Draft ICZN petition to clarify mormyrid nomenclature

Mormyrus Linnaeus, 1758, Mormyrops Müller, 1843, and Marcusenius Gill, 1862 (Teleostei, Osteoglossiformes): proposed conservation of prevailing usage by designation of Mormryus caschive Linnaeus, 1758 as type species of Mormyrus Linnaeus, 1758, Mormyrus anguilloides Linnaeus, 1758 as type species of Mormyrops Müller, 1843, Mormyrus cyprinoides Linnaeus, 1758 as type species of Marcusenius Gill, 1862 and a proposed designation of a neotype for Mormyrus caschive Linnaeus, 1758.

John P. Sullivan

Cornell University Museum of Vertebrates, 159 Sapsucker Woods Rd., Ithaca, New York, USA (e-mail: jpsullivan@cornell.edu)

Abstract. The purpose of this application, under Articles 11.6.1, 75.1, 78.1 and 81.1 [?] of the Code, is to conserve the generic name Mormyrus Linnaeus, 1758 in its prevailing usage by designation of Mormyrus caschive Linnaeus, 1758 as type species. This requires reversing the Commission’s Opinion 77 (1917) and Directions 56 & 57 (1956) that recognized Mormyrus cyprinoides Linnaeus, 1758 as the type species of genus Mormyrus Linnaeus, 1758. This determination was based on an error in Jordan (1917) retracted and corrected in Jordan (1919a). This correction was never reflected in a revision of the ICZN’s ruling. As no type specimen exists, we propose designating BMNH 1862.6.17.18 as neotype of Mormyrus caschive Linnaeus, 1758. Furthermore, while prevailing usage now treats Mormyrus cyprinoides Linnaeus, 1758 as the type species of Marcusenius Gill, 1862 and Mormyrus anguilloides Linnaeus, 1758 as the type species of Mormyrops Müller, these designations were made in a key presented in Gill (1862) in which the author reversed the two names counter to his obvious intention. I propose that to avoid future confusion and promote stability, the type designations reflecting current usage be entered on the Official List.

Keywords. Nomenclature; taxonomy; Actinopterygii; Osteoglossiformes; Mormyridae; Mormyrus; Mormyrops; Marcusenius; Mormyrus caschive; Mormyrops anguilloides; Marcusenius cyprinoides; mormyrids; snoutfish; weakly electric fishes; Africa.

1. The purpose of this petition is to correct and clarify longstanding, related nomenclatural issues within the African weakly electric fish family Mormyridae (Teleostei, Osteoglossiformes). Current practice in mormyrid taxonomy universally assumes

• The type species of genus Mormyrus Linnaeus, 1758 is Mormyrus caschive Linnaeus, 1758

• The type species of genus Mormyrops Müller, 1843 is Mormyrus anguilloides Linnaeus, 1758

• The type species of genus Marcusenius Gill, 1862 is Mormyrus cyprinoides Linnaeus, 1758

However, on the ICZN Official List (Opinion 77, Direction 56, Direction 57), Mormyrus cyprinoides Linnaeus, 1758 is given as the type species of Mormyrus, not Mormyrus caschive. Accordingly, the valid generic name of Marcusenius species in the current sense is Mormyrus and therefore the species currently treated as Mormyrus require a new generic epithet. The oldest available synonym is Scrophicephalus Swainson, 1838 (p. 309) with the type species Mormyrus longipinnis Rüppell, 1832. An attempt to impose the ICZN’s existing ruling on mormyrid generic nomenclature—changing all 66 binomial combinations for the valid species of the two genera—would create enormous confusion and instability. Additionally, while usage today is uniform, there is a history of confusion as to the identity of the type species of Mormyrops Müller, 1843 and Marcusenius Gill, 1862. These issues are unresolved in the Catalog of Fishes (Eschmeyer 2015), the standard reference for ichthyological nomenclature, that indicates that Mormyrus anguilloides Linnaeus, 1758 is type species for both Mormyrops Müller 1843 and Marcusenius Gill 1862. This would imply that Marcusenius Gill 1862 is an objective junior synonym of Mormyrops Müller, 1843. Below I lay out the case that (1) ICZN's ruling on the type species for Mormryus Linnaeus followed a mistake by D.S. Jordan in Part I of his Genera of Fishes (1917) that Jordan himself later corrected and (2) confusion regarding the type species of Marcusenius Gill is due to an error, recognized as such by some, but not by others, in a key by Gill (1862) that introduced the generic name Marcusenius and designated a type species for it and for Mormyrops Müller. These issues form a "veritable Gordian knot" of generic names and type species within this family (Myers, 1960, p. 123) which to untie must be treated together. I recommend actions for the ICZN that will clarify the nomenclature of this group.

