Taxonomy & naming
Phallotorynus pankalos was described by Paulo H. F. Lucinda, Roberto E. Reis and colleagues in a 2005 revision of the genus published in Copeia (2005, issue 3, pages 609–631). That paper revised Phallotorynus as a whole and erected three new species, of which P. pankalos is one; Eschmeyer's Catalog of Fishes treats Phallotorynus pankalos Lucinda, Rosa & Reis, 2005 as the valid name. The species sits in the subfamily Poeciliinae of the family Poeciliidae, the New World livebearers, within the order Cyprinodontiformes.
The genus name Phallotorynus is built from the Greek phallos (penis), otos (ear) and rhinos (nose), a reference to the distinctive ear- and nose-like ornaments on the male's gonopodium — the modified intromittent fin that is the diagnostic apparatus of the genus. The species epithet pankalos is a Greek adjective meaning "all-" or "very beautiful," chosen by the authors for the attractiveness of the specimens. In the original diagnosis P. pankalos is distinguished from the similar P. jucundus by having eight dorsal-fin rays rather than nine or ten, eleven anal-fin rays in females rather than ten, the absence of a dark ring around the anus in females, and a dark brown band on the lower jaw.
Morphology
Phallotorynus pankalos is a very small fish, recorded to about 1 in in standard length in the original description. The body is compressed, and meristic counts from the type material give eight soft dorsal-fin rays, eleven soft anal-fin rays and thirty-one vertebrae. The most conspicuous marking is a series of six to nine round, dark brown spots running along the lower half of each flank — the source of the common name "bellyspotted toothcarp" — together with a densely pigmented dorsal fin and a dark brown band on the lower jaw.
As in all Phallotorynus, the defining structure is the male gonopodium, an intromittent organ formed from modified anal-fin rays and bearing the small ear- and nose-shaped processes that give the genus its name. The fine details of these gonopodial ornaments are what separate the species of the genus from one another and were central to the 2005 revision. Beyond the spot pattern, fin-ray counts and jaw band noted above, species-level information on coloration, growth and soft-tissue anatomy is sparse: P. pankalos is known essentially from its original description, and no extensive morphological follow-up has been published.
Habitat
The species is endemic to the upper Rio Paraná basin of south-western Brazil. The type material comes from a tributary (affluent) of the Rio Iguatemi, within the Paraná drainage in the region of Mato Grosso do Sul. FishBase classifies the fish as a freshwater, benthopelagic species of tropical waters, consistent with the small streams and tributary channels of this part of the Paraná system.
Detailed habitat data — water chemistry, flow, substrate and the seasonal regime of its home streams — have not been documented for P. pankalos specifically, and should be read off the broader upper-Paraná tributary setting rather than from species-level measurements. As a small poeciliid of warm lowland-to-upland tributaries, it can reasonably be expected in shallow, vegetated or marginal water, but the cache offers no measured temperature or pH figures, so precise envelopes are treated here as data sparse.
Feeding
No direct dietary study exists for Phallotorynus pankalos. FishBase places the species at a trophic level near 3.0, indicating a carnivorous micropredator that feeds on small invertebrates rather than primarily on plant matter. This matches the general ecology of small poeciliids, which take aquatic insect larvae, micro-crustaceans, and other small drifting or benthic invertebrates from the water column and substrate.
In the absence of gut-content work for the species, finer detail — the proportion of insect larvae to micro-crustaceans, any seasonal shift, or the contribution of algae and detritus — is not known and is not assumed here. What can be said with confidence is only the broad picture: a small, invertebrate-leaning carnivore consistent with the genus and with the trophic estimate in the reference databases.
Mating
Phallotorynus pankalos is a viviparous poeciliid, which means fertilisation is internal. The male transfers sperm to the female using the gonopodium, the modified anal fin that defines the family; in this genus the gonopodium carries the elaborate ear- and nose-like ornaments that give Phallotorynus its name and that serve as key species-diagnostic characters. As in other poeciliids, mating does not involve egg-laying or nest-building: the male approaches the female and uses the gonopodium to inseminate her directly.
No species-specific courtship behaviour has been described for P. pankalos. By analogy with the wider family, males are expected to pursue females and attempt insemination, and females of many poeciliids can store viable sperm internally to fertilise successive broods. Whether P. pankalos shows the pronounced female mate choice documented in better-studied livebearers such as the guppy is unknown; the cache provides no behavioural observations, so these details are left as data sparse rather than inferred.
Breeding
Like all members of the family Poeciliidae represented in this section, Phallotorynus pankalos is a livebearer: after internal fertilisation the female carries the developing embryos and gives birth to free-swimming young rather than laying eggs. FishBase records the reproductive mode as viviparous but provides no species-specific figures for gestation length or brood size, and the original revision is a systematic treatment rather than a reproductive study.
Because no measured brood-size, gestation or superfetation data exist for P. pankalos, none are invented here. Superfetation — the carrying of several broods at different developmental stages simultaneously — is known in some poeciliids but has not been demonstrated for this species, and is therefore not claimed. The honest summary is that P. pankalos reproduces by internal fertilisation and live birth in the poeciliid manner, while the quantitative reproductive biology remains undocumented.
In the aquarium
Phallotorynus pankalos is, for practical purposes, not an aquarium fish. It is a small (under 1 in), geographically restricted Brazilian poeciliid that is essentially absent from the ornamental trade, and no species-specific care, water-parameter or breeding guidance has been published for it. The only husbandry information that can be offered is the generic guidance that applies to small warm-water livebearers, and even that should be treated as inference rather than tested practice for this species.
Anyone encountering the species would most likely do so in a scientific or specialist-collection context rather than through the hobby. In keeping with the editorial standard for this atlas, no invented temperature range, tank size or feeding schedule is asserted here: the responsible statement is that detailed aquarium care for P. pankalos is undocumented, and that maintenance would have to be extrapolated from the general requirements of small Neotropical poeciliids.
Conservation
Phallotorynus pankalos is assessed as Least Concern on the IUCN Red List (assessment dated 7 November 2018; species ID 186759). It is not listed under CITES or CMS and is harmless to humans. FishBase further characterises the species as having high resilience, with an estimated minimum population doubling time of under fifteen months.
The Least Concern listing reflects the absence of a documented major threat at the species level rather than detailed population monitoring. Like other small fishes restricted to particular tributaries of the upper Paraná, P. pankalos could in principle be sensitive to localised habitat change, but no specific threat has been recorded against it in the sources available, and its conservation status is currently stable. As ever, the appropriate aquarist position is precautionary: a narrowly distributed endemic deserves habitat respect even when its formal status is one of low concern.