Ptychochromoides Kiener & Mauge

[[Ptychochromoides Kiener & Maugé]]

The endemic Malagasy cichlid genus Ptychochromoides was described by Kiener and Maugé (1966) and was distinguished from members of the closely related genus Ptychochromis Steindachner, 1880, based on subtle differences in pharyngeal dentition. Kiener and Maugé (1966) designated Ptychochromis betsileanus (Boulenger 1899) as the type species of the new genus. Reinthal and Stiassny (1997: 356) discussed additional characters that distinguish Ptychochromoides from Ptychochromis, yet were unable to locate any derived features to unite all members of Ptychochromoides, concluding that monophyly of the genus remained to be established. Sparks and Reinthal (2001) were likewise unable to locate any apomorphic features to unite all members of the genus and concurred with the assessment regarding Ptychochromoides monophyly advanced by Reinthal and Stiassny (1997). Sparks and Reinthal (2001) suggested that a single row of dentition on the second pharyngobranchial toothplate serves to unite all members of the genus, but cautioned that this feature is not restricted to Ptychochromoides within Cichlidae. Results of recent studies of Malagasy cichlids based on nucleotide characters corroborate the findings of both Reinthal and Stiassny (1997) and Sparks and Reinthal (2001), and indicate that Ptychochromoides is not monophyletic with the inclusion of P. katria Reinthal and Stiassny, 1997, which is instead consistently recovered as the sister taxon to Ptychochromis (Sparks 2003, 2004). Unique among the Malagasy-South Asian cichlids, both Ptychochromis and Ptychochromoides katria share a hypertrophied laterosensory canal system on the preopercle, mandible, and the neurocranium, with enlarged canals and markedly expanded pores (Reinthal & Stiassny 1997: fig. 8; Sparks 2001, 2004).

Historically, members of Ptychochromoides were distributed in the central, eastern, and south-central highlands of Madagascar (Kiener 1959, 1963: pl. 92; Sparks & Reinthal 2001; Fig. 1). They are absent from northeastern and northwestern drainages. Populations of Ptychochromoides from the central highlands of Madagascar, Lac Itasy and environs, are presumably extinct. Despite repeated attempts, specimens have not been collected from this region in several decades (Reinthal & Stiassny 1997; Sparks & Reinthal 2001; de Rham & Nourissat 2002). Members of the genus are confined to relatively undisturbed highland rivers and lakes where the water is well oxygenated and water temperatures remain cool throughout the year. Members of Ptychochromoides appear to be restricted to habitats with rocky and sandy substrates. Most commonly they occur in areas of swift flowing water where there are also areas of relatively still water and deep pools (Kiener 1959; Reinthal & Stiassny 1997; Sparks & Reinthal 2001).