Maylandia (Teleostei: Cichlidae) Remains a Nomen Nudum

Abstract

The debate of the validity of Maylandia vs. Metriaclima as a genus for a group of rock-dwelling cichlids (Pseudotropheus zebra complex) in Lake Malawi, Africa, has been argued for more than 25 years. Probably the most important requirement in describing new zoological taxa is Article 13.1.1 of the International Code of Zoological Nomenclature (ICZN, 4th edition). We demonstrate that the description of Maylandia did not meet these requirements. Thus, we maintain that Maylandia remains a nomen nudum.

1. Introduction

The debate regarding the validity of either Maylandia, suggested by Meyer & Foerster 1984 [1] or Metriaclima, suggested by Stauffer et al. 1997 [2] has recently been reactivated by Scharpf [3], who stated that Maylandia is valid and thus Metriaclima is a junior synonym. Because of our work involving these cichlids from Lake Malawi that described multiple species using the genus name Metriaclima, there is a need to explain in detail why we interpret Maylandia as a nomen nudum. A nomen nudum is a Latin term referring to a name that fails to conform to Article 13 of the ICZN. A nomen nudum is not an available name; therefore the same name may be made available later for the same or a different concept [4].

In 1970, when the first cichlids from Lake Malawi were exported for the ornamental fish trade, the smaller, rock-dwelling cichlids of Lake Malawi, locally known as mbuna, were classified in nine genera, with only two containing more than two species, i.e., Melanochromis, identified by Trewavas 1935 [5], with 5 species and Pseudotropheus, identified by Regan 1921 [6] with 7 species. Many new species were described in the years following, the majority of them in aquarium magazines, due to the exportation of live fishes for the aquarium trade; by 1983, the mbuna were classified in 10 genera, with Melanochromis containing 11 species and 29 in Pseudotropheus. Many more species were discovered by Ribbink et al. [7], who listed 125 species in Pseudotropheus, most with cheironyms. They also recognized several species complexes within the genus, with the Pseudotropheus zebra species complex containing 27 species and the Pseudotropheus tropheops species complex containing 34 species. Meyer and Foerster [1] described Pseudotropheus greshakei and proposed a new subgenus, Maylandia, with the new species as type species. However, since no differentiating characters between Ps. greshakei and Ps. williamsi (Günther 1894), the type species of Pseudotropheus, were given, the name Maylandia was considered a nomen nudum by Stauffer et al. [2], who introduced the genus Metriaclima to contain essentially the same group of species. Although the name Maylandia had not been used since 1984, a fierce discussion ensued about the justification of the nomen nudum declaration. The entire debate has been comprehensively summarized in a recent paper by Scharpf [3], who declared that Maylandia is a validly described subgenus and that Metriaclima should be rejected as a junior synonym. However, the same arguments in favour of Maylandia were presented and no new insights were offered convincing others of his interpretation. Moreover, Scharpf [3] (p. 467) advises editors and peer reviewers to reject Metriaclima and use Maylandia instead. Taxonomy is a matter of consensus, and everybody is entitled to hold and express their own opinion. Herein, we explain in detail why we interpret Maylandia, as posed by Meyer and Foerster, as a nomen nudum, not to convince the debate’s opposition, but to give a background explaining why we will continue to use Metriaclima, as we have for the last 25 years.

2. Materials and Methods

Probably the most important requirement in describing new zoological taxa is Article 13.1.1 of the International Code of Zoological Nomenclature (ICZN) [8], introduced in the second edition in 1964 (as Article 13a), which states that a new taxon must be “accompanied by a statement that purports to give characters differentiating the taxon.” It does not require that such characters are useful, and the four characters that proponents of Maylandia claim constitute the diagnosis of the subgenus would not be considered as such. Below we give the first few paragraphs of Meyer and Foerster [1] under the heading “Maylandia n. subgen.” and provide information that demonstrates that Article 13 was not followed.

3. Results

The description of the proposed subgenus starts as follows: “The subgenus differs in several points from the type species of Pseudotropheus, Ps. williamsi, the supplementary description of which precedes this work in this same fascicle (Trewavas: 97). In this species, the jaw teeth are arranged regularly in curved bands, the internal teeth are tricuspid, the pharyngeal teeth are loosely packed and relatively large, and the melanin pattern of the body consists of longitudinal rows of spots or broken lines, instead of vertical bars.”

After this sentence one would expect a statement that mentions in what manner the new subgenus (or Ps. greshakei, its type species) differs from the characters of Ps. williamsi, but that is not the case, as it is followed by:

“Some other species of Pseudotropheus, s. lat., resemble Ps. greshakei and differ from Ps. williamsi in the internal rows of teeth being less regular and, at least in adults, including many unicuspids, the pharyngeal teeth being fine and very closely packed posteriorly, and the melanin pattern of the body forming more or less conspicuous vertical bars. These are Ps. zebra Boulenger, Ps. aurora Burgess, Ps. lombardoi Burgess, and Ps. livingstonii Boulenger.”

