Swamphens (genus Porphyrio) are distributed worldwide (except of course Antarctica), five species are currently officially recognized. In my opinion there are actually more species, 11 to be exact, namely if the Purple Swamphen (species complex) is split into the distinct species which it actually consists of.
And then there are the extinct members including five described species and seven not-yet-described ones.
And … then there are the hypothetical ones … two so far, one of which I have already written about here:
The Tahitian Mountain Goose
The other one is way less mysterious and on the other hand much more mysterious, it is a swamphen from Ra’iatea, Society Islands.
The island of Ra’iatea lies 50 km east of Huahine, the home island of McNab’s Swamphen (Porphyrio mcnabiKirchman & Steadman), one of 12 the extinct swamphen forms known on the basis of subfossil bones only.
What do we actually known about the mysterious bird of today’s post?
Not much. There is a little note among a big listing of Polynesian (including Melanesian and Micronesian) birds, which says the following.:
„319.* Porphyrio sp.
Porphyrio sp. (Schmeltz), Cat. Mus. Godef. 1874 V, p. XVI; Garrett, 1. C. note.
Island of Raiatea, Society Is. (Garrett).
This species is known from two young specimens only.“ 
And that’s it.
I could not find out anything else.
But … the Australian Swamphen is known to be a trampy species and has colonized new Zealand only quite recently, maybe only after the colonization of the islands by the first Polynesians. The same species has also colonized parts of Oceania, where the ssp. pelewensis Hartlaub & Finsch has evolved in Palau and the ssp. samoensis Peale (including. ssp. vitiensis Peale) in western Polynesia.
So, the two Ra’iatean birds may in fact not have been collected on Ra’iatea at all but on another island, or they may have been taken there but may have originated from another place, maybe from Samoa, the closest place where swamphens still exist today.
… or the Ra’iatean birds were indeed a distinct subspecies or perhaps rather species that survived into the 19th century.
Here is a little update for this enigmatic bird.:
“Porphyrio porphyrio (L.), Talève poule-sultane.
La seule citation de l’espèce en Polynésie orientale est due à Wiglesworth (1891b) qui mentionne «Porphyrio species» à Raiatea d’apres deux spécimens immatures collectés par Andrew Garrett. Il semble que les spécimens aient disparu. Il est douteux qu’il s’agisse d’une erreur d’étiquetage car Garrett ne visita certainement pas les Samoa, ni d’autres îles de ‘ouest du Pacifique. Ces oiseaux étaient donc, soit des visiteurs de Samoa, soit les représentants d’une population vivant autrefois à Raiatea et éteinte depuis longtemps.” 
“Porphyrio porphyrio (L.), Purple Swamphen.
The only quotation of the species in Eastern Polynesia is due to Wiglesworth (1891b) which mentions «Porphyrio species» in Raiatea according to two immature specimens collected by Andrew Garrett. The specimens appear to have disappeared. It is doubtful that this was a labeling error because Garrett certainly did not visit Samoa or other islands in the western Pacific. These birds were therefore either visitors from Samoa or representatives of a population formerly living in Raiatea and extinct for a long time.“
 Lionel K. Wiglesworth: Aves polynesiae: a catalogue of the birds of the Polynesian subregion (not including the Sandwich Islands). Berlin: R. Friedlaender & Sohn 1891 In: Abhandlungen und Berichte des Königl. Zoologischen und Anthropologisch-Etnographischen Museums zu Dresden Bd. 3: 1-84. 1890/91. herausgegeben von Hofrath Dr. A. B. Meyer, Director des Museums
 D. T. Holyoak; J.-C. Thibault: Contribution à l’étude des oiseaux de Polynésie orientale. Mémoires du Muséum national d’histoire naturelle 127(1): 1-209. 1984