2. Mormyrus. Hasselquist (1757, p. 398) described Mormyrus caschive in Iter Palaestinum, a pre-Linnaean rejected work (ICZN Opinion 57) that was posthumously assembled and published by Linnaeus, Hasselquist’s mentor, the year before publication of the tenth edition of Systema Naturae. Hasselquist’s detailed description of Mormyrus caschive corresponds perfectly with the species we know today by this name. Particularly noteworthy is the mention of a cylindrical snout acutely sloped downward from the head: “rostrum admodum declive ante verticem capitis acutiusculum, cylindricum” and a fin-ray count of D.80 P.10 V.6 A.19 C.24. These characteristics in combination describe only one of the four recognized Nilotic Mormyrus species (Boulenger, 1907, p.66; Reizer 1964, p. 35). Hasselquist described no other mormyrid species in this work.

3. In Systema Naturae Ed. 10. (1758, p. 327) Linnaeus introduced the genus Mormyrus with two included species, both from from the Nile, cyprinoides and anguilloides. Under anguilloides, in synonymy, Linnaeus lists “Mormyrus Caschive” of his late student, Hasselquist, citing p. 398 of Hasselquist’s Iter. While type specimens survive of M. cyprinoides and and M. anguilloides, no specimen exists for the Mormyrus caschive of Linnaeus (Ferhholm & Wheeler 1983, S. Kullander, pers. comm. 2015). Linnaeus’ fin-ray counts for Mormyrus caschive are identical to those reported in Iter with the exception of the dorsal-fin ray count for which Linnaeus reports 20 rays instead of 80. It may be that Linnaeus’ decision to treat Mormryus caschive as a synonym of Mormyrus anguilloides and the disparity in the dorsal-fin ray counts were related to his not having a specimen of Mormyrus caschive to examine. (Géry (1968) suggested that the dorsal-fin ray count error could be due from a simple typographical ommission of the Roman numeral "C" from the original "XXC.") Valenciennes (1846), who had specimens of Mormryus caschive at his disposal, considered Linnaeus’ dorsal-ray count of this species “une erreur typographique” and expressed puzzlement at how Linnaeus could have synonymized the two species with such different characteristics (Valenciennes in Cuvier and Valenciennes, 1846, p. 237). Whatever his reasons for doing so, Linnaeus’ synonymy of Mormyrus caschive with M. anguilloides in Systema Naturae renders the name unavailable (ICZN 11.6). However, following Article 11.6.1 of the Code, the name is validated back to Linnaeus by Walbaum's inclusion of Mormyrus caschive in his Petri Artedi sueci genera piscium (1792, p. 632). Mormyrus caschive was similarly treated as a valid species in a number of other early ichthyological works, e.g. Bloch and Schneider, 1801, p. 456; Rüppel, 1829, p.4; and Valenciennes in Cuvier and Valenciennes, 1846, p. 227. [Note: I no longer believe this interpretation is correct. Article 11.6.2 of the Code makes clear that Mormyrus caschive is simply an unavailable name. ~ JPS 7/2022]