Scharpf [3]—and others before him—argue that these are the diagnostic characters defining the subgenus Maylandia and he lists them in a table on page 463, but that is not what the text says, as these characters are attributed to only those four species. Moreover, the authors Meyer and Foerster [1] do not regard these characters as defining the subgenus because a little later they state “We suggest that this “zebra complex” be included in the subgenus Maylandia.” Why would there be any doubt about including these four species in Maylandia if they comply with the alleged diagnosis?

Furthermore, the authors suggested including this “zebra complex” in the subgenus Maylandia, but not that this complex should be regarded as equating to the subgenus Maylandia. This indicates that this complex forms only part of the proposed subgenus and, furthermore, that the authors did not regard their subgenus as being monotypic, which could have validated their description by adopting the differentiating characters of the type species.

In the same publication [1], the description of Ps. greshakei precedes that of Maylandia, but that species is not differentiated from Ps. williamsi. The text below the heading “Diagnosis” only contains morphological measurements and meristic values of the new species, but no characters differentiating it from related or similar species. However, such characters appear under the heading “Affinités”, where the new taxon is distinguished from Ps. aurora, Ps. lombardoi, Ps. livingstonii, and Ps. zebra. These differentiating characters refer to the diameter of the eye, length of snout, interorbital width, number of gillrakers, structure of teeth, number of dorsal-fin spines, and male coloration. Together, these characters form the diagnosis of Ps. greshakei, but since it was not differentiated from Ps. williamsi, the type species of Pseudotropheus, it is unclear whether (some of) these characters define Maylandia or (some of) them distinguish Ps. aurora, Ps. lombardoi, Ps. livingstonii, and Ps. zebra from Ps. williamsi. It is thus an error to assume that the characters “the internal rows of teeth less regular and, at least in adults, comprising many unicuspids, the pharyngeal teeth thin and very crowded posteriorly, and the melanin pattern of the body forming more or less conspicuous vertical bars,” [1] (p. 112) define the subgenus Maylandia, because that is not what is written and it is not supported by the authors themselves. Due to the fact that the new taxon is not “accompanied by a description or definition that states in words characters that are purported to differentiate the taxon” [8], the name Maylandia remains a nomen nudum.

4. Discussion

Since it appears “quite beyond comprehension” [9] for some why the opponents of Maylandia are adamant in explaining over and over again why descriptions authored by Meyer need “an uncompr[o]misingly strict or literal reading” [3], we would like to point out that the lack of a proper diagnosis was not a glitch in the description by Meyer & Foerster but more of a symptomatic error. It was not the only time Manfred Meyer produced a nomen nudum, as Meyer, Foerster, and Dieckhoff [10] attempted to describe Lamprologus kiritvaithai honoring Mr. Kirit Vaitha of Kigoma, Tanzania. Apart from the fact that the species had already been described by Steindachner in 1909, the description by Meyer et al. [10] does not contain differentiating characters for their new species and as such does not comply with the requirements of the Code (article 13). In 1987, Meyer, Riehl, and Zetzsche [11] attempted to describe six new species in Aulonocara, i.e., A. ethelwynnae, A. hansbaenschi, A. hueseri, A. korneliae, A. saulosi, and A. steveni; however, none of the text describing the six species contained distinguishing characters, just lists of morphological characters pertaining to the species at hand, even under the heading “Combined Diagnosis.” In principle these six names represent nomina nuda, but since aquarists (basically the only people using these names) know what species is intended for each of the names given, not much confusion has arisen since. Interestingly, every one of Meyer’s publications regarding cichlids has a section headed “diagnosis”, but the paragraphs below such headings only list morphological measurements and meristics, but no diagnosis in the sense of the Zoological Code, in which characters are given that explain how the new taxon purportedly differs from related or similar taxa. However, the saving grace in several of his publications is the often-appearing section headed “Relationships” or “Affinités”, in which the new taxon is differentiated, such as in the Meyer & Foerster [1] publication describing Ps. greshakei.

Condé & Gery [12] probably understood the problem with the name Maylandia and, in an effort to validate the name, claimed that Meyer and Foerster [1] suggested it as a monotypic subgenus, which would have satisfied the criteria of the Code. However, it is clear from the text that Meyer and Foerster did not regard Maylandia as monotypic.

Beyond our comprehension is why some authors “obstinately assert” [9] that Maylandia is a properly described subgenus and that the work of Meyer, who is a specialist in livebearers and had no prior knowledge of cichlids when describing them in the 1980s, needs to be accepted at any cost, while the author himself never publicly defended the challenges to his publications. Lacking any defense of the name Maylandia by the original authors, we are left to interpret the text that was published. In contrast to Scharpf [3], who proclaims that “authors of future taxonomic publications on cichlids from Lake Malawi, and their editors and peer reviewers, should reject Metriaclima and use Maylandia instead,” we will not forbid anybody from using the name Maylandia. The usage of both names is mainly caused by the fact that the nomen Maylandia is listed as valid on the website “Eschmeyer’s Catalog of Fishes” [13], which is a very useful website referred to by many others, but it appears to represent a personal opinion because it does not respect Stauffer et al.’s conclusion to declare Maylandia a nomen nudum in 1997 [2].