One ocean sunfish plus one Southern ocean sunfish might equal three

There is a wonderful article by Melissa Hogenboom going around in social media right now. An article about the ocean sunfish, its vertical migrations, and its diet (Weird giant sunfish reveals its secrets). The article describes the results reported in a manuscript by a team led by Itsumi Nakamura of the University of Tokyo, Japan. This manuscript has been accepted for publication in the Journal of Animal Ecology, which is different from a research article that has been published, as the manuscript in question could experience slight changes before its publication.

Melissa’s article is straight forward and accompanied by beautiful photographs, and although it is not a taxonomic paper, it surprised me the name of the study subject was not to be found in the text. I am referring to the binomial name, considering that there are two species of sunfishes that inhabit the coasts of Japan. The ocean sunfish is the common name for Mola mola (Linnaeus, 1758), and Mola ramsayi (Giglioli, 1883) is known as the Southern ocean sunfish (more on the Southern ocean sunfish by the Australian Museum). According to the Catalog of Fishes these are the two valid species names in the genus Mola. The Catalog of Fishes is a public source, updated in a regular basis, that accounts for nomenclature acts (naming) that involve fishes. You can go to the previous link and type “Mola” while selecting species. You will retrieve 54 records. At the end of each species description look for current status. You will quickly notice that not all these names correspond to species in the Family Molidae. Of the 35 species among the members of the family Molidae, many are synonyms of Masturus lanceolatus (Liénard 1840), Mola mola (Linnaeus 1758), Mola ramsayi (Giglioli 1883), Ranzania laevis (Pennant 1776). These species names where proposed between 1776 and the late 1800s and the existence of so many synonyms reflects one thing: there was a lot of confusion about the identity of sunfish species.

Fast forward to the year 2015. Do we know everything that lives on earth? The answer is no. To date we know of at least 32,000 species of fishes. Do we know how many species of the genus Mola can be identified worldwide? A review paper from 2010 (Pope et al. 2010) suggests that there might be at least three different species (more in this great post “Luna, alias “ocean sunfish”. El Pez que más mola”) and points at the work of Yoshita et al. from 2009 on sunfishes from the coasts of Japan, where the morphological differences between Mola ramsayi and Mola mola were stated: Mola ramsayi posses large head bumps (something that we might refer to as a “nose”) vs. a smooth slope on M. mola, deeper bodies compared to M. mola, 14-17 ossicles in the clavus vs. 10-13 ossicles in M. mola (which we would not be able to see unless we have x-ray vision or dissect the fish), and a posterior border of the clavus without a wavy edge vs. a clavus with a wavy edge on M. mola.

Unfortunately, the whereabouts of the material used to describe most of the sunfish species is unknown. The holotype is the specimen (the one), the material object, to which an author assigns a name for (nomenclature act). Fortunately, the holotype of Orthragoriscus ramsayi (synonym of Mola ramsayi) is available for study at the Natural History Museum, London (BMNH 1888.11.29.22), so there is a reference for its name. There is also a holotype for Ozodura orsini (synonym of Mola mola) at the Museo di Zoologia, Università di Bologna, Bologna, Italy (MZUB mount on wall). I am interested in knowing what other secrets about these giants will be revealed in the years to come, about their species diversity, evolution, ecology, physiology, and their parasites. Those parasites that birds eat as the magnificent sunfish lies close to the ocean surface (The Blue Planet, BBC). In the meantime I will continue to be awed by the new knowledge gained on the ecology of Mola mola.

References cited:

Giglioli EH (1883) Zoology at the Fisheries Exhibition. II.–Notes on the Vertebrata. Nature (London) v. 28 (no. 718): 313-316.

Liénard E (1840) Description d’une nouvelle espèce du genre mole (Orthagoriscus, Schn.) découverte à l’île Maurice. Revue Zoologique par la Société Cuvierienne (Paris) v. 3: 291-292.

Linnaeus C (1758) Systema Naturae, Ed. X. (Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.) Holmiae. v. 1: i-ii + 1-824.

Pennant T (1776) British zoology. 4th Edition. London. Vol. 3: Class III. Reptiles. Class IV. Fish. Benjamin White, London. v. 3: 1-425, Pls/. 1-73. [Fishes, p. 41-46, 75-409, pls 8-73.]

Pope E. C., Hays GC, Thys TM, Doyle TK, Sims DW, Queiroz N, Hobson VJ, Kubicek L, Houghton JD (2010) The biology and ecology of the ocean sunfish Mola mola: a review of current knowledge and future research perspectives. Reviews in Fish Biology and Fisheries, 19 January 2010, ISSN 0960-3166 (Print) 1573-5184 (Online), DOI 10.1007/s11160-009-9155-9. 

Yoshita Y, Yamanoue Y, Sagara K, Nishibori M, Kuniyoshi H, Umino T, Sakai Y, Hashimoto H, Gushima K (2009) Phylogenetic relationship of two Mola sunfishes (Tetraodontiformes: Molidae) occurring around the coast of Japan, with notes on their geographical distribution and morphological characteristics. Ichthyological Research 56:232–244. doi:10.1007/s10228-008-0089-3

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Mola mola (Linnaeus, 1758) or Mola ramsayi (Giglioli, 1883)? Photo credit: https://ferrebeekeeper.files.wordpress.com/2015/01/tumblr_n0g942radb1qhgo13o2_1280.jpg
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