4. In a footnote to an 1862 paper concerned primarily with species of the Cichlidae genus Hemichromis that we will revisit below with regard to genera Momryrops and Marcusenius, Gill (1862, p. 139) designated Mormyrus caschive Hasselquist, 1757 as the type species of Momryrus and this formulation was followed by others (Jordan 1919a, p. 167; Reizer, 1964, p. 5) in crediting the species to Hasselquist. However, as noted above, names in Hasselquist, 1757 are unavailable and the name is validated back to Linnaeus, 1758 via Walbaum (1792). Thus, the correct citation for this species is "Mormyrus caschive Linnaeus, 1758." Over the past 50 years most authors (e.g. Taverne, 1972, p.163; Roberts & Stewart, 1976, p. 268; Gosse 1984, vol. 1, p. 99; Catalog of Fishes, 2014) have used this latter, correct formulation. However, recognition of Mormyrus caschive Linnaeus, 1758 as the type species of Mormyrus Linnaeus, 1758 contradicts ICZN Opinion 77 (1917) and Direction 56 &  57 (1956) that recognize Mormyrus cyprinoides Linnaeus, 1758 to be the type species of Mormyrus Linnaeus, 1758. As stated in Direction 56, this determination was based on Jordan’s determination in Part I of Genera of Fishes (1917, p. 17). Jordan, however, retracted this designation in Part II of Genera of Fishes (1919a, p. 167) in a section entitled “Additions and Corrections to Part I,” indicating that Mormyrus caschive Hasselquist “as restricted by Gill” is the type of Mormyrus Linnaeus, “not M. cyprinoides L. as stated in part 1, page 15; this species is the type of Marcusenius Gill.” The ICZN never amended its original ruling. A revised ruling and entry on the Official List is needed to achieve accord with prevailing usage.

5. While the availability of Mormyrus caschive Linnaeus, 1758 is rescued by its use in Walbaum 1792 [see note added to #3 above], no type specimen has been found for it in the Swedish Museum of Natural History by either Fernholm & Wheeler (1983) or more recently by Senior Curator of Fishes Sven Kullander (2015, pers comm.). As stability of this taxon—the type species of the nominal genus for family Mormyridae—is highly desirable, we believe designation of a neotype is warranted. A most suitable specimen, apparently female and 520 mm standard length, is housed at the Natural History Museum, London under accession number BMNH 1862.6.17.18. This specimen is cited as an exemplar of this species in two important works (Günther 1866, Boulenger 1907) and remains in excellent condition despite being more than 150 years old (Fig. 1). It is first cited in Günther (1866, p. 215) as one of “two fine specimens” collected in Khartoum by John Petherick, British Consul to the Sudan (the other is BMNH 1862.6.17.75.) It also appears as the fourth of 14 specimens presented in a table of counts and measurements in Boulenger’s Fishes of the Nile (1907, p. 67), and is the one Boulenger chose for a representative illustration of the species (Fishes of the Nile, plate XII.2). Boulenger’s detailed description of this species (1907, p.66), based in part on this specimen we propose as neotype, obviates the need to repeat a description here.

6. Mormyrops and MarcuseniusMüller (1843, p. 324) published the new genus-group name Mormyrops in Beiträge zur Kenntniss der natürlichen Familien der Fische, in which he included the species Mormyrus anguilloides Linnaeus 1758 and Mormyrus labiatus of Geoffroy Saint-Hilaire 1809, without designating a type. It would fall to Gill (1862, p. 139) to designate a type species for Mormyrops Müller. By this time, Valenciennes in Cuvier and Valenciennes, 1846, p. 266, had synonymized Mormyrus labiatus Geoff. with Mormyrus cyprinoides L. Marcusen (1854, p. 6p. 14) had recognized this synonymy and used the combination Mormyrops cyprinoides. Gill's intention was to designate the senior synonym, at that time properly Mormyrops cyprinoides (Linnaeus 1758), as type of Mormyrops Müller and Mormyrops anguilloides (Linnaeus 1758) as type of his new genus Marcusenius. Unfortunately, Gill would inadvertently switch the names anguilloides and cyprinoides in the key presented in the 1862 footnote and this error would go on to establish current usage. Gill's intention and his error are established by the following observations. In his 1862 footnote, Gill (1862, p. 139) introduced the new mormyrid genus and species Marcusenius brachyistius, but did not designate this new species as type species of Marcusenius. First, Gill states that the new Marcusenius brachyistius is a “congener” of “M. anguilloidesM. Tuckeyi and M. zambanenje” (all species of Mormyrops in the current sense) and then produces a key to genera that reads (inconsistent use of parentheses retained):

