From Paul Loiselle's review of Pachypanchx: Guichenot (1866) described Poecilia nuchimaculata from a single specimen collected
by J. P. Goudot, a French resident of Madagascar from 1835 until his death in the early
1860's. The specimen lacks precise locality data and as Goudot’s journals were lost when
he disappeared while in the field (Dorr, 1997), subsequent efforts to determine its
provenance have proved fruitless. Published data (Huber, 1998) indicate that with regard
to both morphometric and meristic characters the type falls within the range that defines
the Malagasy representatives of the genus Pachypanchax. He noted that the prefrontal
scales of this specimen are smaller than those of other Pachypanchax species, while the
lateralis system consists of open rather than enclosed pores. The caudal squamation is
rather light, with scales present only on the basal third of the fin (de Soutter, pers. com.), a
feature shared with only one other Malagasy congener. Radiographic examination of the
caudal skeleton confirms Huber’s observation that a shallow notch separates the upper
plate, formed by the fusion of third, fourth and fifth hypural bones and the lower plate,
formed by the fusion of the first and second bones. This condition is more reminiscent of ZOOTAXA
that found in many representatives of the Nothobranchidae (upper and lower plates
separated by a deep groove), than that seen in Aplocheilus (hypural skeleton made up of
three independent elements, the upper- and lowermost comprising the fused fourth and
fifth and first and second hypural bones respectively).
In the absence of additional material of P. nuchimaculatus, there is no way to
determine whether the observed anomalies in squamation and caudal skeleton of the type
specimen are idiosyncratic or reflect significant population-level differences. Pending the
acquisition of additional material of this species, it seems advisable to follow Parenti
(1981) and provisionally assign Poecilia nuchimaculata to the genus Pachypanchax
