The recent Pluto flyby inspired me to go on an etymological journey and take a look into the world of invertebrates with the same name. This time, to find Pluto I didn’t go to space. Instead I investigated books and files about creatures found in the depths of the ocean, in reefs, or lurking in underwater caves. In my inquiry, I found that invertebrates named after Pluto, god of the underworld in ancient Greek mythology, truly live up to their name.
This project took me into the Invertebrate Zoology library, which is filled with shelf after shelf of books, with lists of species, guides, and hand-drawn illustrations of specimens. The first subject of my research was the swimming crab Atoportunus pluto, and to decode its name, I had to look back thousands of years to ancient Greek mythology. First, I pulled apart the name to understand the genus: “atopos” means “strange” in ancient Greek, and Portunus was son of the Greek god Hephaestus, and was the god of ports. This specific species is named after Pluto, god of the netherworld, and alludes to its habit of residing in caves, which has led to a nearly pigment-less exoskeleton. These crabs truly look like creatures of the underworld!
Another invertebrate’s name, Crassispira pluto, is derived from Latin. Crassispira pluto is a gastropod mollusk with an elongated fusiform and a unicuspid central tooth (essentially one tooth that comes to a point), and dates back as far as the upper Cretaceous. The prefix “crass(i)-” means thick and describes the comparative width of the “spira,” or spiral; the species name pluto denotes this mollusk’s dark coloration. Originally named by Pilsbury and Lowe in 1932, this species is located in the waters of western Mexico.
Through studying these species, I discovered that the huge variety of organisms with the species name “pluto” didn’t receive this name based on a single trait, but a large range of traits. For example, in the case of Hyperbionyx pluto, pluto refers to the depth at which the crustacean lives in the hyperbenthic layer of the north-east Atlantic. For this species, the genus name “Hyper-” means extreme, and “-bionyx” refers to its dark pigmentation.
This trait of dark pigmentation is also shared with the cephalopod Opisthoteuthis pluto; here, the dark pigment is connected to the darkness of the underworld, which is, of course, Pluto’s domain. Opisthoteuthis pluto is a deep-sea octopus that lives as deep as 450 fathoms under the ocean’s surface. The genus Opisthoteuthis is receiving a lot of attention from researchers because one its species appears to be the cutest octopus ever. While that belief may be up for debate, this next fact isn’t. O. pluto, the gothic cousin of O. "adorabilis", uses camouflage to hide its body within the dark sedimentary seafloor off the Great Australian Bight. Furthermore, these octopi may look cute and cuddly but they have a tough bite! They eat shellfish, lobsters, and crabs by easily crushing their shells in their beaks. In 1918, the researcher S. S. Berry discovered another octopus, which he called O. persephone, that was lighter in color than O. pluto. In Greek mythology, Persephone is Pluto’s wife, and her yearly journey out of the underworld brings about spring and life on Earth, hence the lighter pigment in O. persephone alludes to Persephone’s purity and virtue.
In many cases, the names of these creatures are under dispute due to changes in their classification following more accurate identification based on additional data and new definitions for genera. In 1919, Ralph Chamberlin described a genus of polychaetes “includ[ing] abyssal, fragile benthic species,” naming them Ilyphagus. “Ilys-,” which means mud in Latin alludes to their preference to burrow in deep-sea sediments. The other half of the genus name, “-phagus,” means “glutton” and refers to the wide disc-like shape of its body. In this case, the name pluto refers to the fact that this species inhabits sediments of the deep ocean. The problem with Chamberlin’s initial identification of Ilyphagus pluto as a polychaete was that this worm lacks a cephalic cage (bristles encircling the mouth), which is a primary trait of polychaetes. In 1977, the National Museum of Natural History’s very own Kristian Fauchald, a polychaete specialist, wrote the modern definition for polychaetes that stated a cephalic cage was a required trait for classification as a polychaete. Ilyphagus pluto is now considered a holothurian, otherwise known as a sea cucumber.
Finally, the name “pluto” must also carry bad luck: of the eight species initially named pluto, only five names are still accepted. The journey for the name pluto has ended for me but the search for creatures deep in the oceans is never-ending, and soon enough more organisms reminiscent of the netherworld will pop up and be named after the eerie Greek god once again.
By—Zoe Grabenstetter, Intern [Editors: Allen Collins, Elizabeth Boatman]
Reference:
More about Opisthoteuthis pluto from IZ's Antarctic Invertebrates website.
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