Dive Dry with Dr. Bill

#161: A Jelly "Fish" by any Other Name

Scuba Luv's King Neptune stopped recently at Twin Rocks, a dive site near Goat Harbor. As I descended, my eye was immediately drawn to a beautiful purple striped jelly. We used to call this group "jellyfish," but in this politically correct world no one wants to offend fish by suggesting there is an evolutionary link between such advanced vertebrates and these rather simple invertebrates. Although I may slip on occasion, I'll try to remember to be PC in this column (a real challenge for me, of course).

I was able to follow this nearly intact jelly as it pulsed through the water column. Although simple in structure and biology, its movements were as graceful as some of my favorite dive buddies... and, of course, they don't sting me. Most jellies I encounter near shore have already become the victims of "vicious" attacks from ocean sunfish, kelp bass, garibaldi and the like which often tear portions of the bell apart. I guess those fish were in the mood for something spicy to snack on. Although there was a small bite taken out of this one, it was in very good shape and its swimming was as rhythmic as one can expect.

I've already written about this species in a previous column, so I won't delve into their biology. What I want to talk about today is the name changes this group and this species have undergone. I've already referred to the "jelly" vs "jellyfish" controversy. That applies to the entire group of these simple cnidarians. Hmmm, come to think of it... they weren't always cnidarians either! When I studied biology, the name of the phylum the jellies, corals, anemones and others belonged to was the coelenterates! So this poor creature has had two name changes in the evolutionary groups to which it belongs!

To make matters worse, the purple striped jelly was previously known by the scientific name Pelagia noctiluca. Some biologist decided that this was a case of identity theft! The "purple striped jelly" in our region of the world was larger and had a few other "minor" differences. It was renamed Pelagia colorata. At least the biologist involved did not use this opportunity to name it after him-, or her-, self like many more egotistical scientists have. Decades ago I hoped the species of Helicoplacus (an extinct relative of the sea urchins, sea cucumbers and starfish) I discovered while a student of Steven Jay Gould's at Harvard would be named after me... Helicoplacus drbillbushingus!

In the past, scientists have often separated species based on "minor" differences in their structure, color or other physical feature. While working in the lab late at night, they'd measure the ratios between the radius and the metatarsal bones, or the bill length to skull diameter, or some other set of characteristics and decide they had discovered a "new" species. Since many of these researchers were stuck in some dark hole of a museum, they probably had never seen the animal in its native habitat. In fact Edward F. "Doc" Ricketts (my Cannery Row icon) tells a story about bringing in a specimen of a certain species to the world's expert on that species. The other scientist had to ask what it was, since all he'd seen were parts of the animal pickled in formalin or minute structures through his microscope.

Fortunately biologists now have more accurate methods of determining whether an individual represents a different species or not. I'm talking about molecular biology and DNA sequencing. The evolutionary history and relationship of an organism to closely related forms can be determined through the differences in the pattern of the molecules in its DNA. I recently read that there are only 200,000 differences (out of three billion locations) between humans and chimpanzees. Of course scientists still must judge what constitutes a difference sufficient to separate out a new species. It is still a subjective decision, but there is much more precise evidence to base it on.

When I was a biology student at Harvard too many years ago, I was surrounded by scientists and professors of incredible stature. They included James Watson who, with his co-researcher Francis Crick, first uncovered the structure of DNA (the double helix); E. O. Wilson who is a giant in the fields of evolution and island biogeography (and a major mentor for me back then and one of the reasons I came to Catalina); and Steven Jay Gould, the paleontologist whose many books touched the popular imagination and helped explain evolutionary theory. One of the giants, Ernst Mayr, passed away earlier this year at the age of 100 (didn't see Willard Scott mention him on The Today Show). He was the major intellect behind the modern synthetic theory of evolution.

I used to pass Mayr's office door in the Museum of Comparative Zoology in silence and with great respect. Although I never had him as a professor, two pieces of wisdom were indirectly transmitted from him to me. The first was the definition of species as a group of individuals capable of mating with one another to produce viable, reproductive offspring. I'm not referring to sheep or goats and men in the Mediterranean (or here)... they can't produce viable offspring (except in Greek mythology). All those scientists measuring bones and bills in their dark labs needed this insight before rendering any decision. Regardless of any size, shape or color differences they noted, if the critters can still mate and produce young'uns, they are still the same species. That's one of the reasons I focus so strongly on mating behavior (of course just one of the many reasons!).

Those scientists could also learn from the other insight that Mayr passed on. As a young biologist, Mayr traveled to New Guinea to collect species of birds. He reportedly was killed and eaten by cannibals there, however he obviously survived this rumor. He collected 137 species of birds, carefully skinning each one to add to the museum's collection and then ate them for dinner! He befriended the natives and discovered that these "uneducated" savages identified 136 different species, one less than he counted. They didn't do any measuring in a lab... they studied the birds in their native habitat. They understood their ecology, their munching and mating preferences. Some of those early scientists should have spent more time in the field instead of their dungeons. Real species are more than just a set of unique measurements, different colors or other minor characteristics... both Mayr and the natives knew that!

Whoops, I just discovered during my research that scientists changed the sea jelly's name in 2002 from Pelagia colorata to Chrysaora colorata. I just can't keep up with those guys (and gals)! If you're confused, don't worry... so am I!

© 2005 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays. Buy my "Munching and Mating in the Macrocystis" DVD so you can take Dr. Bill home with you... we'll both be glad you did!

The cnidarian (or coelenterate) sea jelly (or jellyfish) formerly known as Prince... er
I mean Pelagia noctiluca and now as Pelagia colorata, oops Chrysaora colorata!

This document maintained by Dr. Bill Bushing.
Material and images © 2005 Star Thrower Educational Multimedia