXX?" (they quoted the most common and easily identified species).
"Well. Its complicated."
Hard to explain these things in a a few lines on Facebook or on Twitter so I thought I would take an example of how complicated the whole taxonomy and identification process is, using a widely photographed example, a starfish called Fromia monilis.
F. monilis occurs widely throughout the Indo-Pacific. It goes by many common names, Necklace star, Tiled star, Candycane star, Peppermint star, etc. Scientists don't use those names because they're so inconsistently used and often because its a contrived name in a field guide, created as a convenience for readers.
This species is often seen in the wild and is a common species in the aquarium trade. You can see it in shallow-reefs from Okinawa to New Caledonia, in the Philippines, Indonesia, etc. and over to the edge of the Indian Ocean.
Bottom line: This species is distributed over a VAST area. Because it does, the range of variation (discussed below) is likely to be greater.
F. monilis is a bright red and white species with a distinctive color pattern. The plates on its body surface (i.e., the many circles and shapes you see on the body) are also pretty diagnostic. Most of these starfish are about 2-3 inches (about 5-6 cm) in diameter. So far so good.
Here is what I would say is the most commonly encountered and "typical" form of this species.
|From Wikipedia. Here|
Some of these specimens have been in museums for, literally hundreds of years and remain essential to our understanding of how these species are defined.
Many of these species get distinguished by fine character differences on these specimens. Some might vary by plate pattern arrangements, or by the number of spines present on the underside, or the particular shape of granules present on the surface. Its often difficult to synch up these characteristics (i.e. the species definitions) with qualities of the animal when it was alive.
BUT, because of dry specimens above, we can usually look at a specimen like this crazy thing below and tell that it is STILL Fromia monilis.
Specimens in museums, accumulate over time and can be very abundant, giving us an idea of the natural VARIATION of a species. Size. Body forms. Aberrant shapes. etc.
For a species that we have virtually no understanding of, any character variation (without seeing its presence in the population) might be used to distinguish a separate species. Without an understanding of this kind of variation (or having population genetics data of course), someone who has never seen a human being before could separate me from Morgan Freeman as a different species.
The one above (w/the red disk) is from Borneo.
Is this the same species? But simply with a different color pattern?? Or a different species?? Some species of starfish are thought to vary by color based on their food, does this one as well?? How important is the color as a feature in identification?
Here is another closely related species, Fromia nodosa which occurs primarily in the Indian Ocean. This species is primarily distinguished based on the larger and more prominent round plates running down the radius of each arm. But it looks familiar, doesn't it??
This individual is from the Maldives (tropical Southern Indian Ocean). It shows the same pattern as F.monilis above and the distinguishing characteristic is kind of variable itself. In other words, it doesn't always hold up. Does that mean it should just be consolidated into F. monilis??
I initially thought this was Fromia monilis but in fact, they might actually be a separate, already established , but this species might actually be a species in a poorly known genus called Paraferdina. Further examination of specimens and research is needed to figure out which one is which... This specimen is from the Red Sea.
This is mainly to demonstrate the limits of how the colors and patterns get complicated quite quickly.
And yes, at some point, someone may work this out.. Lots of diving and subsequent DNA lab time. Plus looking over photos and museum visits! Woo!
But this also explains why scientists, such as myself, are often more reluctant to give you a full species name for a picture when its sent for identification without a specimen. Are these one species? MANY species? Which ones correspond to pre-existing species?
Falling back on the one, most common name can often disguise the truly rich diversity in these wide-ranging, closely related species which are only now, just becoming understood. I argued that this was also the case with the "Bobbit worm" (Eunice aphroditois)
So, yes. Knowing more doesn't necessarily give you all the answers, but it does give you some pretty exciting questions!