Lower jaw prominent, M. anguilloides. L . . . Mormyrops.

Upper jaw longer, (M. cyprinoides L.) . . . . Marcusenius.

In this key the new genus Marcusenius is not associated with anguilloides, the aforementioned "congener" of Marcusenius brachyistius, and "lower jaw prominent" and "upper jaw longer" are mismatched with the indicated species (M. cyprinoides has a prominent lower jaw, not M. anguilloides). A subsequent publication in which Gill reiterated his generic concepts (Gill 1863, p. 443) removes any possible doubt as to his intention. Here Gill reproduces the couplet above in a new key in which anguilloides and cyprinoides have changed positions and then explicitly indicates the type species for the two genera as follows:


Marcusenius anguilloides = Mormyrus anguilloides Linn.


Mormyrops cyprinoides = Mormyrus cyprinoides Linn. (nec Geoffroy.)

Clearly Gill had meant to designate anguilloides as type of his new genus Marcusenius and cyprinoides as type of Mormyrops Müller in the 1862 footnote.

7. Gill’s inadvertent association of Mormyrops with anguilloides and Marcusenius with cyprinoides in his 1862 key determined later usage of these genus-group names, particularly after these were accepted at face value and reiterated by Jordan in parts II & III of his Genera of Fishes (1919a,b). Jordan (1919a, p. 216) recognized Mormyrus anguilloides as the type of Mormyrops Müller (although strangely assigned authorship of Mormyrus anguilloides to Geoffroy St. Hilaire instead of Linnaeus and wrongly attributed the type designation to Müller (1843) who made no such designation). In the following volume (1919b, p.314) Jordan recognized Mormyrus cyprinoides Linnaeus as the type species of Marcusenius Gill, 1862. Prior to Jordan 1919, Boulenger had likewise implicitly considered the anguilloides of Linnaeus the type species of Mormyrops Müller, but treated Marcusenius brachyistius Gill as the type species of Marcusenius Gill (e.g. Boulenger 1899, p. 792; 1909, p. 60) without justification. Boulenger classified the cyprinoides of Linnaeus and other species with globlular swellings or barbels on the lower jaw as Gnathonemus Gill 1863 (type species Mormyrus petersii Günther 1862). Many continued to follow Boulenger's usage post-Jordan 1919 (e.g. Daget 1954, p. 94; David & Poll 1937, Pellegrin 1927, Poll 1939, 1969; Schultz 1942, p. 309; see discussion in Géry, 1968). However, Géry (1968, p. 75), Taverne (1968, p. 86; 1971a, p. 102; 1971b, p. 5; 1972, p. 165) and Gosse (1984, p. 80), following Jordan, not Boulenger, cite the unintentional type species assignment in Gill (1862, p. 139) for Marcusenius and solidified subsequent usage (e.g. Boden et al. 1997, p. 1646; Harder 2000, no pagination; Hopkins et al. 2007, p. 281; Jegu & Lévèque 1984, p. 335; Kramer 2013a, Kramer 2013b, Maake et al., 2014, Roberts & Stewart 1976; Teugels et al. 2001, p. 239.)

