Maylandia, Metriaclima, or Pseudotropheus?

Pseudotropheus (or Maylandia) zebra, BB male, photo from Ribbink et al. (1983)

any aquarists and biologists have recently begun to see new and unfamiliar generic names applied to the Mbuna long familiar as Pseudotropheus zebra, shown in the above photo from Ribbink et al. (1983). Two different names are in competition for use with this Mbuna species, and the other species believed to be closely related to it (see checklist). This page is an attempt to explain the issues surrounding use of the generic names Maylandia, Metriaclima, and Pseudotropheus. I will show that, if a separate genus is to be recognized for the Pseudotropheus zebra group, the correct generic name is Maylandia. Condé and Géry (1999) concluded that Maylandia must be accepted as having priority over its junior synonym, Metriaclima. Géry is a respected senior French ichthyologist. The authoritative Catalog of Fishes by Eschmeyer, Fricke, and van der Laan (see entries here and here), agrees that Maylandia is the valid name (notwithstanding the contrary view of Konings, 1999a and elsewhere). Eschmeyer, who literally wrote the book on the generic names of all living fishes and is expert at applying the rules of the International Code of Zoological Nomenclature, examined the original publication describing and naming Maylandia and concluded that it is "Incorrectly regarded as an invalid name by Stauffer et al." and that "sufficient distinguishing features were provided in the original description" (contra the view of Stauffer and of Konings).
Priority is a basic principle of zoological taxonomy. In general, the oldest name validly published for an animal (according to a specific set of rules) is accepted.
Of the three generic names, Pseudotropheus is the oldest, having been proposed by Regan (1922). Its "type species" is P. williamsi. Quite a few Pseudotropheus species have been described since 1922, the number rapidly climbing in the 1980s and '90s.
The increasing number of (increasingly diverse) species reached a crisis by 1984, when two sets of authors decided that there were too many Pseudotropheus species, and they were too dissimilar to the type species P. williamsi, for convenience and for accurate reflection of reality. In that year Trewavas (1984a), an expert English taxonomist specializing in African cichlids, proposed the Pseudotropheus subgenus Tropheops (notice that it is capitalized). This subgenus could (optionally) be used for members of the P. tropheops group. Thus, for example, if the subgeneric names were to be used in a particular publication, P. williamsi could be called Pseudotropheus (Pseudotropheus) williamsi, while P. tropheops could be called Pseudotropheus (Tropheops) tropheops. Species presumed to be related could be grouped in the same subgenus and so distinguished, as a community of relatives, from members of the other subgenus: P. (P.) williamsi versus P. (T.) tropheops, P. (T.) macrophthalmus, P. (T.) microstoma, and so on.
Also in 1984, Meyer & Foerster proposed a new subgenus for a different section of Pseudotropheus — the subgenus Maylandia, whose type species was their new species P. greshakei, a species very close to P. zebra. Now there were three subgenera in Pseudotropheus, and P. (M.) greshakei and other zebra relatives had their own subgenus, again optionally usable to show presumed relationship. (Optional, because you needn't use a subgeneric name just because it's available; it tells "more than you need to know" in many situations.)
ow, it is important to realize that under the rules of zoological nomenclature, both a genus and a subgenus are "genus-group names," and that a name published at either level is also available at the other level. Thus, Pseudotropheus itself is also available as a subgenus, the "nominate" subgenus of Pseudotropheus. So, as soon as Pseudotropheus (Maylandia) was published as a subgenus, Maylandia also became available as a genus, if anyone cared to use it for P. (M.) greshakei and the other "zebras." Regan's publication of the genus Pseudotropheus in 1922 automatically made available a subgenus Pseudotropheus, which would only be used if and when a different subgenus, with a type species other than P. williamsi, was ever named — which happened in 1984.
Fast-forward to Halloween (31 October) 1997. Dr. Jay Stauffer of Penn State and several colleagues published a revision of the zebra complex (Stauffer, Bowers, Kellogg, & McKaye, 1997). These authors coined the name Metriaclima as a genus for the zebras (p. 191). They were aware of the prior Maylandia publication, and briefly mentioned the name Maylandia, but dismissed it in just a few words (p. 193):
"Meyer and Foerster (1984) suggested that certain members of this [zebra] group be included in the [Pseudotropheus] subgenus Maylandia; however, although Maylandia was proposed as a subgenus no description or diagnosis accompanied this suggestion. Therefore, Maylandia, in effect, is a nomen nudum and thus an invalid name."
In fact, however, Meyer & Foerster did provide a diagnosis and a description of Maylandia and its type species, M. greshakei. I have studied the original description of Maylandia and reviewed the requirements for valid publication and availability in the International Code of Zoological Nomenclature. I have to conclude that the publication of Maylandia — despite minor shortcomings — must be accepted as valid and available as a genus for the zebra group. (By popular demand, further discussion of the technicalities is now available here.) Therefore, Maylandia has priority over the later name Metriaclima for the same group, and so Maylandia has to be used as the genus for the group if it is recognized as a genus separate from Pseudotropheus. Is there unanimity on which name to use? No, not yet, but the priority of Maylandia over Metriaclima is acknowledged by several other cichlid scientists and this name will surely prevail.
ut wait; there's more! Remember the Pseudotropheus subgenus Tropheops. If the zebra group is to be recognized as a full genus, under whichever name (and the decision of genus versus subgenus is also open to judgment), then for logical consistency, species tropheops and its presumed relatives should also be split off into a full genus Tropheops. (Fish genera often start out as subgenera and then get "promoted" later, when some "splitter" taxonomist believes that unrelated species are being kept together, or wants fewer species per genus and wishes to emphasize differences between species rather than similarities.) This leaves P. williamsi, and any relatives that may be identified, in Pseudotropheus proper — along with many species most experts do not think are closely related to Pseudotropheus williamsi, such as P. elongatus and its relatives, and the Pseudotropheus "aggressives," and others. The end of this story has not yet been written!
I hope this explanation clarifies my opinions about these rather involved issues.

The Cichlid Fishes of Lake Malawi, Africa: MalawiCichlids.com