8. For the purpose of fixation of type species, Gill's intention in his 1862 publication, made clear in his subsequent 1863 publication, may be irrelevent, since according to the Code the first nomenclatural act taken in respect of a name to achieve fixation of a type species constitutes the only valid such act (ICZN Art. 23.6).* Nonetheless, it is remarkable that so few have recognized that Gill's error was in the first (1862, p. 139) publication. Placing the error in the second (1863, p. 444) publication, Jordan (1919b, p.314) noted that Gill had "by some confusion" transferred the name Marcusenius to Mormyrus anguilloides L. and in agreement Géry (1968, p. 74) says of Gill 1863 p. 444  "il ait interverti par mégarde les espèçes-types de Marcusenius et Mormyrops." Only Eschmeyer (2015) in the Catalog of Fishes entry for genus Marcusenius correctly identifies the locus of the error in Gill 1862 (p. 139) and adheres to Gill's intention in recognizing Mormyrus anguilloides Linnaeus 1758 type of Marcusenius Gill. Eschmeyer's entry notes that Taverne (1972, p. 165) treats the genus Marcusenius as valid "but apparently with wrong type." Strangely, however, the Catalog of Fishes also lists Mormyrus anguilloides Linnaeus 1758 as type of Mormyrops Müller without discussion. Thus, despite current uniformity of usage, confusion lingers regarding the type species of Marcusenius Gill. Although there has been no controversy or confusion in practice regarding the type species of Mormyrops Müller, (all workers post-Gill have treated Mormyrus anguilloides Linnaeus as the implicit or explicit type, in accord with the erroneous type assignment in Gill's 1862 key, contra Gill 1863), a careful reading of Gill's two publications detailed above could destabilize its nomenclature in the future.

9. In order to promote stability of these three genus-group names in Mormryridae, the International Commission on Zoological Nomenclature is accordingly asked:

(1) to rule that the specific name Mormyrus caschive was made available by Walbaum (1792) that validates the name back to Linnaeus, 1758.

(2) to use its plenary power to set aside all previous fixations of name-bearing type for caschive Linnaeus, 1758 as published in the binomen Mormyrus caschive and to designate as neotype specimen BMNH 1862.6.17.18, female, in the Natural History Museum, London;

(3) to use its plenary power to set aside to set aside all previous fixations of type species for the nominal genus Mormyrus Linnaeus, 1758 (Opinion 77 & Direction 56, Direction 57) and to designate Mormyrus caschive Linnaeus, 1758 as the type species.

(4) to use its plenary power to set aside all previous fixations of type species for the nominal genus Mormyrops Müller, 1843 and to designate Mormyrus anguilloides Linnaeus, 1758 as the type species.

(5) to use its plenary power to set aside all previous fixations of type species for the nominal genus Marcusenius Gill, 1862 and to designate Mormyrus cyprinoides Linnaeus, 1758 as the type species.

(6) to emend the entry on the Official List of Generic Names in Zoology for the name Mormyrus Linnaeus,  1758 (gender masculine) to indicate type species Mormyrus caschive Linnaeus, 1758 as ruled in (3) above.

(7) to place on the Official List of Generic Names in Zoology the following names:

(a) Mormyrops Müller, 1843 (gender masculine), type species Mormyrus anguilloides Linnaeus, 1758 as ruled in (4) above;

(b) Marcusenius Gill, 1862 (gender masculine), type species Marcusenius cyprinoides Linnaeus, 1758 as ruled in (5) above;

(8) to emend the entry on the Official List of Specific Names in Zoology for the name cyprinoides Linnaeus, 1758 as published in the binomen Mormyrus cyprinoides Linnaeus, 1758 (specific name of the type species of Mormyrus Linnaeus, 1758) as ruled in (3) above.

(9) to place on the Official List of Specific Names in Zoology the following names:

(a) caschive Linnaeus, 1758, as published in the binomen Mormyrus caschive, the specific name of the type species of Mormyrus Linnaeus, 1758;

(b) anguilloides Linnaeus, 1758, as published in the binomen Mormyrus anguilloides, the specific name of the type species of Mormyrops Müller, 1843;

* [How strict is this when intention of author is clearly contrary to an error in the text?  Apparently Eschmeyer thought Gill's intention should be followed, not the error in the text.]


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Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith